all you can really do is go as deep as possible and listen for the splashes... at the first hint that hedgehogs are in the water go ahead flank... maybe turn. a lot of it has to do with luck and avoiding detection in the first place.
hedgehogs sink quickly, and its difficult to manuever out of the way quickly enough to evade them, but i recall an occasion where i managed to evade about a dozen hedgehog runs before they finally got me so it is not impossible.
im not sure on the historical accuracy of launching a full scale assault on a convoy that late in the war.
single ships and targets of opportunity were the order of the day really... byt late 1943 convoy attacks were nearly impossible to survive.
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