All the things I read says that the heavyweight (torptub sized) UUV do about 3-4 knots with about a 30-50 hour endurance, iirc. What they don't say is that ANY uuv currently in existence has ASW detection capability and are really only suitable to mine recon.
http://www.chinfo.navy.mil/navpalib/...logy/uuvmp.pdf
http://www.chinfo.navy.mil/navpalib/...e_15/wave.html
http://www.navyleague.org/sea_power/may06-14.php
Perhaps a very drastically reduced sensor capability with a 50+ nm range? That should make things interesting...