I know it will be a while before we see subs, but here is an idea onn how to add them to gameplay.
I think you could be able to take a sub like a U-boat. If subs ever do come into the game, maybe we can spread out the destroyers a little bit? The destroyers then automatically drop depth charges when a sub is within a certain range. A single depth charge wouldnt destroy a sub. But severely damage it and force it to surface, where the ack would eat it alive.
With depth charges being dropped it would encourage people to attack from stand-off positions OR head on. have a 2nd position for the deck cannon. Use F6 mode to aim torpedo (but only at parascope depth)