What was hedgehog in the World War 2?

Answer 1

The Hedgehog was a forwardly fired device from ships involved in anti submarine warfare. A group of devices would be fired forward of the attacking ship where they believed the submarine to be. The devices were contact detonated so the sonar man aboard the attacking vessel could still hear the submarine unless the device struck its target unlike depth charges which could sometime put so much noise in the water from the explosions that it would take up to 15 minutes for the sonar man to get a clear listening to the area.. They were fired from a device which allowed the hedgehogs to enter the water in a circular pattern for a more effective range and area to strike the submerged vessel.

They were first created by the British and by the end of the war were also used heavily in the Pacific theater by the U.S. Allied forces against Japanese submarines.