<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:4d12201d-fca8-410a-95d6-986f7360435e,g:7a15af18-b2bd-42f0-a2fa-d4d4fa88957c-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://vsecorp.com/role/ConsolidatedStatementsofOperationsUnaudited" xlink:type="simple" xlink:href="vsec-20250630.xsd#ConsolidatedStatementsofOperationsUnaudited"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/ConsolidatedStatementsofOperationsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_15d4b06a-1fd7-4bb1-a368-1830a25b28b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_StatementTable_15d4b06a-1fd7-4bb1-a368-1830a25b28b9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a1a3633e-7b34-44a7-9d42-88d4bddba66c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_15d4b06a-1fd7-4bb1-a368-1830a25b28b9" xlink:to="loc_srt_ProductOrServiceAxis_a1a3633e-7b34-44a7-9d42-88d4bddba66c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a1a3633e-7b34-44a7-9d42-88d4bddba66c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_a1a3633e-7b34-44a7-9d42-88d4bddba66c" xlink:to="loc_srt_ProductsAndServicesDomain_a1a3633e-7b34-44a7-9d42-88d4bddba66c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a4dd1957-c5c4-43f9-bd17-7c098f0e4b34" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_a1a3633e-7b34-44a7-9d42-88d4bddba66c" xlink:to="loc_srt_ProductsAndServicesDomain_a4dd1957-c5c4-43f9-bd17-7c098f0e4b34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_94ead333-3fbb-4d11-8476-b75e47729586" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a4dd1957-c5c4-43f9-bd17-7c098f0e4b34" xlink:to="loc_us-gaap_ProductMember_94ead333-3fbb-4d11-8476-b75e47729586" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_cbf323d2-fc5b-4c4f-83c5-e12f5de9bd19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a4dd1957-c5c4-43f9-bd17-7c098f0e4b34" xlink:to="loc_us-gaap_ServiceMember_cbf323d2-fc5b-4c4f-83c5-e12f5de9bd19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenueAbstract_ce08e01c-07b0-43ca-84b6-9a9db12a6e79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_CostOfRevenueAbstract_ce08e01c-07b0-43ca-84b6-9a9db12a6e79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_51f50132-04ee-42b9-9d1f-74febeae13bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostOfRevenueAbstract_ce08e01c-07b0-43ca-84b6-9a9db12a6e79" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_51f50132-04ee-42b9-9d1f-74febeae13bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingCostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_1b4c01b5-95d9-415f-905d-2d342bd3a9ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_1b4c01b5-95d9-415f-905d-2d342bd3a9ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_e22782a0-4c27-41ba-b5e5-b6cfcd6e1d5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_e22782a0-4c27-41ba-b5e5-b6cfcd6e1d5a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnTerminationOfLease_54f92428-4299-4611-81f7-0b78f3314494" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnTerminationOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:to="loc_us-gaap_GainLossOnTerminationOfLease_54f92428-4299-4611-81f7-0b78f3314494" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_6acf867e-32f4-491b-ad04-0e8dfac3a621" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_6acf867e-32f4-491b-ad04-0e8dfac3a621" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_48f974fd-db31-4c51-a790-eb3b6765532b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingCostsAndExpensesAbstract_5fe6b0af-129f-46b1-8dfc-7384d6c623f7" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_48f974fd-db31-4c51-a790-eb3b6765532b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_5118f41c-1a00-4239-8e5a-4c852abf660c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_OperatingIncomeLoss_5118f41c-1a00-4239-8e5a-4c852abf660c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_954dde34-3a7b-472d-a4fb-d9d8da7363e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_InterestExpenseNonoperating_954dde34-3a7b-472d-a4fb-d9d8da7363e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_0bcf5b37-4d7f-4484-b71d-b42bc61bdea8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_0bcf5b37-4d7f-4484-b71d-b42bc61bdea8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_a524e19e-cbc6-46a5-9865-a8507e9d2567" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_a524e19e-cbc6-46a5-9865-a8507e9d2567" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_33e1f234-6a4f-4229-b2a5-3cd4b6e45217" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_33e1f234-6a4f-4229-b2a5-3cd4b6e45217" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_60925fbb-5113-4b0a-935d-309953cc7a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_60925fbb-5113-4b0a-935d-309953cc7a4c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_d42b9a37-3adc-4376-afdd-c34bf31c5c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_NetIncomeLoss_d42b9a37-3adc-4376-afdd-c34bf31c5c6a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_a4700bcb-677a-4784-8042-c4fe30329d9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_EarningsPerShareAbstract_a4700bcb-677a-4784-8042-c4fe30329d9b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_3edc7d25-7f97-4339-a4f1-ea50c06c6f6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_a4700bcb-677a-4784-8042-c4fe30329d9b" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_3edc7d25-7f97-4339-a4f1-ea50c06c6f6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_4ca9a186-6509-4e47-b4d7-6940825c69fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_3edc7d25-7f97-4339-a4f1-ea50c06c6f6b" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_4ca9a186-6509-4e47-b4d7-6940825c69fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_d68b72ad-7436-49b1-8d0d-38639e072c8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_3edc7d25-7f97-4339-a4f1-ea50c06c6f6b" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_d68b72ad-7436-49b1-8d0d-38639e072c8a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_0464a0ac-7e45-4e5b-a178-9cc4a574fd58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_3edc7d25-7f97-4339-a4f1-ea50c06c6f6b" xlink:to="loc_us-gaap_EarningsPerShareBasic_0464a0ac-7e45-4e5b-a178-9cc4a574fd58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedAbstract_f9849f6a-ccf8-4510-af86-90e6ce0d8133" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_a4700bcb-677a-4784-8042-c4fe30329d9b" xlink:to="loc_us-gaap_EarningsPerShareDilutedAbstract_f9849f6a-ccf8-4510-af86-90e6ce0d8133" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_076d52cc-64ca-485f-97ec-13a9831082bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_f9849f6a-ccf8-4510-af86-90e6ce0d8133" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_076d52cc-64ca-485f-97ec-13a9831082bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_a4675b1c-5c61-4871-a85a-96f5d901508b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_f9849f6a-ccf8-4510-af86-90e6ce0d8133" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_a4675b1c-5c61-4871-a85a-96f5d901508b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_272ec9c2-7b7a-4b17-8863-3427ef73b973" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_f9849f6a-ccf8-4510-af86-90e6ce0d8133" xlink:to="loc_us-gaap_EarningsPerShareDiluted_272ec9c2-7b7a-4b17-8863-3427ef73b973" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_db8ee5c7-16ff-45b3-a4ca-3d6e3ff761c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_db8ee5c7-16ff-45b3-a4ca-3d6e3ff761c3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e4d01cd5-6717-4005-9ea0-f5cbe43bbe53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_db8ee5c7-16ff-45b3-a4ca-3d6e3ff761c3" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_e4d01cd5-6717-4005-9ea0-f5cbe43bbe53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_339098d5-30f0-4d86-bda7-a8334e6d4e78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_db8ee5c7-16ff-45b3-a4ca-3d6e3ff761c3" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_339098d5-30f0-4d86-bda7-a8334e6d4e78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_71ba8f6b-3a16-413d-9807-2de126fc703f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_99a34e0a-2fef-4cc7-b9c6-0c3376fd08f5" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_71ba8f6b-3a16-413d-9807-2de126fc703f" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/ConsolidatedStatementsofStockholdersEquityUnaudited" xlink:type="simple" xlink:href="vsec-20250630.xsd#ConsolidatedStatementsofStockholdersEquityUnaudited"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/ConsolidatedStatementsofStockholdersEquityUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_b9ac2e81-273c-48d7-8d5f-75b074451659" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8aaf2364-7f9f-40ab-8314-5716a19ae397" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_b9ac2e81-273c-48d7-8d5f-75b074451659" xlink:to="loc_us-gaap_StatementTable_8aaf2364-7f9f-40ab-8314-5716a19ae397" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_88f3f311-e401-4a67-8405-513cb43e0e40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8aaf2364-7f9f-40ab-8314-5716a19ae397" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_88f3f311-e401-4a67-8405-513cb43e0e40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_88f3f311-e401-4a67-8405-513cb43e0e40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_88f3f311-e401-4a67-8405-513cb43e0e40" xlink:to="loc_us-gaap_EquityComponentDomain_88f3f311-e401-4a67-8405-513cb43e0e40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_88f3f311-e401-4a67-8405-513cb43e0e40" xlink:to="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_6a64f493-3a26-4d23-820b-b780f6f59a4f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:to="loc_us-gaap_CommonStockMember_6a64f493-3a26-4d23-820b-b780f6f59a4f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_10748102-2731-4e68-a7a7-b29478354f7a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_10748102-2731-4e68-a7a7-b29478354f7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_e69a50a4-328f-44e7-b276-ef258bd648bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:to="loc_us-gaap_RetainedEarningsMember_e69a50a4-328f-44e7-b276-ef258bd648bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a2d1a66a-e89d-464e-812b-d6f3cdb7d32e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8cf79f29-ba08-4c8c-8c09-3ec5323aadf7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a2d1a66a-e89d-464e-812b-d6f3cdb7d32e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b9ac2e81-273c-48d7-8d5f-75b074451659" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f3956f79-c036-4e71-a640-b70a56fafcda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f3956f79-c036-4e71-a640-b70a56fafcda" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_d4999270-ac92-4cd6-b719-ed24143b4111" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockholdersEquity_d4999270-ac92-4cd6-b719-ed24143b4111" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_18e40e5e-358a-4ed7-9159-f40278ccd624" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_NetIncomeLoss_18e40e5e-358a-4ed7-9159-f40278ccd624" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f6fa6b68-1039-4ad9-9568-75be99172257" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f6fa6b68-1039-4ad9-9568-75be99172257" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_4136857a-5dfb-45c7-b0e8-9dfe8dd99c22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_4136857a-5dfb-45c7-b0e8-9dfe8dd99c22" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_691f8f47-c84e-4207-9b33-ef78e8ed877b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_691f8f47-c84e-4207-9b33-ef78e8ed877b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_5a1abc6c-27da-4892-ae7b-fb8191c06c7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_5a1abc6c-27da-4892-ae7b-fb8191c06c7c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_b5bbaf67-9776-43d9-9d26-9a67779dece7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_b5bbaf67-9776-43d9-9d26-9a67779dece7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b0fd855e-6c0d-4080-8469-fef444450da1