If you are willing to work for your renown then RealUBoat is an absolute must.
You may get bored of searching for ships aka surface for a couple of hours, dive, make a hydrophone sweep, surface for a couple of hours, dive....etc etc. But when you do hear a ship and charge in the general direction, make visual contact, and then sink the bugger....well all that furstration pays off....you get a real sense of achievement.
And once you've patrolled your grid square, why not linger around the main shipping routes north and south of Ireland. There is no better feeling than hearing a ship, making visual contact onluy to hear:
"Ship Spotted....bearing 278, Long range"
"Ship Spotted....bearing 275, Long range"
"Ship Spotted....bearing 284, Long range"
........
A convoy, a bloody big convoy!!!
Enjoy