If you know what direction the escorts would come from then I would position one under the stack and one in good spot for that ship. Then move out to 3000 yrds or more and deck gun any ship that you torpedoed but did not sink plus any other ship you can get unitl your reload is done, the attack again with torpedoes.
Do this until out of ammo. If the escorts show up run away on the surface in the opposite direction. If planes show up you will probably need to run away on the surface and fight them until you have at least 100 feet of water so you can get to at least 80 feet.
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