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_b0fd855e-6c0d-4080-8469-fef444450da1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_6ab08547-a7a1-49bc-808c-837d766314fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_6ab08547-a7a1-49bc-808c-837d766314fc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_161b38d3-c5bf-4ebf-9ab4-65e24051dc45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6f4053ac-561f-487f-b9ae-fb99926607ab" xlink:to="loc_us-gaap_DividendsCommonStockCash_161b38d3-c5bf-4ebf-9ab4-65e24051dc45" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_ff11e667-3b0d-40bf-af1a-d15b2b307b0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_d3011875-27e7-4282-97db-a31c32a7e30a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/AcquisitionsNarrativeDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#AcquisitionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/AcquisitionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_58bf213a-eb5b-4a73-a15c-f243d7398468" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_58bf213a-eb5b-4a73-a15c-f243d7398468" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_0d435643-ae80-4277-8d61-f54bac1de5c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_58bf213a-eb5b-4a73-a15c-f243d7398468" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_0d435643-ae80-4277-8d61-f54bac1de5c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0d435643-ae80-4277-8d61-f54bac1de5c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_0d435643-ae80-4277-8d61-f54bac1de5c9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0d435643-ae80-4277-8d61-f54bac1de5c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_11b108fc-bdf0-44af-812a-75731fe67990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_0d435643-ae80-4277-8d61-f54bac1de5c9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_11b108fc-bdf0-44af-812a-75731fe67990" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_TurbineWeldIndustriesLLCMember_ad6d00bf-6586-444a-92ee-594fd2af33c7" xlink:href="vsec-20250630.xsd#vsec_TurbineWeldIndustriesLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_11b108fc-bdf0-44af-812a-75731fe67990" xlink:to="loc_vsec_TurbineWeldIndustriesLLCMember_ad6d00bf-6586-444a-92ee-594fd2af33c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_TurbineControlsInc.TCIMember_e28f8665-706e-4837-949a-3672d85152f7" xlink:href="vsec-20250630.xsd#vsec_TurbineControlsInc.TCIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_11b108fc-bdf0-44af-812a-75731fe67990" xlink:to="loc_vsec_TurbineControlsInc.TCIMember_e28f8665-706e-4837-949a-3672d85152f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_KellstromAerospaceGroupIncMember_699e2176-6d75-44d2-9449-a0db64e5e0f1" xlink:href="vsec-20250630.xsd#vsec_KellstromAerospaceGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_11b108fc-bdf0-44af-812a-75731fe67990" xlink:to="loc_vsec_KellstromAerospaceGroupIncMember_699e2176-6d75-44d2-9449-a0db64e5e0f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e5ecd541-6769-408f-9374-dfda7e0c7790" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_58bf213a-eb5b-4a73-a15c-f243d7398468" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e5ecd541-6769-408f-9374-dfda7e0c7790" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e5ecd541-6769-408f-9374-dfda7e0c7790_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e5ecd541-6769-408f-9374-dfda7e0c7790" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e5ecd541-6769-408f-9374-dfda7e0c7790_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_990dc469-363d-4ca6-963e-e87abc0d2f90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e5ecd541-6769-408f-9374-dfda7e0c7790" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_990dc469-363d-4ca6-963e-e87abc0d2f90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_c300c7ae-bad3-4635-8802-74ef75ba91af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_990dc469-363d-4ca6-963e-e87abc0d2f90" xlink:to="loc_us-gaap_CustomerRelationshipsMember_c300c7ae-bad3-4635-8802-74ef75ba91af" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_dbcfadb5-774a-403d-97ef-59eec7835c4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityInterestIssuedOrIssuableByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_58bf213a-eb5b-4a73-a15c-f243d7398468" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_dbcfadb5-774a-403d-97ef-59eec7835c4b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_dbcfadb5-774a-403d-97ef-59eec7835c4b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_dbcfadb5-774a-403d-97ef-59eec7835c4b" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_dbcfadb5-774a-403d-97ef-59eec7835c4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_9e5f7bd1-1e46-4275-a8e1-e3d10a397401" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityInterestIssuedOrIssuableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableByTypeAxis_dbcfadb5-774a-403d-97ef-59eec7835c4b" xlink:to="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_9e5f7bd1-1e46-4275-a8e1-e3d10a397401" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_39d9dc24-232c-4f90-b832-8ec8c312f8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityInterestIssuedOrIssuableTypeDomain_9e5f7bd1-1e46-4275-a8e1-e3d10a397401" xlink:to="loc_us-gaap_CommonStockMember_39d9dc24-232c-4f90-b832-8ec8c312f8e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_47118eba-3876-427a-9cd3-12d4cc661b61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_47118eba-3876-427a-9cd3-12d4cc661b61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_19645a40-320e-4bb5-9981-f4454f6fb67d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_19645a40-320e-4bb5-9981-f4454f6fb67d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95f7ae72-e0b7-4cd2-af31-fc456e72d3c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95f7ae72-e0b7-4cd2-af31-fc456e72d3c6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_61dad8f2-b29e-418e-9536-5b5db4f0f81e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_Goodwill_61dad8f2-b29e-418e-9536-5b5db4f0f81e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b606506b-498c-4345-939f-10e026b31ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_b606506b-498c-4345-939f-10e026b31ea6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_e3ef29ed-45fa-478a-a3f3-dbc30fa82c23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_e3ef29ed-45fa-478a-a3f3-dbc30fa82c23" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_4bea0474-9a55-4334-b362-572b7d185faf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_4bea0474-9a55-4334-b362-572b7d185faf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments_2fed9e4b-d10e-4573-af90-7e9b5af5e357" xlink:href="vsec-20250630.xsd#vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments_2fed9e4b-d10e-4573-af90-7e9b5af5e357" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_02368d48-8758-45f6-a574-51a4702017f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_02368d48-8758-45f6-a574-51a4702017f3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_e5231139-190c-41a0-bb77-9e15bfd799ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_e5231139-190c-41a0-bb77-9e15bfd799ef" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_5dcc2d87-5015-401c-98fe-a50810ab2490" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_5dcc2d87-5015-401c-98fe-a50810ab2490" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities_c61bbeff-1509-4123-9bb2-bfacbd61f418" xlink:href="vsec-20250630.xsd#vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredTaxLiabilities_c61bbeff-1509-4123-9bb2-bfacbd61f418" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets_0b620359-fc55-463a-bc5b-a80b5901c410" xlink:href="vsec-20250630.xsd#vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets_0b620359-fc55-463a-bc5b-a80b5901c410" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentWorkingCapitalAdjustment_5224ea72-8397-48cc-a2d5-6a4521e4f836" xlink:href="vsec-20250630.xsd#vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentWorkingCapitalAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_6a3546be-9d36-4cda-afff-dc9dc596a645" xlink:to="loc_vsec_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentWorkingCapitalAdjustment_5224ea72-8397-48cc-a2d5-6a4521e4f836" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/AcquisitionsFairValueofAcquiredAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#AcquisitionsFairValueofAcquiredAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/AcquisitionsFairValueofAcquiredAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f8784da3-d766-4a41-88f5-cd176def6474" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f8784da3-d766-4a41-88f5-cd176def6474" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_83cf6c7d-0228-4450-a4ee-b5c258812cc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_f8784da3-d766-4a41-88f5-cd176def6474" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_83cf6c7d-0228-4450-a4ee-b5c258812cc6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83cf6c7d-0228-4450-a4ee-b5c258812cc6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_83cf6c7d-0228-4450-a4ee-b5c258812cc6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_83cf6c7d-0228-4450-a4ee-b5c258812cc6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_163cd112-c8b3-4f65-8fc5-f67e0fdcb364" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_83cf6c7d-0228-4450-a4ee-b5c258812cc6" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_163cd112-c8b3-4f65-8fc5-f67e0fdcb364" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_TurbineControlsInc.TCIMember_c57d47f8-c838-4797-8241-724cbb617a23" xlink:href="vsec-20250630.xsd#vsec_TurbineControlsInc.TCIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_163cd112-c8b3-4f65-8fc5-f67e0fdcb364" xlink:to="loc_vsec_TurbineControlsInc.TCIMember_c57d47f8-c838-4797-8241-724cbb617a23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_KellstromAerospaceGroupIncMember_eb93d0e0-01e3-440f-8ea8-70e82a18eb0d" xlink:href="vsec-20250630.xsd#vsec_KellstromAerospaceGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_163cd112-c8b3-4f65-8fc5-f67e0fdcb364" xlink:to="loc_vsec_KellstromAerospaceGroupIncMember_eb93d0e0-01e3-440f-8ea8-70e82a18eb0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_56248112-69c0-47ca-8d8d-4bf1a6196775" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_56248112-69c0-47ca-8d8d-4bf1a6196775" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractAssets_62d089e9-8e4a-40bf-9d46-117f58721475" xlink:href="vsec-20250630.xsd#vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractAssets_62d089e9-8e4a-40bf-9d46-117f58721475" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_b762dfb9-6a9d-47ac-8dfc-b498f70d0ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_b762dfb9-6a9d-47ac-8dfc-b498f70d0ae6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_f5d89d37-2612-4084-abc6-a540d7a2cd36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_f5d89d37-2612-4084-abc6-a540d7a2cd36" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_06293ab7-3181-48e8-8862-e77ebfb2afd2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_06293ab7-3181-48e8-8862-e77ebfb2afd2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95799645-4806-491c-9780-4d13c3c82578" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95799645-4806-491c-9780-4d13c3c82578" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_01f02cc3-b27b-43de-a122-e81056f719f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_01f02cc3-b27b-43de-a122-e81056f719f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_3dd4c618-81f4-4e06-980d-17dbe87174e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_Goodwill_3dd4c618-81f4-4e06-980d-17dbe87174e1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredOperatingLeaseRightOfUseAssets_373f394b-1d30-4104-baf7-e164dbb88eca" xlink:href="vsec-20250630.xsd#vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_vsec_BusinessCombinationRecognizedIdentifiableAssetsAcquiredOperatingLeaseRightOfUseAssets_373f394b-1d30-4104-baf7-e164dbb88eca" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_773a6ba