About deepwater torpedoes:
1). ALL Destroyers are immune to get hit by them.
2) Some Light cruisers are immune, too. However, should those ships make a hard turn they are likely to get hit (depends on how deep the torpedoes are on each tier).
3) Like the Black issues, very high damage deepwater torpedoes seem not to do as highest damage as they are supposed to do (After counting TDS).
My opinion: I would pick normal torpedoes over the deepwater ones because sometimes I can randomly hit a Destroyer or Cruiser in the way or when hiding in cap, & smokescreen. They should give the ships the option to change the torpedo type in battle instead of a seperated module.