Read Beaches second one too, ' Dust on the Sea', it a better read than 'Run Silent, Run Deep.
As to running down life boats, I can't remember seeing or reading about that except in the fiction books but I do remember on the history channel on the color of war series a seaman on the Wahoo said that Mush Morton actually sunk a Troop Transport and than surfaced and machine gunned the survivors so they could not get ashore and get back into the war and kill Americans.

Harry

there is that question of them still being combatants or not if they are unarmed.