4-6525-4cba-abdb-77f246460de2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_773a6ba4-6525-4cba-abdb-77f246460de2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_0d1c3f22-aefb-452c-b5a4-277b75375718" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets_0d1c3f22-aefb-452c-b5a4-277b75375718" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_bf04d9b8-5f68-48f5-a7ec-37835fcb7357" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_bf04d9b8-5f68-48f5-a7ec-37835fcb7357" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_eaf696dd-512a-4c87-88ca-52c2fd5f4b02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_eaf696dd-512a-4c87-88ca-52c2fd5f4b02" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation_b9c5cc35-2fc5-4eb9-9f89-4006f0b5ec1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCapitalLeaseObligation_b9c5cc35-2fc5-4eb9-9f89-4006f0b5ec1f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_dbe01f9d-01ca-4266-b237-1c9d3d339f89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_dbe01f9d-01ca-4266-b237-1c9d3d339f89" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_1582868b-6667-4d10-a4fd-fec46bc24c23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_1582868b-6667-4d10-a4fd-fec46bc24c23" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_b64e6578-b74d-4e1a-8f5d-0f7680fd75e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_b64e6578-b74d-4e1a-8f5d-0f7680fd75e9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_1df69824-7bbd-4522-a6d6-fca3e54a3689" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_1df69824-7bbd-4522-a6d6-fca3e54a3689" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments_5e87affe-fd88-48c8-a118-965db17e8eb1" xlink:href="vsec-20250630.xsd#vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_f314481c-5d69-423e-a690-4c22a6bf83a7" xlink:to="loc_vsec_PaymentsToAcquireBusinessesNetOfCashAcquiredAndPostCloseAdjustments_5e87affe-fd88-48c8-a118-965db17e8eb1" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/AcquisitionsProFormaInformationDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#AcquisitionsProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/AcquisitionsProFormaInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_c3ab29df-deaf-49a0-9e6c-7e679459a479" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_50ab61da-bbc6-4653-84ee-013d926b2ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c3ab29df-deaf-49a0-9e6c-7e679459a479" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_50ab61da-bbc6-4653-84ee-013d926b2ba5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_d602bee8-a12a-4128-8dd3-a78e80f7ad78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_50ab61da-bbc6-4653-84ee-013d926b2ba5" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_d602bee8-a12a-4128-8dd3-a78e80f7ad78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d602bee8-a12a-4128-8dd3-a78e80f7ad78_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d602bee8-a12a-4128-8dd3-a78e80f7ad78" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d602bee8-a12a-4128-8dd3-a78e80f7ad78_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b327710a-8d8e-4cb2-83b7-ee04c8ecb105" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_d602bee8-a12a-4128-8dd3-a78e80f7ad78" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b327710a-8d8e-4cb2-83b7-ee04c8ecb105" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_TurbineControlsInc.TCIMember_d80152ba-845c-46c1-9b86-182c70314542" xlink:href="vsec-20250630.xsd#vsec_TurbineControlsInc.TCIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b327710a-8d8e-4cb2-83b7-ee04c8ecb105" xlink:to="loc_vsec_TurbineControlsInc.TCIMember_d80152ba-845c-46c1-9b86-182c70314542" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_KellstromAerospaceGroupIncMember_0bd75051-d439-4aaa-86c6-bffbe9fed6c0" xlink:href="vsec-20250630.xsd#vsec_KellstromAerospaceGroupIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_b327710a-8d8e-4cb2-83b7-ee04c8ecb105" xlink:to="loc_vsec_KellstromAerospaceGroupIncMember_0bd75051-d439-4aaa-86c6-bffbe9fed6c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_4c135389-5554-4889-941a-c4015a0c8cd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c3ab29df-deaf-49a0-9e6c-7e679459a479" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_4c135389-5554-4889-941a-c4015a0c8cd4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTax_93f9004b-e2ad-41e8-950d-1e595ef3eca0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionsProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_c3ab29df-deaf-49a0-9e6c-7e679459a479" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTax_93f9004b-e2ad-41e8-950d-1e595ef3eca0" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DiscontinuedOperationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DiscontinuedOperationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c8d97a12-47bc-435d-b514-820b4dea4816" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c8d97a12-47bc-435d-b514-820b4dea4816" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_c2323272-07f8-4cde-9f4a-657c2293b0b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c8d97a12-47bc-435d-b514-820b4dea4816" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_c2323272-07f8-4cde-9f4a-657c2293b0b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_c2323272-07f8-4cde-9f4a-657c2293b0b7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c2323272-07f8-4cde-9f4a-657c2293b0b7" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_c2323272-07f8-4cde-9f4a-657c2293b0b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_a389612f-f6a8-4197-9849-3643d23ebbfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c2323272-07f8-4cde-9f4a-657c2293b0b7" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_a389612f-f6a8-4197-9849-3643d23ebbfb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_51c3cef7-a0c9-4ec9-8795-436f77f43e62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_a389612f-f6a8-4197-9849-3643d23ebbfb" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_51c3cef7-a0c9-4ec9-8795-436f77f43e62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_7281a630-2c5c-4581-a865-87a75e5ca21b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_a389612f-f6a8-4197-9849-3643d23ebbfb" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_7281a630-2c5c-4581-a865-87a75e5ca21b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_aaaa68b7-b8a2-4f02-8407-10459de7449f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c8d97a12-47bc-435d-b514-820b4dea4816" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_aaaa68b7-b8a2-4f02-8407-10459de7449f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_aaaa68b7-b8a2-4f02-8407-10459de7449f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_aaaa68b7-b8a2-4f02-8407-10459de7449f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_aaaa68b7-b8a2-4f02-8407-10459de7449f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_61346fd0-8f3f-4db1-9909-59126ddac717" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_aaaa68b7-b8a2-4f02-8407-10459de7449f" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_61346fd0-8f3f-4db1-9909-59126ddac717" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FleetSaleMember_3b2e42b6-88ca-4b9a-a8a7-1290a91995e5" xlink:href="vsec-20250630.xsd#vsec_FleetSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_61346fd0-8f3f-4db1-9909-59126ddac717" xlink:to="loc_vsec_FleetSaleMember_3b2e42b6-88ca-4b9a-a8a7-1290a91995e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FederalAndDefenseSegmentMember_c772f4c1-49a8-4080-b74d-a0ada31d318d" xlink:href="vsec-20250630.xsd#vsec_FederalAndDefenseSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_61346fd0-8f3f-4db1-9909-59126ddac717" xlink:to="loc_vsec_FederalAndDefenseSegmentMember_c772f4c1-49a8-4080-b74d-a0ada31d318d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_260c05f5-a12e-4388-9272-4bcd782f1703" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_260c05f5-a12e-4388-9272-4bcd782f1703" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_84aa1843-3316-4cd5-b43e-54b557d67797" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_84aa1843-3316-4cd5-b43e-54b557d67797" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCash_9f4060c9-935b-46cf-b3a0-aa564d09eec8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCash_9f4060c9-935b-46cf-b3a0-aa564d09eec8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationConsiderationFinancingReceivable_2538c8de-433d-4460-9871-da4662c9ee7a" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationConsiderationFinancingReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationConsiderationFinancingReceivable_2538c8de-433d-4460-9871-da4662c9ee7a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_2b191498-8f54-4e02-9cee-05a2d09b1f46" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_2b191498-8f54-4e02-9cee-05a2d09b1f46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_6ae33b4a-c61b-4878-80d2-00f8cf62c3f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_6ae33b4a-c61b-4878-80d2-00f8cf62c3f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationsTransactionFees_744363b3-0ff7-400a-8084-0c505d87d566" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationsTransactionFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationsTransactionFees_744363b3-0ff7-400a-8084-0c505d87d566" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_bc90fe3d-38cd-4386-a00a-258eb64969c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf_bc90fe3d-38cd-4386-a00a-258eb64969c4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_b16b9aa1-d90b-4c5e-a113-5a62ea63cbdc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_b16b9aa1-d90b-4c5e-a113-5a62ea63cbdc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities_416aaa05-7a83-41a2-9e62-82a3456ced63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities_416aaa05-7a83-41a2-9e62-82a3456ced63" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustments_5930be9b-ec19-4223-a1d6-0633052997e9" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationWorkingCapitalAdjustments_5930be9b-ec19-4223-a1d6-0633052997e9" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DiscontinuedOperationsNumberOfAgreements_5cb4d11f-b40a-4442-b91e-103f34a897ef" xlink:href="vsec-20250630.xsd#vsec_DiscontinuedOperationsNumberOfAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_vsec_DiscontinuedOperationsNumberOfAgreements_5cb4d11f-b40a-4442-b91e-103f34a897ef" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_d3af2aad-ef36-40d7-b3b1-b8252f879c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_93071de2-c0d4-4c61-ab41-426377542700" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_d3af2aad-ef36-40d7-b3b1-b8252f879c7e" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DiscontinuedOperationsIncomeStatementDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DiscontinuedOperationsIncomeStatementDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DiscontinuedOperationsIncomeStatementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_98982b46-0cd0-4678-8aef-9d3268a2ba8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_98982b46-0cd0-4678-8aef-9d3268a2ba8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_3e702d74-96c8-424c-a90d-3162365fc71a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_98982b46-0cd0-4678-8aef-9d3268a2ba8d" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_3e702d74-96c8-424c-a90d-3162365fc71a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_3e702d74-96c8-424c-a90d-3162365fc71a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_3e702d74-96c8-424c-a90d-3162365fc71a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_3e702d74-96c8-424c-a90d-3162365fc71a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_d39fa7ce-200c-4e56-a455-43bcd1798a41" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_3e702d74-96c8-424c-a90d-3162365fc71a" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_d39fa7ce-200c-4e56-a455-43bcd1798a41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_bf2a0d3d-0841-4a7a-b860-35b7bcee0aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