[propbeanie]

Like I said, if you have let's say v1.24 of FotRSU, and you install vickers03's interior mod, it overwrites the SubName.upc of the submarine. Your first assignments after the first start might be fine with the deck gun, but not always. And as soon as you "upgrade" the boat, the game cannot find the deck gun, because the configuration of a file in UPCData / UPCUnitsData does not match the SubName.upc file, hence, the game will do what you encountered. It really should tell you up front "Hey! Something is wrong here!" and not go, but ~no~, they've gotta let you go out on patrol and sink ships, complete objectives, and really contribute to the war effort, only to disappoint you next time you go to load the Save, because the configurations don't match... No true "fail-safe" in the game's code, nor any error trapping the consumer can get at... other than the CTD... sigh.

However, if you install the patch for vickers' interiors, then it matches the SubName.upc to the other info in UPCData / UPCUnitsDat... If you have v1.24, there will be that "910_" mod in the Extras folder. Otherwise, download vickers' update, linked to above. You should delete the Save folder data (by Windows default, "C:\Users \UserName \Documents \SH4"), just like you would for a new install, so that the bad data is cleared, and the new, matching data is then pulled in. Else you'll still have the old UPC files in the Save folder data... You might be able to use a previous Save game, prior to any upgraded boat, and refuse the new boat when you come back in, Save, Exit, and apply the interior patch, then go back out patrolling and see what happens, but don't count on success with that. It could be a waste of time trying to recover.