The Squid fired 6, 300-pound projectiles, which were set to explode in a pattern around the target at a predetermined depth. Essentially, forward fired depth charges. Hedgehog fired 24 projectiles with 30-pound charges and contact detonators. The hedgehog round was designed to punch a hole in the pressure hull on contact, but was essentially harmless unless it actually hit you. Hence, you fired off a lot of them at once. The Squid was designed to detonate a simultaneous pattern of 6 heavy charges around the u-boat and crush the hull in the process.

Both systems took advantage of what was originally a severe limitation of the escorts' Asdic -- you lost contact when you passed over the target, which was the point at which the target would make a radical course alteration, clap on full speed, and try to get out of the way. By firing the projectiles ahead, the target was still in your beam and it was possible to get greater accuracy and harder for him to manoeuvre out of the way.

J.T. McDaniel