_d39fa7ce-200c-4e56-a455-43bcd1798a41" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_bf2a0d3d-0841-4a7a-b860-35b7bcee0aeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4c13a847-2b27-4cca-ab8d-5259c7ac12a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_98982b46-0cd0-4678-8aef-9d3268a2ba8d" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4c13a847-2b27-4cca-ab8d-5259c7ac12a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_4c13a847-2b27-4cca-ab8d-5259c7ac12a1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4c13a847-2b27-4cca-ab8d-5259c7ac12a1" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_4c13a847-2b27-4cca-ab8d-5259c7ac12a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_d4fadfe8-0ade-4ec8-a300-c4a388623c4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_4c13a847-2b27-4cca-ab8d-5259c7ac12a1" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_d4fadfe8-0ade-4ec8-a300-c4a388623c4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_ac588b5d-c91e-413a-94e3-be9896c3427d" xlink:href="vsec-20250630.xsd#vsec_FederalAndDefenseSegmentAndFleetSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_d4fadfe8-0ade-4ec8-a300-c4a388623c4d" xlink:to="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_ac588b5d-c91e-413a-94e3-be9896c3427d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_26050a59-f26d-44c8-8b87-ee0ed6fc37c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_26050a59-f26d-44c8-8b87-ee0ed6fc37c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_49832af6-d9e1-4721-948e-7ab933890750" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingExpense_49832af6-d9e1-4721-948e-7ab933890750" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_e2cadef4-6b86-4d4a-9b18-35f84356c290" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_e2cadef4-6b86-4d4a-9b18-35f84356c290" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationImpairmentExpense_df1bdba3-0d83-4073-9720-0a1aab8b4eaf" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationImpairmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationImpairmentExpense_df1bdba3-0d83-4073-9720-0a1aab8b4eaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_0cf96f10-2f5f-4206-ac4c-f19bc5b4ad9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_0cf96f10-2f5f-4206-ac4c-f19bc5b4ad9b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_867de055-ec0d-432a-896e-17917f7e817a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_867de055-ec0d-432a-896e-17917f7e817a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_ce959633-fda5-4b01-acb1-57f3e86a1ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_ce959633-fda5-4b01-acb1-57f3e86a1ad5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_68d1131b-8ab0-4af3-baaa-b81551840e70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b70b300f-8b07-47d0-9ec3-5a1102c91c89" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_68d1131b-8ab0-4af3-baaa-b81551840e70" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DiscontinuedOperationsBalanceSheetDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DiscontinuedOperationsBalanceSheetDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DiscontinuedOperationsBalanceSheetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_4476c9bf-2bd0-45a5-bffb-3b81f600d8f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_73b64d50-a74c-45a6-a0bb-1341edda5444" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_4476c9bf-2bd0-45a5-bffb-3b81f600d8f8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_73b64d50-a74c-45a6-a0bb-1341edda5444" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_4cd9650b-8ccb-4dd4-94a9-34993a97061f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_73b64d50-a74c-45a6-a0bb-1341edda5444" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_4cd9650b-8ccb-4dd4-94a9-34993a97061f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_4cd9650b-8ccb-4dd4-94a9-34993a97061f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_4cd9650b-8ccb-4dd4-94a9-34993a97061f" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_4cd9650b-8ccb-4dd4-94a9-34993a97061f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_3441bcba-63a0-47db-b373-4d64ccdc2131" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_4cd9650b-8ccb-4dd4-94a9-34993a97061f" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_3441bcba-63a0-47db-b373-4d64ccdc2131" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_5da4f46d-4d15-404b-9da8-a115eef6fe98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsHeldforsaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_3441bcba-63a0-47db-b373-4d64ccdc2131" xlink:to="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_5da4f46d-4d15-404b-9da8-a115eef6fe98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8dca5821-248e-4aff-bec0-63e520b9bca9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_73b64d50-a74c-45a6-a0bb-1341edda5444" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8dca5821-248e-4aff-bec0-63e520b9bca9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_8dca5821-248e-4aff-bec0-63e520b9bca9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8dca5821-248e-4aff-bec0-63e520b9bca9" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_8dca5821-248e-4aff-bec0-63e520b9bca9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_3ec0c071-0478-4860-bf97-d1df13f1749c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_8dca5821-248e-4aff-bec0-63e520b9bca9" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_3ec0c071-0478-4860-bf97-d1df13f1749c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_0174ae7d-058d-4965-a3c0-20467bf3d437" xlink:href="vsec-20250630.xsd#vsec_FederalAndDefenseSegmentAndFleetSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_3ec0c071-0478-4860-bf97-d1df13f1749c" xlink:to="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_0174ae7d-058d-4965-a3c0-20467bf3d437" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_4476c9bf-2bd0-45a5-bffb-3b81f600d8f8" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationCashOverdraft_b2b18c17-2b33-419a-a41f-64cb95fbe9b2" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationCashOverdraft"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationCashOverdraft_b2b18c17-2b33-419a-a41f-64cb95fbe9b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet_b6987f30-dfbd-478e-81c7-de2d2e98bbbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet_b6987f30-dfbd-478e-81c7-de2d2e98bbbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_91a98ff6-af62-436a-8635-165c9b48057e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory1_91a98ff6-af62-436a-8635-165c9b48057e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssetsCurrent_b6fcb8fe-ec40-4a7f-b57b-c82d9358f4a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPrepaidAndOtherAssetsCurrent_b6fcb8fe-ec40-4a7f-b57b-c82d9358f4a0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentNoncurrent_31fa2977-2cfc-432c-9471-aecd0d1bebcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentNoncurrent_31fa2977-2cfc-432c-9471-aecd0d1bebcf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets_2af3107b-dd33-459a-97a9-f413b10d8cc1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets_2af3107b-dd33-459a-97a9-f413b10d8cc1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_6cf1e59d-e9b9-47c4-934f-e4d3954f87c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_6cf1e59d-e9b9-47c4-934f-e4d3954f87c6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseRightOfUseAssets_41542971-d238-4222-9021-0d46691bf2cd" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseRightOfUseAssets_41542971-d238-4222-9021-0d46691bf2cd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets_f69a2a8a-d5b5-4aaa-bd92-febe98459527" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets_f69a2a8a-d5b5-4aaa-bd92-febe98459527" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_1717dd75-2769-4bf1-8586-33e908890e6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperationAbstract_5b7eff77-46b0-42fd-a58d-b7f4b79c7c28" xlink:to="loc_us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_1717dd75-2769-4bf1-8586-33e908890e6f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_4476c9bf-2bd0-45a5-bffb-3b81f600d8f8" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable_d1358a28-686f-4802-a478-d72999963fd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable_d1358a28-686f-4802-a478-d72999963fd6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities_ae2246d7-3855-4d62-8287-e1a93ce7377c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities_ae2246d7-3855-4d62-8287-e1a93ce7377c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseLiabilities_227035af-8422-4e8c-91b7-dafdc75bdc03" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationOperatingLeaseLiabilities_227035af-8422-4e8c-91b7-dafdc75bdc03" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities_cf665604-9316-4e23-bcd0-1e414ac69438" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDeferredTaxLiabilities_cf665604-9316-4e23-bcd0-1e414ac69438" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_31b23da5-9084-4828-8891-d5b1bdbe4256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationAbstract_e758af31-e509-41b2-bec6-8d929086a6a5" xlink:to="loc_us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation_31b23da5-9084-4828-8891-d5b1bdbe4256" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DiscontinuedOperationsCashFlowsStatementDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DiscontinuedOperationsCashFlowsStatementDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DiscontinuedOperationsCashFlowsStatementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7ed2ab10-7ede-4cd9-8950-ffb9e34a6a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b233fa0e-49eb-4d86-ad69-2483c68d9575" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7ed2ab10-7ede-4cd9-8950-ffb9e34a6a6f" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b233fa0e-49eb-4d86-ad69-2483c68d9575" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_db11fc86-2192-4fde-9679-f5c5c2d8da6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b233fa0e-49eb-4d86-ad69-2483c68d9575" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_db11fc86-2192-4fde-9679-f5c5c2d8da6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_db11fc86-2192-4fde-9679-f5c5c2d8da6c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_db11fc86-2192-4fde-9679-f5c5c2d8da6c" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_db11fc86-2192-4fde-9679-f5c5c2d8da6c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a6496925-136e-41e1-8ab6-fdc099d4733e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_db11fc86-2192-4fde-9679-f5c5c2d8da6c" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a6496925-136e-41e1-8ab6-fdc099d4733e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_e699bb32-8c8a-4663-a0d6-e46a50e10bf6" xlink:href="vsec-20250630.xsd#vsec_FederalAndDefenseSegmentAndFleetSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_a6496925-136e-41e1-8ab6-fdc099d4733e" xlink:to="loc_vsec_FederalAndDefenseSegmentAndFleetSegmentMember_e699bb32-8c8a-4663-a0d6-e46a50e10bf6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_d252f2cf-8098-4e83-8575-045b3f975727" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_b233fa0e-49eb-4d86-ad69-2483c68d9575" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_d252f2cf-8098-4e83-8575-045b3f975727" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_d252f2cf-8098-4e83-8575-045b3f975727_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d252f2cf-8098-4e83-8575-045b3f975727" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_d252f2cf-8098-4e83-8575-045b3f975727_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_55af903c-03b0-4b80-a7df-10239aedd487" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_d252f2cf-8098-4e83-8575-045b3f975727" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_55af903c-03b0-4b80-a7df-10239aedd487" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_b100666b-2978-4bea-8a84-12c71d8c47d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsHeldforsaