[propbeanie]

I am not an expert at it, by any stretch, but check your Mission Parameter settings, versus the dates that the submarines are available in the game's "time frame". In other words, you might have a submarine selected that wasn't "in theatre" until March of 1943, but your mission is set to February 1943. Also, you can't have your player sub too close to ships or groups that "spawn", and I forget the exact distance required. If you open one of the other sub school missions, and take a peek at what they did (which is a LOT), you can get some good examples.

I do not know, and have not tried to find out how they do the boat selection thingie. That would be nice to do for some regular Single Missions also, where you might not feel like working so hard in an S boat, and would like a Gar, or at least ~something~ with a stern tube... |;^) - I'll see if I can figure that out, else maybe someone else will come along in a bit.