The German ship is signalling distress! Â Its flag is upside down. Â :-D
I was considering super battleships for Japan (and maybe USA) only. Â The plan was:
30 cost  5/5/2.  Takes 3 hits to sink.  A functional port can repair only 1 hit per turn.  No limit on how many you can build.  If limited only to Japan (Yamato class), super battleships cannot move through the Panama canal.
Never tried it though, we always end up playing by the book. Â
Edit: I think I may try some of your idea. The first hit is ‘free’ and the second applies damage. This means that even when going fresh into a battle while damaged it would take 2 hits to sink. A 30 ipc unit needs to be tough.