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_55af903c-03b0-4b80-a7df-10239aedd487" xlink:to="loc_us-gaap_DiscontinuedOperationsHeldforsaleMember_b100666b-2978-4bea-8a84-12c71d8c47d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_cbd1c318-548b-40c4-8bd4-1177db165f60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7ed2ab10-7ede-4cd9-8950-ffb9e34a6a6f" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_cbd1c318-548b-40c4-8bd4-1177db165f60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationStockBasedCompensation_5e3bbecd-047d-464b-9cc0-191eeeb80934" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationStockBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7ed2ab10-7ede-4cd9-8950-ffb9e34a6a6f" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationStockBasedCompensation_5e3bbecd-047d-464b-9cc0-191eeeb80934" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationPaymentsForPropertyPlantAndEquipment_da083c77-bf8d-4b89-8d29-96af76caac2a" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationPaymentsForPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7ed2ab10-7ede-4cd9-8950-ffb9e34a6a6f" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationPaymentsForPropertyPlantAndEquipment_da083c77-bf8d-4b89-8d29-96af76caac2a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#RevenueDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_ff7be4d0-bd5f-4010-bb36-835c5cbe85b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_ff7be4d0-bd5f-4010-bb36-835c5cbe85b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ff7be4d0-bd5f-4010-bb36-835c5cbe85b6" xlink:to="loc_srt_MajorCustomersAxis_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5" xlink:to="loc_srt_NameOfMajorCustomerDomain_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_b4369ab0-c717-4b64-9c06-216b14d8bad5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_aed3cfeb-49b5-4f7f-a3aa-29e3ee08e0f5" xlink:to="loc_srt_NameOfMajorCustomerDomain_b4369ab0-c717-4b64-9c06-216b14d8bad5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_CommercialMember_d5c7c40d-9955-47c8-931a-3943a740d405" xlink:href="vsec-20250630.xsd#vsec_CommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_b4369ab0-c717-4b64-9c06-216b14d8bad5" xlink:to="loc_vsec_CommercialMember_d5c7c40d-9955-47c8-931a-3943a740d405" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_OtherGovernmentMember_a2bef95f-5759-4d17-a02a-3257916bcbba" xlink:href="vsec-20250630.xsd#vsec_OtherGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_b4369ab0-c717-4b64-9c06-216b14d8bad5" xlink:to="loc_vsec_OtherGovernmentMember_a2bef95f-5759-4d17-a02a-3257916bcbba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_ff7be4d0-bd5f-4010-bb36-835c5cbe85b6" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0e72698d-01dc-48af-95b6-a16e5bc389ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_0d0298cc-7ae1-463e-a7f0-8e9483b56bdb" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0e72698d-01dc-48af-95b6-a16e5bc389ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_RepairMember_958b7c49-4a79-43ba-82ec-3a2786983951" xlink:href="vsec-20250630.xsd#vsec_RepairMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0e72698d-01dc-48af-95b6-a16e5bc389ea" xlink:to="loc_vsec_RepairMember_958b7c49-4a79-43ba-82ec-3a2786983951" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DistributionMember_82449871-7ba5-45ac-bb69-6d19e7691e17" xlink:href="vsec-20250630.xsd#vsec_DistributionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_0e72698d-01dc-48af-95b6-a16e5bc389ea" xlink:to="loc_vsec_DistributionMember_82449871-7ba5-45ac-bb69-6d19e7691e17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a9b6ed4e-0d2a-4c48-aca7-43d52fcbb2c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a9b6ed4e-0d2a-4c48-aca7-43d52fcbb2c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_13575bb8-d689-4145-a155-fac7327002ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_13575bb8-d689-4145-a155-fac7327002ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_42c556f4-fe1a-46c7-8c76-5187578da718" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_42c556f4-fe1a-46c7-8c76-5187578da718" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_6f46e549-2e9e-4d64-9475-b9897f12fcde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_6b3342f6-242b-4546-a498-cb9d8bb4d1f0" xlink:to="loc_us-gaap_ContractWithCustomerLiability_6f46e549-2e9e-4d64-9475-b9897f12fcde" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DebtLongTermdebtDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DebtLongTermdebtDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DebtLongTermdebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_982e850e-584a-4367-9270-46b6a24cdf31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_DebtInstrumentTable_982e850e-584a-4367-9270-46b6a24cdf31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_c16dde1b-bb28-49c2-bf07-d7c83cb035eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_982e850e-584a-4367-9270-46b6a24cdf31" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_c16dde1b-bb28-49c2-bf07-d7c83cb035eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c16dde1b-bb28-49c2-bf07-d7c83cb035eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c16dde1b-bb28-49c2-bf07-d7c83cb035eb" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c16dde1b-bb28-49c2-bf07-d7c83cb035eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e532b400-5bc6-48d6-bb12-8695884135e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c16dde1b-bb28-49c2-bf07-d7c83cb035eb" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e532b400-5bc6-48d6-bb12-8695884135e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_dfd1b84e-06f8-43af-8c06-c29b52a6f5d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e532b400-5bc6-48d6-bb12-8695884135e5" xlink:to="loc_us-gaap_LoansPayableMember_dfd1b84e-06f8-43af-8c06-c29b52a6f5d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_93c7ddb6-5b01-4b3d-a668-ad18808f8df2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e532b400-5bc6-48d6-bb12-8695884135e5" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_93c7ddb6-5b01-4b3d-a668-ad18808f8df2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_d993fec4-0652-4fda-8c23-9057a3a00e73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_d993fec4-0652-4fda-8c23-9057a3a00e73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_bb28b5f5-0fc9-44a4-be6f-2681d2b75326" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_bb28b5f5-0fc9-44a4-be6f-2681d2b75326" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_9d23f465-5b05-4454-ab89-1a75797693a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_LongTermDebt_9d23f465-5b05-4454-ab89-1a75797693a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_88ecf7eb-9061-4d44-b0f2-e86fb0b191c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_LongTermDebtCurrent_88ecf7eb-9061-4d44-b0f2-e86fb0b191c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_ee9dedd7-c063-4fdc-a121-ede7bf467ed9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_80e0f329-d20d-45c9-a69c-ae9dc6ce7301" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_ee9dedd7-c063-4fdc-a121-ede7bf467ed9" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_45e36e39-7bce-4f67-bb30-27ab80acf1b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_45e36e39-7bce-4f67-bb30-27ab80acf1b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_45e36e39-7bce-4f67-bb30-27ab80acf1b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_45e36e39-7bce-4f67-bb30-27ab80acf1b9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_45e36e39-7bce-4f67-bb30-27ab80acf1b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c653bc3f-b173-4e49-9658-5aab5e103064" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_45e36e39-7bce-4f67-bb30-27ab80acf1b9" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c653bc3f-b173-4e49-9658-5aab5e103064" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_2e850800-368e-420b-8b2b-171f5cfb34e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c653bc3f-b173-4e49-9658-5aab5e103064" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_2e850800-368e-420b-8b2b-171f5cfb34e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_abdcc030-457c-44ad-8b6a-963ad19cb127" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c653bc3f-b173-4e49-9658-5aab5e103064" xlink:to="loc_us-gaap_LoansPayableMember_abdcc030-457c-44ad-8b6a-963ad19cb127" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_68db99f8-2f95-4055-a7d4-0c05cd6bc650" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:to="loc_us-gaap_VariableRateAxis_68db99f8-2f95-4055-a7d4-0c05cd6bc650" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_68db99f8-2f95-4055-a7d4-0c05cd6bc650_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_68db99f8-2f95-4055-a7d4-0c05cd6bc650" xlink:to="loc_us-gaap_VariableRateDomain_68db99f8-2f95-4055-a7d4-0c05cd6bc650_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_68db99f8-2f95-4055-a7d4-0c05cd6bc650" xlink:to="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_5d46607f-2960-4117-a090-670fcd1594f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_5d46607f-2960-4117-a090-670fcd1594f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DailySecuredOvernightFinancingRateMember_b37283c8-86b9-4a18-b27c-f2f924469813" xlink:href="vsec-20250630.xsd#vsec_DailySecuredOvernightFinancingRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:to="loc_vsec_DailySecuredOvernightFinancingRateMember_b37283c8-86b9-4a18-b27c-f2f924469813" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_0474ad42-e7e0-4b11-8766-833e374a2649" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_0474ad42-e7e0-4b11-8766-833e374a2649" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_aa243707-cd2c-40b3-afb0-7288152f297d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_def66c38-9668-4cf8-aeae-4fd1c9f01927" xlink:to="loc_us-gaap_BaseRateMember_aa243707-cd2c-40b3-afb0-7288152f297d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_b2c16527-83c3-400d-a4e6-6dfbc6885466" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:to="loc_srt_RangeAxis_b2c16527-83c3-400d-a4e6-6dfbc6885466" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b2c16527-83c3-400d-a4e6-6dfbc6885466_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_b2c16527-83c3-400d-a4e6-6dfbc6885466" xlink:to="loc_srt_RangeMember_b2c16527-83c3-400d-a4e6-6dfbc6885466_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4d242c81-8f5f-4b0a-b720-3b5c58a38a70" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_b2c16527-83c3-400d-a4e6-6dfbc6885466" xlink:to="loc_srt_RangeMember_4d242c81-8f5f-4b0a-b720-3b5c58a38a70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_7b58d16a-ac96-432f-a262-61d12a929259" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d242c81-8f5f-4b0a-b720-3b5c58a38a70" xlink:to="loc_srt_MinimumMember_7b58d16a-ac96-432f-a262-61d12a929259" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_dc36dbf1-7cd9-48ce-831e-170e129be2c1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d242c81-8f5f-4b0a-b720-3b5c58a38a70" xlink:to="loc_srt_MaximumMember_dc36dbf1-7cd9-48ce-831e-170e129be2c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_5776d153-93aa-4134-a8c7-bf58d949be2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_32ac2f2b-79ff-4e76-94be-e844fcd4dfc8" xlink:to="loc_us-gaap_CreditFacilityAxis_5776d153-93aa-4134-a8c7-bf58d949be2b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5776d153-93aa-4134-a8c7-bf58d949be2b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_5776d153-93aa-4134-a8c7-bf58d949be2b" xlink:to="loc_us-gaap_CreditFacilityDomain_5776d153-93aa-4134-a8c7-bf58d949be2b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_fa20bd77-2631-44cc-810f-5dd6f3693672" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_5776d153-93aa-4134-a8c7-bf58d949be2b" xlink:to="loc_us-gaap_CreditFacilityDomain_fa20bd77-2631-44cc-810f-5dd6f3693672" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_676d7848-424c-4b30-b59d-0b095c7c7aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_fa20bd77-2631-44cc-810f-5dd6f3693672" xlink:to="loc_