Limbo, or Anti Submarine Mortar Mark 10 (A/S Mk.10), was the final British development of a forward-throwing anti-submarine weapon originally designed during the Second World War. Limbo, a three-barreled mortar similar to the earlier Hedgehog and Squid which it superseded. It was developed by the Admiralty Underwater Weapons Establishment in the 1950s.
The system weighed 35 tons, including 51 projectiles, fired in 17 salvos. The firing distance of the mortars was controlled by opening gas vents; rounds could be fired from 400–1,000 yards (370–910 m).
The weapon was linked to the sonar system of the ship, firing on command when the target was in range. The rounds were projected so that they fell in a triangular pattern around the target. Limbo could fire in any direction around the ship and is reported[ to have been very accurate.
The firing was controlled by the Type 170 (and later the 502) attack sonar from the Sonar Control Room (SCR), which was generally located next to the operations room in the warship.
The 170 sonar had 3 operators who maintained sonar contact with the target and effectively aimed the weapon in bearing, range and depth. The operators were controlled by the SCO (Sonar Control Officer) who was in charge of the SCR.
When a contact had been confirmed as a hostile submarine, the SCO manually fired the Mortar from the SCR upon receiving the order from the captain in the operations room.
Limbo was also widely employed by the Royal Navy, the Royal Canadian Navy, and the Libyan Navy. The weapon was used by thre Royal Navy in the 1982 Falklands War, and remained in service in the Royal Navy and Commonwealth navies until the 1990s.