I believe that you will see holes and stuff even in your own sub if it gets damaged. I've seen a screenshot of it in the screenshot thread (too busy to dig it up now). However, if the game models bent metal I dunno. I do doubt it though. So probably just sheer holes if you get hit with nasty stuff

But the damage model itself (that is, not the graphical, but data stuff) is really good. Already in SH3 it was decent, so I doubt it's any worse in SHIV.