Anti-submarine mortars (also called "depth charge throwers" or "depth charge projectors" for most cases) are often larger versions of the
mortar used by
infantry and fire a projectile in relatively the same manner. They were created during
World War II as a development of the
depth charge and work on the same principle, many mortars initially using those changes as projectiles.
World War I , an anti-submarine mortar developed in 1917 Anti-submarine warfare did not become an issue of great concern until
World War I, when Germany used submarines in an attempt to strangle British shipping in the
Atlantic Ocean and elsewhere. The earliest way to counter a submarine was in the form of
depth charges, which were large canisters filled with explosives, rolled off the back of a ship and detonated by a
hydrostatic fuze. Depth charges served well throughout World War I but were not without flaws. A ship had to pass directly over a submarine to score an effective hit, and as such, depth charges were dropped in lines instead of more effective clusters and could only be carried in ships fast enough to avoid the concussion of the explosion. The depth charges were also not as effective as one might think at sinking a submarine: only a very close detonation would sink a submarine, and the problems of scoring a direct hit meant that a submarine was more often damaged than destroyed by depth charges. After World War I depth charge throwers were developed, which could hurl depth charges some from the side of a ship, perpendicular to its direction of travel. These were a significant improvement over the old method, permitting the use of large 'patterns' of up to ten depth charges from the throwers and
stern depth charge rails used together. However, they still required a ship to pass very close to a submarine, which entailed a loss of sonar (
ASDIC) contact during the final stages of the approach. Submarines could and did use this period to take evasive action. It was the British who developed the first anti-submarine mortars. Several versions appeared in 1917, most notably the
BL 7.5-inch naval howitzer. However, the anti-submarine mortar did not become a truly successful weapon until the advent of the multi-barrelled
Hedgehog 25 years later.
World War II During World War II, submarines once again posed a major threat to Allied shipping, which necessitated the development of more effective anti-submarine mortars. These all had the common characteristic of throwing multiple charges ahead of the attacking vessel while it was still in sonar contact with a submarine. The most successful was the
Hedgehog, which consisted of 24 small
spigot mortar rounds, each one in diameter and weighing with a warhead. Each projectile had a range of about and was fired in a circular pattern in front of a ship. While the warhead on a Hedgehog was much smaller than that of a depth charge, it scored three times as many kills than its predecessors. This was due to the use of a
contact fuze on the projectile, which would only detonate on impact with a target. Since the projectile would only explode on a hit, the long periods of
sonar "blackout" from the blast and turbulence of a conventional depth charge explosion were eliminated. In the later stages of World War II, the Hedgehog was complemented in British service by the
Squid three-barrelled depth charge mortar, which fired depth charges to a range of . ==List of weapons==