The fixpak would help some things, but unfortunately not this issue fitzcarraldo. This the old reliable Stock game "deck gun issue"...
@ Zyhgar, if you do not have the "AdditionalRepository" listed, then you are most likely missing part of, if not the whole gun itself, as noted on page 4 of that pdf listed and linked above. That section states:
"... you need to actually have the weapon in the UpgradePackSlot on the boat. Search on “UserPlayerUnit 1.UpgradePackSlot 2”, which in FotRSU is the “ID=UpgAirSearchRadar” section. You most likely do NOT have an “[UserPlayerUnit 1.UpgradePackSlot 3]” section, which is the “ID=UpgDeckGun” section. The next section should be “[UserPlayerUnit 1.FunctionalSubsystem 1]”, and you will paste this section between the last line of the “[UserPlayerUnit 1.UpgradePackSlot 2]” section and the "[UserPlayerUnit 1.FunctionalSubsystem 1]” section:[UserPlayerUnit 1.UpgradePackSlot 3]
ID=UpgDeckGun
NameDisplayable=Deck Gun
Type=NULL
AcceptedTypes=USDeckGunBow,USDeckGunStern,USDeckGu nImpBow,USDeckGunImpSter
n,USDeckGunHvyBow,USDeckGunHvyStern,USDeckGunHvyDb l
UserCustomizable=Yes
IDLinkUpgradePackSlots=BowDeckGun,SternDeckGun
CurrentUpgradePack=4inch .50cal Stern Mount
IDLinkUpgradePackSlotsLoaded=NULL
Save the file, making certain that it remains named ActiveUserPlayerUnits.upc”, as a plain text file, and no extra data or file extensions added..."
Now, part of the problem with that, is the write-up was for a Balao boat, so the sectioning and gun names would be different for your boat. Your boat actually should have a Conning Tower upgrade before the AA gun upgrade, but we did make it to where if you had the first conning tower that it would still mount the gun properly. The game does not do these types of "upgrades" properly. Looking at the image of your submarine on the equipment and crewing page, your boat has the first conning tower. I think we can eliminate that issue with the next mod release - maybe... for the S-42 Class anyway.
The apparent main problem you have is that in the modded game, the S-18 and S-42 classes actually receive "down-graded" deck guns effective 1942-08-01, which happened in real life at various re-fits. The 4" guns then went to fleetboats. The missing gun positions usually happen on boats where the player has changed the "default" gun position. That is not possible with the S-18 and S-42 classes, since they can only mount forward guns, so I am at a loss on that, other than to postulate that maybe the conning tower / AA gun change (or lack thereof) may have influenced things?? Give me a bit here, and I'll do a Career Start at Brisbane with an S-42, and get you some good replacement text to fix the Save data. Reference that "NewColetrainsAndOthersDGfix.pdf" file in the Support / HowTo folder though, in the meantime, to familiarize yourself with the procedure involved. If you do not feel comfortable with the idea, you could always just zip up your "C:\Users \Username \Documents \SH4" folder, and I can do the surgery for you, send it back, and you put it back where it was. Just send me a PM if that's what you want. You could use any one of a number of web sites to post to, such as DropBox, MediaFire, Google Drive or MS OneDrive and the like...