us-gaap_LineOfCreditMember_676d7848-424c-4b30-b59d-0b095c7c7aa8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_73db6ebd-f548-402c-9715-2f707108a118" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_fa20bd77-2631-44cc-810f-5dd6f3693672" xlink:to="loc_us-gaap_LetterOfCreditMember_73db6ebd-f548-402c-9715-2f707108a118" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_81a49a59-b9e3-414a-80f5-78c7893f72d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_fa20bd77-2631-44cc-810f-5dd6f3693672" xlink:to="loc_us-gaap_SecuredDebtMember_81a49a59-b9e3-414a-80f5-78c7893f72d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_2f46d648-e9c9-4dc4-84e2-e3664bfa762a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_2f46d648-e9c9-4dc4-84e2-e3664bfa762a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c31e9ebd-25d4-47f6-811b-9f40f894c4b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c31e9ebd-25d4-47f6-811b-9f40f894c4b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_0bfa7817-a017-4de3-a39c-928d8fff4e29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_0bfa7817-a017-4de3-a39c-928d8fff4e29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_6f1692c0-f480-456c-97a6-19e863d9f413" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_6f1692c0-f480-456c-97a6-19e863d9f413" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFeeAmount_d2eecedc-c27b-4384-bcfe-d2d086d45f4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DebtInstrumentFeeAmount_d2eecedc-c27b-4384-bcfe-d2d086d45f4c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_f89aab5e-be5b-4696-9610-4e4c7bb16001" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_f89aab5e-be5b-4696-9610-4e4c7bb16001" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_727f13a2-5a23-409a-bb80-838a252095ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_727f13a2-5a23-409a-bb80-838a252095ff" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_ef19c609-ada3-4e23-accd-fd73a7a78e10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_ef19c609-ada3-4e23-accd-fd73a7a78e10" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_9f90a9b9-c784-441d-a6d6-c28875096755" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_74fb33f0-a093-408c-a024-3c29a8a33477" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_9f90a9b9-c784-441d-a6d6-c28875096755" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DebtLoanPaymentsDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DebtLoanPaymentsDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DebtLoanPaymentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b7f70ef2-a73b-4798-a9dd-69cc762f1bc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_DebtInstrumentTable_b7f70ef2-a73b-4798-a9dd-69cc762f1bc7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_49001240-7abd-4d55-8890-bc403e0cd262" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b7f70ef2-a73b-4798-a9dd-69cc762f1bc7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_49001240-7abd-4d55-8890-bc403e0cd262" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_49001240-7abd-4d55-8890-bc403e0cd262_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_49001240-7abd-4d55-8890-bc403e0cd262" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_49001240-7abd-4d55-8890-bc403e0cd262_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_35067f3d-9919-4e18-a195-865b0b8fd2ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_49001240-7abd-4d55-8890-bc403e0cd262" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_35067f3d-9919-4e18-a195-865b0b8fd2ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_TermLoanMember_b534f56a-9829-4c66-a0c3-48b21439bc95" xlink:href="vsec-20250630.xsd#vsec_TermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_35067f3d-9919-4e18-a195-865b0b8fd2ae" xlink:to="loc_vsec_TermLoanMember_b534f56a-9829-4c66-a0c3-48b21439bc95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_38dbbfac-4f62-422d-bca3-941164cbbfbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_35067f3d-9919-4e18-a195-865b0b8fd2ae" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_38dbbfac-4f62-422d-bca3-941164cbbfbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_2aea9dd2-9f24-4f82-be79-01908987db1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalRemainderOfFiscalYear_2aea9dd2-9f24-4f82-be79-01908987db1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_13535e57-31f8-48cb-b3eb-b5530fd4fecb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_13535e57-31f8-48cb-b3eb-b5530fd4fecb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_0948561e-60c7-4d03-beaa-baab4471eacb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_0948561e-60c7-4d03-beaa-baab4471eacb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_752dd48f-5b22-421b-8bf2-1fc5f03f9426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_752dd48f-5b22-421b-8bf2-1fc5f03f9426" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_651bf7d7-7c79-41c4-b626-9b33122d8720" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_651bf7d7-7c79-41c4-b626-9b33122d8720" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_feb8febc-9750-4461-990f-a0e848223220" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_feb8febc-9750-4461-990f-a0e848223220" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_0b3e1dda-e5ba-4982-8ed6-1b0836fde5c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_c412a540-7230-4dcc-a3b3-0cd201f787c0" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_0b3e1dda-e5ba-4982-8ed6-1b0836fde5c3" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/DerivativeInstrumentsandHedgingActivitiesDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#DerivativeInstrumentsandHedgingActivitiesDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/DerivativeInstrumentsandHedgingActivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_5c4c29f3-0ca5-4f6b-9c2b-74c8c72d11c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e5f3f52f-f979-443c-8515-7f60ad39f71b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_5c4c29f3-0ca5-4f6b-9c2b-74c8c72d11c3" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e5f3f52f-f979-443c-8515-7f60ad39f71b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_0f8d493c-0885-4c93-a5de-c37723af30e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e5f3f52f-f979-443c-8515-7f60ad39f71b" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_0f8d493c-0885-4c93-a5de-c37723af30e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_0f8d493c-0885-4c93-a5de-c37723af30e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_0f8d493c-0885-4c93-a5de-c37723af30e7" xlink:to="loc_us-gaap_HedgingRelationshipDomain_0f8d493c-0885-4c93-a5de-c37723af30e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingRelationshipDomain_ee0a4cac-af1e-4b4b-960e-bf1a250eef1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingRelationshipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis_0f8d493c-0885-4c93-a5de-c37723af30e7" xlink:to="loc_us-gaap_HedgingRelationshipDomain_ee0a4cac-af1e-4b4b-960e-bf1a250eef1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowHedgingMember_e8464eb6-6da1-4e87-8595-03a2e39937d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashFlowHedgingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingRelationshipDomain_ee0a4cac-af1e-4b4b-960e-bf1a250eef1d" xlink:to="loc_us-gaap_CashFlowHedgingMember_e8464eb6-6da1-4e87-8595-03a2e39937d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_aa7430ce-a895-4056-b51f-49f42adec3fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e5f3f52f-f979-443c-8515-7f60ad39f71b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_aa7430ce-a895-4056-b51f-49f42adec3fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_aa7430ce-a895-4056-b51f-49f42adec3fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_aa7430ce-a895-4056-b51f-49f42adec3fe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_aa7430ce-a895-4056-b51f-49f42adec3fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_31a25e93-58d5-46ce-b935-cfef12e13318" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_aa7430ce-a895-4056-b51f-49f42adec3fe" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_31a25e93-58d5-46ce-b935-cfef12e13318" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_InterestRateSwap28Member_070f49a3-54a3-4615-be62-a01bfb90955e" xlink:href="vsec-20250630.xsd#vsec_InterestRateSwap28Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_31a25e93-58d5-46ce-b935-cfef12e13318" xlink:to="loc_vsec_InterestRateSwap28Member_070f49a3-54a3-4615-be62-a01bfb90955e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_InterestRateSwap45Member_5e70025b-6474-4067-96f9-868b90b0232f" xlink:href="vsec-20250630.xsd#vsec_InterestRateSwap45Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_31a25e93-58d5-46ce-b935-cfef12e13318" xlink:to="loc_vsec_InterestRateSwap45Member_5e70025b-6474-4067-96f9-868b90b0232f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_d39ea2a8-feb9-40a1-b7f0-f7c508ea6535" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_5c4c29f3-0ca5-4f6b-9c2b-74c8c72d11c3" xlink:to="loc_us-gaap_DerivativeNotionalAmount_d39ea2a8-feb9-40a1-b7f0-f7c508ea6535" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_73d1667f-a9d2-42f7-86db-320ef1f3954d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_5c4c29f3-0ca5-4f6b-9c2b-74c8c72d11c3" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_73d1667f-a9d2-42f7-86db-320ef1f3954d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTaxParent_70b4a7d6-ffdf-43bb-b481-351a92af8dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTaxParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_5c4c29f3-0ca5-4f6b-9c2b-74c8c72d11c3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationTaxParent_70b4a7d6-ffdf-43bb-b481-351a92af8dcf" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/BusinessSegmentSegmentInformationDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#BusinessSegmentSegmentInformationDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/BusinessSegmentSegmentInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4cb26ee8-b924-484a-a7e2-0746e0d5b722" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4cb26ee8-b924-484a-a7e2-0746e0d5b722" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_1fdec687-4292-46b9-af11-6bc537f07594" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4cb26ee8-b924-484a-a7e2-0746e0d5b722" xlink:to="loc_srt_ConsolidationItemsAxis_1fdec687-4292-46b9-af11-6bc537f07594" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_1fdec687-4292-46b9-af11-6bc537f07594_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_1fdec687-4292-46b9-af11-6bc537f07594" xlink:to="loc_srt_ConsolidationItemsDomain_1fdec687-4292-46b9-af11-6bc537f07594_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_93c6283e-3c21-4a16-8546-f71cf8514f38" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_1fdec687-4292-46b9-af11-6bc537f07594" xlink:to="loc_srt_ConsolidationItemsDomain_93c6283e-3c21-4a16-8546-f71cf8514f38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_7d8839c5-afb8-4a58-a55e-8e02d3bdeb95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_93c6283e-3c21-4a16-8546-f71cf8514f38" xlink:to="loc_us-gaap_OperatingSegmentsMember_7d8839c5-afb8-4a58-a55e-8e02d3bdeb95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_8734dee2-464c-452a-ba6a-75b899b476d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_93c6283e-3c21-4a16-8546-f71cf8514f38" xlink:to="loc_us-gaap_CorporateNonSegmentMember_8734dee2-464c-452a-ba6a-75b899b476d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_4cb26ee8-b924-484a-a7e2-0746e0d5b722" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68" xlink:to="loc_us-gaap_SegmentDomain_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_92865c2e-bded-4b56-ab21-655754adb543" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b11989fa-89a5-4e2d-8e48-ec7f7ee19d68" xlink:to="loc_us-gaap_SegmentDomain_92865c2e-bded-4b56-ab21-655754adb543" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_AviationSegmentMember_843b8a59-bbe4-44ca-9cf9-1b74085c9dda" xlink:href="vsec-20250630.xsd#vsec_AviationSