[Fincuan]

That seems correct to me, but did you edit the correct file? It must be My Documents\SH4\data\cfg\SaveGames\0000000X\ActiveUs erPlayerUnits.upc. I haven't yet tested if this works in 1.4, but it should judging by the files that the patch changed.

Here's what I did to get the Gato late war tower with twin 20mm AAs mounted. Make sure that you are at base and that any AA gunner slots are empty before doing this, or weird things might happen. Also backup the file you are going to edit:

1. Replace the everything between but not including [UserPlayerUnit 1.UnitPartSlot 1] and [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 1] with this:
   
   

   ID=GatoConningSlot
   NameDisplayable=Conning Tower Mount
   Type=NULL
   AcceptedTypes=GatoConningTower
   ExternalNodeName3D=Z01
   IDLinkUnitPartIntervalDefault1=19000101,19420531,GatoConningEarlyWar
   IDLinkUnitPartIntervalDefault2=19420601,19430331,GatoConningMedWar
   IDLinkUnitPartIntervalDefault3=19430401,19431231,GatoConningLateWar
   IDLinkUnitPartIntervalDefault4=19440101,19991231,GatoConningElite
   IDLinkUnitPartLoaded=GatoConningLateWar
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart]
   ID=GatoConningLateWar
   NameDisplayable=The bridge fairwater was completely cut down to reduce surfaced silhouette
   UnitPartInterval=1942-12-01, 1999-12-31
   Type=GatoConningTower
   ExternalLinkName3D=data/objects/Conning_Gato_03
   HullTextureNameOverride=data/Submarine/NSS_Gato/NSS_Gato_T02.tga
   HullLightmapTextureNameOverride=data/Submarine/NSS_Gato/NSS_Gato_O01.tga
   HullNormalmapTextureNameOverride=NULL
   MenuSilhouetteTextureNameOverride=Gato_Class_03.tga

2. Replace everything between but not including [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 2] and [UserPlayerUnit 1.UpgradePackSlot 1] with this:
   
   

