Game I have the conning tower textures are in the main \Textures folders, but the hull and all the assorted parts are in each sub's individual folders. With two variations, one for early war (black) the other for late war. Biggest trouble you'll have is texture mapping, trying to figure out what maps where, and if the model maker intended for the screws, cleats, hatches and diving planes to use the same texture it's impossible to repaint one without repainting them all.
Using the Salmon as an example, for early war I start with \Data\Submarine\NSS_Salmon\NSS_SalmonClass_T01.dds . Lower right corner is where all the kibbles & bits that are not part of the main hull are, so I paste a rainbow texture there;
In game that looks like this:
So the next step is to tinker with the rainbow mask overlay until I've located the actual mapping for the screws. If possible, it's not an easy task even if it is physically possible to isolate only the propellers and nothing else.