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_92865c2e-bded-4b56-ab21-655754adb543" xlink:to="loc_vsec_AviationSegmentMember_843b8a59-bbe4-44ca-9cf9-1b74085c9dda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_831403f2-2967-4b78-acc1-abbb7c92f8f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_831403f2-2967-4b78-acc1-abbb7c92f8f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_435fda23-9dff-4164-ad33-ff7d99d10cf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_435fda23-9dff-4164-ad33-ff7d99d10cf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_SegmentReportingDepreciationDepletionAndAmortization_22a17180-aac8-41fa-9170-cd4398db918f" xlink:href="vsec-20250630.xsd#vsec_SegmentReportingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_vsec_SegmentReportingDepreciationDepletionAndAmortization_22a17180-aac8-41fa-9170-cd4398db918f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_AllocatedCorporateCost_c526d5d9-0b5a-4f9b-86ba-33c35d34a4b0" xlink:href="vsec-20250630.xsd#vsec_AllocatedCorporateCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_vsec_AllocatedCorporateCost_c526d5d9-0b5a-4f9b-86ba-33c35d34a4b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_UnallocatedCorporateCosts_c70b8ac4-ad6b-4c1c-9ee9-25202b5c2d52" xlink:href="vsec-20250630.xsd#vsec_UnallocatedCorporateCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_vsec_UnallocatedCorporateCosts_c70b8ac4-ad6b-4c1c-9ee9-25202b5c2d52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_82c1b57d-7157-453d-a5dc-8eea642f3176" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_OperatingIncomeLoss_82c1b57d-7157-453d-a5dc-8eea642f3176" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_4ee651db-b752-4168-be38-be7fd3df0409" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_4ee651db-b752-4168-be38-be7fd3df0409" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_7756da43-1080-400a-bec8-c912915e42a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_7756da43-1080-400a-bec8-c912915e42a7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_bd5b8641-bfa3-4ad3-8616-fb23d042c97e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_bd5b8641-bfa3-4ad3-8616-fb23d042c97e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_dbb3a530-9d7b-42cf-aca5-e9aa3a484e50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_94737fd3-c60f-4450-931a-f6f748a88eb6" xlink:to="loc_us-gaap_NetIncomeLoss_dbb3a530-9d7b-42cf-aca5-e9aa3a484e50" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/GoodwillandIntangibleAssetsIntangibleAssetsDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#GoodwillandIntangibleAssetsIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/GoodwillandIntangibleAssetsIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_128dc788-84df-4f71-9f66-f29af9d35464" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fbac217d-6a8d-4f94-91de-9bb071c4bae5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_128dc788-84df-4f71-9f66-f29af9d35464" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fbac217d-6a8d-4f94-91de-9bb071c4bae5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a285cf62-4a94-40df-a68f-f45a12dde249" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fbac217d-6a8d-4f94-91de-9bb071c4bae5" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a285cf62-4a94-40df-a68f-f45a12dde249" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a285cf62-4a94-40df-a68f-f45a12dde249_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a285cf62-4a94-40df-a68f-f45a12dde249" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a285cf62-4a94-40df-a68f-f45a12dde249_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5c198602-c38c-4f03-a270-14e1440947ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a285cf62-4a94-40df-a68f-f45a12dde249" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5c198602-c38c-4f03-a270-14e1440947ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractualRightsMember_8612fe85-c99a-4d50-a082-63a67081492d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractualRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5c198602-c38c-4f03-a270-14e1440947ba" xlink:to="loc_us-gaap_ContractualRightsMember_8612fe85-c99a-4d50-a082-63a67081492d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_edfbd7fd-48ab-43b8-83b2-d121518d7c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_5c198602-c38c-4f03-a270-14e1440947ba" xlink:to="loc_us-gaap_TradeNamesMember_edfbd7fd-48ab-43b8-83b2-d121518d7c1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_79111a8c-0748-4961-abc5-a8536480228a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_128dc788-84df-4f71-9f66-f29af9d35464" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_79111a8c-0748-4961-abc5-a8536480228a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_fa77ef1c-0a56-4ad5-ac6f-78c903747138" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_128dc788-84df-4f71-9f66-f29af9d35464" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_fa77ef1c-0a56-4ad5-ac6f-78c903747138" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8a07d7ed-7446-4a4f-a5ac-b1195ba5f6f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_128dc788-84df-4f71-9f66-f29af9d35464" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_8a07d7ed-7446-4a4f-a5ac-b1195ba5f6f0" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#FairValueMeasurementsFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/FairValueMeasurementsFinancialAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_24ae26e2-6dc6-4bd8-a5b8-e6f21b90635b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_495a5f87-dd1e-405d-a528-076fd75ab152" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_24ae26e2-6dc6-4bd8-a5b8-e6f21b90635b" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_495a5f87-dd1e-405d-a528-076fd75ab152" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_495a5f87-dd1e-405d-a528-076fd75ab152" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_07e33cc5-aa6a-4bad-a07c-2975e4b735e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_44cc9e57-b8a6-48f9-9a83-bc6e497ea09c" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_07e33cc5-aa6a-4bad-a07c-2975e4b735e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_72867d1a-b358-4b09-9518-e00cd9cbae7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_07e33cc5-aa6a-4bad-a07c-2975e4b735e1" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_72867d1a-b358-4b09-9518-e00cd9cbae7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_495a5f87-dd1e-405d-a528-076fd75ab152" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9037f291-1d5e-453e-91f9-bd712872abef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_bffa5b4b-0381-45e2-9b39-0c30dc4a54b8" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9037f291-1d5e-453e-91f9-bd712872abef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_e41bb14c-8037-4108-b020-b28a9a1b3be6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9037f291-1d5e-453e-91f9-bd712872abef" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_e41bb14c-8037-4108-b020-b28a9a1b3be6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_42afb373-7844-4a16-bf74-66e8d782c999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9037f291-1d5e-453e-91f9-bd712872abef" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_42afb373-7844-4a16-bf74-66e8d782c999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_abf56d1e-e4f4-4e0a-8f30-c167656aafc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9037f291-1d5e-453e-91f9-bd712872abef" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_abf56d1e-e4f4-4e0a-8f30-c167656aafc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_MutualFundsHeldInDeferredSupplementalCompensationPlanFairValueDisclosure_3bf27d77-aed7-4e5f-9c0e-3ac5bff24c41" xlink:href="vsec-20250630.xsd#vsec_MutualFundsHeldInDeferredSupplementalCompensationPlanFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_24ae26e2-6dc6-4bd8-a5b8-e6f21b90635b" xlink:to="loc_vsec_MutualFundsHeldInDeferredSupplementalCompensationPlanFairValueDisclosure_3bf27d77-aed7-4e5f-9c0e-3ac5bff24c41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateDerivativeLiabilitiesAtFairValue_1575abb9-2d41-4105-9029-c4541a88a634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateDerivativeLiabilitiesAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_24ae26e2-6dc6-4bd8-a5b8-e6f21b90635b" xlink:to="loc_us-gaap_InterestRateDerivativeLiabilitiesAtFairValue_1575abb9-2d41-4105-9029-c4541a88a634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesFairValueDisclosure_e6853225-233a-4392-87fc-48c6ab8a009a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivablesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_24ae26e2-6dc6-4bd8-a5b8-e6f21b90635b" xlink:to="loc_us-gaap_ReceivablesFairValueDisclosure_e6853225-233a-4392-87fc-48c6ab8a009a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#FairValueMeasurementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/FairValueMeasurementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c244ac35-255c-4ff5-b580-873c2ee02863" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c244ac35-255c-4ff5-b580-873c2ee02863" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_f6d62593-cd4e-424a-a894-db43eaf67f72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_f6d62593-cd4e-424a-a894-db43eaf67f72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_f6d62593-cd4e-424a-a894-db43eaf67f72_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_f6d62593-cd4e-424a-a894-db43eaf67f72" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_f6d62593-cd4e-424a-a894-db43eaf67f72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_0c80ca1c-1715-456e-91f6-1adfac8438eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_f6d62593-cd4e-424a-a894-db43eaf67f72" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_0c80ca1c-1715-456e-91f6-1adfac8438eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_1ab9a270-69f5-491f-8a0f-e6d2592c8371" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_0c80ca1c-1715-456e-91f6-1adfac8438eb" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_1ab9a270-69f5-491f-8a0f-e6d2592c8371" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_d8544352-9821-4c78-92c5-2c79d9855f34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_d8544352-9821-4c78-92c5-2c79d9855f34" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_d8544352-9821-4c78-92c5-2c79d9855f34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_d8544352-9821-4c78-92c5-2c79d9855f34" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_d8544352-9821-4c78-92c5-2c79d9855f34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1b055b8-eb7e-4ba3-9c8f-077a3da7baa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_d8544352-9821-4c78-92c5-2c79d9855f34" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1b055b8-eb7e-4ba3-9c8f-077a3da7baa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FleetSaleMember_059061e2-f229-44ab-b298-2d0d28ab4429" xlink:href="vsec-20250630.xsd#vsec_FleetSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1b055b8-eb7e-4ba3-9c8f-077a3da7baa4" xlink:to="loc_vsec_FleetSaleMember_059061e2-f229-44ab-b298-2d0d28ab4429" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_890e9bed-6752-4261-b2b6-2966e2bc2365" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_890e9bed-6752-4261-b2b6-2966e2bc2365" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_890e9bed-6752-4261-b2b6-2966e2bc2365_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_890e9bed-6752-4261-b2b6-2966e2bc2365" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_890e9bed-6752-4261-b2b6-2966e2bc2365_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ef3cf75c-bedc-4c31-bbf1-847bd01e2c49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_890e9bed-6752-4261-b2b6-2966e2bc2365" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ef3cf75c-bedc-4c31-bbf1-847bd01e2c49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_d2f8c9ea-c7c0-4a4b-a9d4-5e40245774f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ef3cf75c-bedc-4c31-bbf1-847bd01e2c49" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_d2f8c9ea