   ID=GatoConn3AA
   CompartmentType=2
   FunctionalType=FlakRoom
   NameDisplayable=Back AA Gun
   Type=NULL
   MechanicalCoef=0.200000
   ElectricsCoef=0.000000
   GunsCoef=0.500000
   WatchmanCoef=0.500000
   WatchStandingCoef=0.048000
   MaintenanceCoef=0.014400
   RepairsCoef=0.072000
   ReloadingweaponCoef=0.072000
   SleepCoef=-0.120000
   LeadersSlots=0
   CrewMembersSlots=0
   EffciencyDenominator=1
   EffciencyDenominatorBS=1
   Hitpoints=200.000000
   CrewExposure=0.300000
   EquipmentsExposure=0.100000
   WeaponsExposure=0.100000
   ExternalDamageZoneTypeID3D=44
   StatusActive=No
   EfficiencyHumanFactor=1.000000
   EfficiencyMechanicFactor=1.000000
   Efficiency=0.907585
   Damage=0.000000
   DamageHitpointsConsumed=0.000000
   RemainingRepairTime=0000-00-00 00:00:00
   FltDamage=0.000000
   CriticalFlotation=0.300000
   FloodingLevel=0.000000
   FloodingTime=0000-00-00 00:00:00
   FloodingSpeed=0.016667
   DamageDescription1=NULL,0,0.2,0,1,1,Minor damage,0,0,NULL,0,0.2,0.471872
   DamageDescription2=NULL,0.2,0.6,0,1,1,Medium damage,0,0,NULL,0,0.2,0.324782
   DamageDescription3=NULL,0.6,1,0,1,1,Heavy damage,0,0,NULL,0,0.2,2.01716
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 2.WeaponSlot 1]
   ID=CTBackAA
   NameDisplayable=AA Mount
   Type=NULL
   AcceptedTypes=NULL
   UserCustomizable=No
   IDLinkBunker=GunsAmmoBunker
   ExternalNodeName3D=A01
   ExternalObjectName3D=NULL
   ExternalDamageZoneTypeID3D=-1
   IDLinkWeaponLoaded=20mmTwinUS, NULL
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 2.WeaponSlot 1.Weapon]
   ID=20mmTwinUS
   NameDisplayable=Twin 20mm AA Gun
   WeaponInterval=1941-12-01, 1942-12-01
   WeaponSlotType=NULL
   AmmoTypesAccepted=20mmAPUS
   AmmoTypeLoaded=NULL
   AmmoMagazineSize=120
   AmmoMagazineRemaining=0
   WeaponCrewMembersSlots=1
   ExternalLinkName3D=20mm_Twin_soclu
   FunctionalType=WpFlak
   Hitpoints=100.000000
   EfficiencyHumanFactor=0.907585
   EfficiencyMechanicFactor=1.000000
   Efficiency=0.907585
   Damage=0.000000
   DamageHitpointsConsumed=0.000000
   RemainingRepairTime=0000-00-00 00:00:00
   DamageDescription1=NULL,0,0.2,0,1,1,Jam,0,0,NULL,1,0.3,0.160572
   DamageDescription2=NULL,0,1,0,0.5,1,Chamber Explosion,50,5,NULL,1,2,13.6188
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 2.CrewMemberSlot 1]
   ID=CrewMemberSlot_FlakC1
   NameDisplayable=AA Gun Crew
   Type=Leader
   IDLinkCrewMemberLoaded=NULL
   WatchCrewMemberSlot3D=WM1@slot_A01
   BattleStationsCrewMemberSlot3D=WM1@slot_A01
   WatchAccessoriesForAdding3DObjects=NULL
   WatchAccessoriesForSubtracting3DObjects=NULL
   BattleAccessoriesForAdding3DObjects=NULL
   BattleAccessoriesForSubtracting3DObjects=NULL
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 3]
   ID=GatoConn3AA2
   CompartmentType=2
   FunctionalType=FlakRoom
   NameDisplayable=Fore AA Gun
   Type=NULL
   MechanicalCoef=0.200000
   ElectricsCoef=0.000000
   GunsCoef=0.500000
   WatchmanCoef=0.500000
   WatchStandingCoef=0.048000
   MaintenanceCoef=0.014400
   RepairsCoef=0.072000
   ReloadingweaponCoef=0.072000
   SleepCoef=-0.120000
   LeadersSlots=0
   CrewMembersSlots=0
   EffciencyDenominator=1
   EffciencyDenominatorBS=1
   Hitpoints=200.000000
   CrewExposure=0.300000
   EquipmentsExposure=0.100000
   WeaponsExposure=0.100000
   ExternalDamageZoneTypeID3D=44
   StatusActive=No
   EfficiencyHumanFactor=1.000000
   EfficiencyMechanicFactor=1.000000
   Efficiency=0.000000
   Damage=0.000000
   DamageHitpointsConsumed=0.000000
   RemainingRepairTime=0000-00-00 00:00:00
   FltDamage=0.000000
   CriticalFlotation=0.300000
   FloodingLevel=0.000000
   FloodingTime=0000-00-00 00:00:00
   FloodingSpeed=0.016667
   DamageDescription1=NULL,0,0.2,0,1,1,Minor damage,0,0,NULL,0,0.2,0.390936
   DamageDescription2=NULL,0.2,0.6,0,1,1,Medium damage,0,0,NULL,0,0.2,0.427602
   DamageDescription3=NULL,0.6,1,0,1,1,Heavy damage,0,0,NULL,0,0.2,1.97566
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 3.WeaponSlot 1]
   ID=CTForeAA
   NameDisplayable=Fore AA Mount
   Type=NULL
   AcceptedTypes=NULL
   UserCustomizable=No
   IDLinkBunker=GunsAmmoBunker
   ExternalNodeName3D=A02
   ExternalObjectName3D=NULL
   ExternalDamageZoneTypeID3D=-1
   IDLinkWeaponLoaded=20mmTwinUS, NULL
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 3.WeaponSlot 1.Weapon]
   ID=20mmTwinUS
   NameDisplayable=Twin 20mm AA Gun
   WeaponInterval=1941-12-01, 1942-12-01
   WeaponSlotType=NULL
   AmmoTypesAccepted=20mmAPUS
   AmmoTypeLoaded=NULL
   AmmoMagazineSize=120
   AmmoMagazineRemaining=0
   WeaponCrewMembersSlots=1
   ExternalLinkName3D=20mm_Twin_soclu
   FunctionalType=WpFlak
   Hitpoints=100.000000
   EfficiencyHumanFactor=0.000000
   EfficiencyMechanicFactor=1.000000
   Efficiency=0.000000
   Damage=0.000000
   DamageHitpointsConsumed=0.000000
   RemainingRepairTime=0000-00-00 00:00:00
   DamageDescription1=NULL,0,0.2,0,1,1,Jam,0,0,NULL,1,0.3,0.180235
   DamageDescription2=NULL,0,1,0,0.5,1,Chamber Explosion,50,5,NULL,1,2,12.9945
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.Compartment 3.CrewMemberSlot 1]
   ID=CrewMemberSlot_FlakC2
   NameDisplayable=AA Gun Crew
   Type=Leader
   IDLinkCrewMemberLoaded=NULL
   WatchCrewMemberSlot3D=WM1@slot_A02
   BattleStationsCrewMemberSlot3D=WM1@slot_A02
   WatchAccessoriesForAdding3DObjects=NULL
   WatchAccessoriesForSubtracting3DObjects=NULL
   BattleAccessoriesForAdding3DObjects=NULL
   BattleAccessoriesForSubtracting3DObjects=NULL
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.UpgradePackSlot 1]
   ID=UpgAAGun
   NameDisplayable=Aft Anti-Aircraft Gun
   Type=NULL
   AcceptedTypes=USLightAA,USHeavyAA
   UserCustomizable=Yes
   IDLinkUpgradePackSlots=CTBackAA
   CurrentUpgradePack=Upack20mmTwin
   IDLinkUpgradePackSlotsLoaded=NULL
   
   [UserPlayerUnit 1.UnitPartSlot 1.UnitPart.UpgradePackSlot 2]
   ID=UpgBowAAGun
   NameDisplayable=Fore Anti-Aircraft Gun
   Type=NULL
   AcceptedTypes=USLightAA,USHeavyAA
   UserCustomizable=Yes
   IDLinkUpgradePackSlots=CTForeAA
   CurrentUpgradePack=Upack20mmTwin
   IDLinkUpgradePackSlotsLoaded=NULL

There's one possible problem with that: GatoConningLateWar has two crew slots for each AA compartment, while the above edit adds only one. Everything up to and including the Twin 20mm works fine, since they only need one crew member per gun to operate. The 40 mm, however, needs two crew members, and thus might require manually adding the second slot for each AA compartment. At the moment I just don't know what really happens with the 40 mm after the above edit.