I have four SS4 crews permently collecting dust in my HQ, all around lvl85-92. I just got so bored of the playstyle I never play them anymore. Prefer BB-->CV-->AA-->ASW-->SS in this order myself. As a previous poster stated torp xp sucks. And that grind from SS4 to SS5 simply sucks too.
If there were enough ASW ships around and the XP was better it could be fun again, and challenging. As it is if there are no ASW or small ships, you simply sneak across the map, sink a couple of capital ships. Pop up for air while popping smoke to cover yourself and hopefully survive while your air builds back up. Dive under and sink yet more capital ships. Rinse and repeat until you are out of ammo.