Depth Charge, explosive charge, or bomb, designed to go off under water at a given depth by means of a hydrostatic detonator and used as a weapon against submarines. A direct hit is not always necessary with a depth charge because the concussion of its explosion is effective at some distance under water. Depth charges first came into use during World War I. The early forms of the weapon consisted of large cylinders containing TNT, which were rolled or catapulted, usually two at a time, from the stern of a ship. During World War II depth charges and machinery for launching them were improved. The use of a new and more powerful explosive called Torpex, a mixture of RDX, TNT, and aluminium, materially reduced the size of depth charges. The casings were also streamlined to make the charges sink faster.

The more recent depth charges carry magnetic or acoustic devices that detonate the explosives in the vicinity of enemy craft. Two types of multiple-launching mortars were also developed. One, nicknamed Hedgehog, threw charges in a circular pattern far ahead of the ship that launched it, and a lighter launcher with less recoil, nicknamed Mousetrap, threw a pattern of charges in a straight line ahead of the launching vessel and at right angles to its path. Today, depth charges are being replaced by antisubmarine rockets (ASROC). The ASROC is a rocket-thrown torpedo that, upon impact with the water, searches for the submarine. See also naval vessels.