If you ever get out of port, I would think with a type XXI things should be relatively easier than with long obsolete VII's and IX's. I haven't taken a XXI for a test drive yet though but I'm looking forward to the opportunity when I work my way into 1944/1945.
I've read an account of one of the only real operational XXI's that was at sea after the surrender. I can't recall who commanded her, but he came across a British cruiser heavily escorted. He knew he couldn't attack but he wanted to see if he could make a mock attack to test the capabilities of the XXI.
He easily penetrated the screen and said he could have sunk the cruiser if he wanted to. All he could do was return to port with a glimpse of what might have been.