Chinese u-47's WSM (War Ship Mod). There are quite a few of us taking destroyers, cruisers, aircraft carriers and even the mighty Bismarck out between our u-boat patrols.
Details are at:
http://www.subsim.com/radioroom//sho...d.php?t=157060
Great fun for a while, but the cat and mouse of u-boats has more appeal to me than the brute force approach of driving the Bismarck into a huge convoy and tearing it to shreds.