you mean this one?
i found it the other day in the same AO and similar circumstances. It didn't engage the german surface group (which i also had lurking about), but i stumbled on it while patrolling, and managed to take a pic. It definitely looks like a british U-class, one of which was passed on to poland (although much later, around the end of 1940). I had assumed it was a british sub keeping an eye on things but it might represent some other earlier polish model in game. Or maybe it is indeed a british sub but was engaged by mistake by german ships in your game?