[CaptainHaplo]

The other issue is that DC's make use of the fact that an explosion underwater is subject to specific physical properties. A surface (or near surface) explosion is under a highly different set of physics. The amount of explosive needed per charge to be effective would have been MUCH higher than that needed by a normal DC.

Also remember that a submarine hull is under vastly more amounts of stress per square inch than the hull of a floating ship. This also contributed greatly to the lethality of DC's - which again would change the equation when used against a surface ship.

If anything, I am suprised countermeasures such as tangle wires (for DD props were not used. Dive and as you do, release a semi-bouyant net to tangle the attackers props. You know he is going to be coming.... Put it into his path, immobilize him (or at least seriously harm his mobilty) - then turn the tables and blast him.