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<?xml version="1.0" encoding="windows-1252"?> |
<ownershipDocument> |
| <schemaVersion> X0306 </schemaVersion> |
| <documentType> 4 </documentType> |
| <periodOfReport> 2021-03-05 </periodOfReport> |
| <issuer> |
| | <issuerCik> 0001411207 </issuerCik> |
| | <issuerName> Allison Transmission Holdings Inc </issuerName> |
| | <issuerTradingSymbol> ALSN </issuerTradingSymbol> |
| | </issuer> |
| <reportingOwner> |
| | <reportingOwnerId> |
| | | <rptOwnerCik> 0001543507 </rptOwnerCik> |
| | | <rptOwnerName> Scroggins Eric C. </rptOwnerName> |
| | | </reportingOwnerId> |
| | <reportingOwnerAddress> |
| | | <rptOwnerStreet1> ONE ALLISON WAY </rptOwnerStreet1> |
| | | <rptOwnerStreet2></rptOwnerStreet2> |
| | | <rptOwnerCity> INDIANAPOLIS </rptOwnerCity> |
| | | <rptOwnerState> IN </rptOwnerState> |
| | | <rptOwnerZipCode> 46222 </rptOwnerZipCode> |
| | | <rptOwnerStateDescription></rptOwnerStateDescription> |
| | | </reportingOwnerAddress> |
| | <reportingOwnerRelationship> |
| | | <isDirector> 0 </isDirector> |
| | | <isOfficer> 1 </isOfficer> |
| | | <isTenPercentOwner> 0 </isTenPercentOwner> |
| | | <isOther> 0 </isOther> |
| | | <officerTitle> VP, Gen. Counsel and Secretary </officerTitle> |
| | | <otherText></otherText> |
| | | </reportingOwnerRelationship> |
| | </reportingOwner> |
| <nonDerivativeTable></nonDerivativeTable> |
| <derivativeTable> |
| | <derivativeTransaction> |
| | | <securityTitle> |
| <value> Dividend Equivalent Rights </value> |
| </securityTitle> |
| | | <conversionOrExercisePrice> |
| <footnoteId id="F1"/> |
| </conversionOrExercisePrice> |
| | | <transactionDate> |
| <value> 2021-03-05 </value> |
| </transactionDate> |
| | | <transactionCoding> |
| <transactionFormType> 4 </transactionFormType> |
| <transactionCode> A </transactionCode> |
| <equitySwapInvolved> 0 </equitySwapInvolved> |
| </transactionCoding> |
| | | <transactionAmounts> |
| <transactionShares> |
| <value> 30 </value> |
| </transactionShares> |
| <transactionPricePerShare> |
| <value> 0 </value> |
| </transactionPricePerShare> |
| <transactionAcquiredDisposedCode> |
| <value> A </value> |
| </transactionAcquiredDisposedCode> |
| </transactionAmounts> |
| | | <exerciseDate> |
| <footnoteId id="F1"/> |
| </exerciseDate> |
| | | <expirationDate> |
| <footnoteId id="F1"/> |
| </expirationDate> |
| | | <underlyingSecurity> |
| <underlyingSecurityTitle> |
| <value> Common Stock </value> |
| </underlyingSecurityTitle> |
| <underlyingSecurityShares> |
| <value> 30 </value> |
| </underlyingSecurityShares> |
| </underlyingSecurity> |
| | | <postTransactionAmounts> |
| <sharesOwnedFollowingTransaction> |
| <value> 128 </value> |
| </sharesOwnedFollowingTransaction> |
| </postTransactionAmounts> |
| | | <ownershipNature> |
| <directOrIndirectOwnership> |
| <value> D </value> |
| </directOrIndirectOwnership> |
| </ownershipNature> |
| | | </derivativeTransaction> |
| | </derivativeTable> |
| <footnotes> |
| | <footnote id="F1"> The dividend equivalent rights accrued on previously awarded restricted stock units ("RSUs") and vest proportionately with the RSUs to which they relate. Each dividend equivalent right is the economic equivalent of one share of Allison Transmission Holdings, Inc. common stock. </footnote> |
| | </footnotes> |
| <remarks></remarks> |
| <ownerSignature> |
| | <signatureName> /s/ Jacalyn C. Bolles, attorney-in-fact </signatureName> |
| | <signatureDate> 2021-03-09 </signatureDate> |
| | </ownerSignature> |
| </ownershipDocument> |