you may want to do what i do when handling mod ships and subs,
Only attempt to use one at a time. Mod ships and subs tend to over write a lot of things and aren't generally compatible with each other.
One at a time and you might be able to find the sub you want in the list of available ships.
I install a ship, say the Kent class, or Skipjack, and play for a while then pull it out to play a regular boat or another mod.
Make sure that the mod boat you install is last in the order.
