I just tried it again without any other mod installed, and it certainly worked. But it puzzles me that no mods I had before made changes to sensible files
I will enable them one by one and see when the error happens. I think I have an idea of where it might lie: In the empty campaign files that allow quicker loading times. Probably since no other ships are loaded, some of the effects that the U-Boat shares with one of them also doesn't get loaded, and thus it will not show
