I think the Kapitanleutnant is the highest rank in the game. There is a way to change it, check
this thread.
The medals are related to your renown. Either sink more ships
, or increase your realism percentage (it effects renown).
I wouldn't know about stabilizing the XXI at PD. I'm playing with one at the moment (GWX) and it seems stable. Maybe it's a stock game issue?
Welcome aboard!
