When viewing through the museum, it looks like the Turm7c_#_deck files are working. It was kind of hard to see for sure, so I started a new campaign in 1943 at Brest. The AI sub docked there, did have a working Turm file, as is shown in the screenshot. There is a timestamp iin the lower right. The conning tower, though, is still rusty. I went through the Turm DAT files like I said above and changed the conning tower tga to correspong to that of the DAT. Since the Turm tga's are working, but the conning tower isn't, could it be a hex edit issue?
