depth charge, explosive device used against submarines and other underwater targets, either rolled into the water from rails on the stern of a ship or propelled from depth charge throwers. The charge is detonated by water pressure at a predetermined depth. It does not have to come into actual contact with the target to destroy it, since the concussion can accomplish this if the charge explodes near enough. First used by the British navy in World War I, it contributed significantly to the defeat of the German U-boat campaign.