From what I've been able to pick up both on forums and books is that there was only One (1) actual Sinking of a U-boat by another U-boat (british) whilst both were submersed. (correct me If I'm wrong)
All others were by one submerged sinking the other whilst it was on the surface (happened on numerous occations around Indonesia/Singapore and at least once in the channel.
So in a sense the majority was a surface sinking not unlike what we have in the game (but obviously ship not U-boats).
Don't know about a Deck Gun fight. That would be interesting to see/hear about.