-c7c0-4a4b-a9d4-5e40245774f9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_6143c548-2902-4d71-a422-cf7cfe4be0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d93b7c2f-57d3-4a8d-8acb-14e54d375986" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_6143c548-2902-4d71-a422-cf7cfe4be0a9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_6143c548-2902-4d71-a422-cf7cfe4be0a9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_6143c548-2902-4d71-a422-cf7cfe4be0a9" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_6143c548-2902-4d71-a422-cf7cfe4be0a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_fa26d78e-a3bb-4d10-b731-4ebfcc4a7706" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_6143c548-2902-4d71-a422-cf7cfe4be0a9" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_fa26d78e-a3bb-4d10-b731-4ebfcc4a7706" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_46338289-5778-4abd-8359-4ea2b664ccab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_fa26d78e-a3bb-4d10-b731-4ebfcc4a7706" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_46338289-5778-4abd-8359-4ea2b664ccab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_ccfa4643-d59c-4604-af94-65634389a552" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_fa26d78e-a3bb-4d10-b731-4ebfcc4a7706" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_ccfa4643-d59c-4604-af94-65634389a552" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_56b68308-dbdb-4299-b779-4732dea3e9a6" xlink:href="vsec-20250630.xsd#vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c244ac35-255c-4ff5-b580-873c2ee02863" xlink:to="loc_vsec_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_56b68308-dbdb-4299-b779-4732dea3e9a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AlternativeInvestmentMeasurementInput_40aefe9b-9931-47fd-9257-fd3a08556b7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AlternativeInvestmentMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c244ac35-255c-4ff5-b580-873c2ee02863" xlink:to="loc_us-gaap_AlternativeInvestmentMeasurementInput_40aefe9b-9931-47fd-9257-fd3a08556b7d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/FairValueMeasurementsChangesintheFairValueoftheEarnOutReceivableDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#FairValueMeasurementsChangesintheFairValueoftheEarnOutReceivableDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/FairValueMeasurementsChangesintheFairValueoftheEarnOutReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_949b8852-adb4-4777-a494-ac5f206bc8c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_e961ae2e-93a5-4781-9d78-0ac9631cc22f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_949b8852-adb4-4777-a494-ac5f206bc8c1" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_e961ae2e-93a5-4781-9d78-0ac9631cc22f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44b85819-3f38-4533-913e-b6fa9ca9c501" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_e961ae2e-93a5-4781-9d78-0ac9631cc22f" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44b85819-3f38-4533-913e-b6fa9ca9c501" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_44b85819-3f38-4533-913e-b6fa9ca9c501_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44b85819-3f38-4533-913e-b6fa9ca9c501" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_44b85819-3f38-4533-913e-b6fa9ca9c501_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_37c53e65-c1f0-49cc-89a4-a9921ccbcd3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_44b85819-3f38-4533-913e-b6fa9ca9c501" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_37c53e65-c1f0-49cc-89a4-a9921ccbcd3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_b1b1e1f9-41f7-48d6-b915-a92b5a2eefaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_37c53e65-c1f0-49cc-89a4-a9921ccbcd3e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_b1b1e1f9-41f7-48d6-b915-a92b5a2eefaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bf37b70c-fc82-47a4-9ef9-6099e8519aa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_e961ae2e-93a5-4781-9d78-0ac9631cc22f" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bf37b70c-fc82-47a4-9ef9-6099e8519aa4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_bf37b70c-fc82-47a4-9ef9-6099e8519aa4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bf37b70c-fc82-47a4-9ef9-6099e8519aa4" xlink:to="loc_us-gaap_ReceivableTypeDomain_bf37b70c-fc82-47a4-9ef9-6099e8519aa4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_069d6e1f-efd7-44c5-ac9f-a8cda7293498" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bf37b70c-fc82-47a4-9ef9-6099e8519aa4" xlink:to="loc_us-gaap_ReceivableTypeDomain_069d6e1f-efd7-44c5-ac9f-a8cda7293498" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_EarnOutReceivableMember_3acca0a9-43a3-4e03-800d-944aa195a7b0" xlink:href="vsec-20250630.xsd#vsec_EarnOutReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_069d6e1f-efd7-44c5-ac9f-a8cda7293498" xlink:to="loc_vsec_EarnOutReceivableMember_3acca0a9-43a3-4e03-800d-944aa195a7b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_EarnOutReceivableRollForward_24503486-4e61-4eff-afe7-d0c2236705bc" xlink:href="vsec-20250630.xsd#vsec_EarnOutReceivableRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_949b8852-adb4-4777-a494-ac5f206bc8c1" xlink:to="loc_vsec_EarnOutReceivableRollForward_24503486-4e61-4eff-afe7-d0c2236705bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesFairValueDisclosure_d9bdd26e-d955-44ad-b0cd-4a6640091639" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivablesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_vsec_EarnOutReceivableRollForward_24503486-4e61-4eff-afe7-d0c2236705bc" xlink:to="loc_us-gaap_ReceivablesFairValueDisclosure_d9bdd26e-d955-44ad-b0cd-4a6640091639" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_ReceivablesFairValueEarnedDuringPeriod_97e3e813-3257-4257-b25f-c6fc5d4ee793" xlink:href="vsec-20250630.xsd#vsec_ReceivablesFairValueEarnedDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_vsec_EarnOutReceivableRollForward_24503486-4e61-4eff-afe7-d0c2236705bc" xlink:to="loc_vsec_ReceivablesFairValueEarnedDuringPeriod_97e3e813-3257-4257-b25f-c6fc5d4ee793" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_ReceivablesFairValueAdjustment_3824bd3a-83ca-40c0-a2fd-92527b203ae4" xlink:href="vsec-20250630.xsd#vsec_ReceivablesFairValueAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_vsec_EarnOutReceivableRollForward_24503486-4e61-4eff-afe7-d0c2236705bc" xlink:to="loc_vsec_ReceivablesFairValueAdjustment_3824bd3a-83ca-40c0-a2fd-92527b203ae4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesFairValueDisclosure_2839653e-8e51-43d8-af35-49688b36aefa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivablesFairValueDisclosure"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://vsecorp.com/role/LeaseAbandonmentandOtherRestructuringCostsNarrativeDetails" xlink:type="simple" xlink:href="vsec-20250630.xsd#LeaseAbandonmentandOtherRestructuringCostsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://vsecorp.com/role/LeaseAbandonmentandOtherRestructuringCostsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_d8ddad11-3d30-4190-8fcd-5d56f024d810" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d8ddad11-3d30-4190-8fcd-5d56f024d810" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_b6593933-401f-47c9-bc0a-e2fa0c179d20" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_b6593933-401f-47c9-bc0a-e2fa0c179d20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_b6593933-401f-47c9-bc0a-e2fa0c179d20_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_b6593933-401f-47c9-bc0a-e2fa0c179d20" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_b6593933-401f-47c9-bc0a-e2fa0c179d20_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_b6714c3a-4e8e-4291-9b00-321d63dca037" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_b6593933-401f-47c9-bc0a-e2fa0c179d20" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_b6714c3a-4e8e-4291-9b00-321d63dca037" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_c85a5b66-f5bc-4dc4-a519-ef43bd0eba11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_b6714c3a-4e8e-4291-9b00-321d63dca037" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_c85a5b66-f5bc-4dc4-a519-ef43bd0eba11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_19671447-2e4e-4e9a-a069-e0fd74008eff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_19671447-2e4e-4e9a-a069-e0fd74008eff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_19671447-2e4e-4e9a-a069-e0fd74008eff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_19671447-2e4e-4e9a-a069-e0fd74008eff" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_19671447-2e4e-4e9a-a069-e0fd74008eff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1380f4b-9106-4cc8-9345-b0713968e57a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_19671447-2e4e-4e9a-a069-e0fd74008eff" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1380f4b-9106-4cc8-9345-b0713968e57a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_FederalAndDefenseSegmentMember_69b31d89-2f58-4e66-9612-a5331fe76645" xlink:href="vsec-20250630.xsd#vsec_FederalAndDefenseSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_b1380f4b-9106-4cc8-9345-b0713968e57a" xlink:to="loc_vsec_FederalAndDefenseSegmentMember_69b31d89-2f58-4e66-9612-a5331fe76645" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_144c1bf1-1110-46aa-b599-e61764b8330e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_144c1bf1-1110-46aa-b599-e61764b8330e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_144c1bf1-1110-46aa-b599-e61764b8330e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_144c1bf1-1110-46aa-b599-e61764b8330e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_144c1bf1-1110-46aa-b599-e61764b8330e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_e3d527a1-6ddc-4662-99ec-cad18d98e923" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_144c1bf1-1110-46aa-b599-e61764b8330e" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_e3d527a1-6ddc-4662-99ec-cad18d98e923" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringMember_6c12a4f8-a503-4a60-8bfc-a74038a00db9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_e3d527a1-6ddc-4662-99ec-cad18d98e923" xlink:to="loc_us-gaap_OtherRestructuringMember_6c12a4f8-a503-4a60-8bfc-a74038a00db9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_a18a73ca-c8b2-40ae-a264-6686f96ae8c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5cccfe51-969f-4765-bf7b-56b9f0614731" xlink:to="loc_us-gaap_RestructuringPlanAxis_a18a73ca-c8b2-40ae-a264-6686f96ae8c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_a18a73ca-c8b2-40ae-a264-6686f96ae8c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_a18a73ca-c8b2-40ae-a264-6686f96ae8c2" xlink:to="loc_us-gaap_RestructuringPlanDomain_a18a73ca-c8b2-40ae-a264-6686f96ae8c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_b530166b-d047-4c21-80ca-63a0a961a49f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_a18a73ca-c8b2-40ae-a264-6686f96ae8c2" xlink:to="loc_us-gaap_RestructuringPlanDomain_b530166b-d047-4c21-80ca-63a0a961a49f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_vsec_LeaseAbandonmentMember_a2307ab3-0ace-46d9-b867-0f2526302075" xlink:href="vsec-20250630.xsd#vsec_LeaseAbandonmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_b530166b-d047-4c21-80ca-63a0a961a49f" xlink:to="loc_vsec_LeaseAbandonmentMember_a2307ab3-0ace-46d9-b867-0f2526302075" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnTerminationOfLease_34460b77-8be3-4841-96bd-23a39928ab56" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnTerminationOfLease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d8ddad11-3d30-4190-8fcd-5d56f024d810" xlink:to="loc_us-gaap_GainLossOnTerminationOfLease_34460b77-8be3-4841-96bd-23a39928ab56" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_e45c7942-421f-4775-9c9c-f2ea771bc477" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_d8ddad11-3d30-4190-8fcd-5d56f024d810" xlink:to="loc_us-gaap_RestructuringCharges_e45c7942-421f-4775-9c9c-f2ea771bc477" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
