Greetings,
Since Ubisoft will deprive me from enjoyning cute colored cutaway artworks at the damage screens, like in SHIII, SHI and even SHII, I have to go around the internet finding my own. Thought it would be nice to share my findings.
Gato:

No compartment descriptions.
http://www.mackinnon.org/gato-diagram-info.jpg
Descriptions covering the artwork, doh!
Balao:

No descriptions either. But the conning tower and deck gun are the only differences.
"A modern sub":
http://www.maritime.org/fleetsub/app...es/figa-01.htm
Hehe. No idea what this is. That's what it says. But it has all the descriptions! From this book:
http://www.maritime.org/fleetsub/chap3.htm#3A
Click "Next Appendix", lots of cutaways, some highlighting different components.
Oh well, that's all.