Destroyers and Depth-Charging
The mid-war introduction of hedgehog helped in two ways. First, it threw the weapon ahead of the attacking ship, allowing the escort to remain in sonar contact right up to the point of firing (or nearly so), and second, the charge exploded on contact, not at a specific depth. So if you were attacking a target in deep water, any detonation could be assumed a "hit." And because hedgehog was a contact weapon, even a relatively small explosion right up against the hull was often enough to kill the sub outright.
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