Anti-submarine weapon

When the bombs that it employed were found to be ineffective it began equipping its destroyers with simple depth charges that could be dropped into the water around a suspected submarine's location.

The development of the FIDO (Mk 24 mine) anti-submarine homing torpedo in 1943 (which could be dropped from aircraft) was a significant contributor to the rising number of German sub sinkings.

Japan, the United States, Great Britain, The Netherlands, and Australia all employed anti-submarine forces in the Pacific Theater during World War II.

Because the Japanese Navy tended to utilize its submarines against capital ships such as cruisers, battleships and aircraft carriers, U.S. and Allied anti-submarine efforts concentrated their work in support of fleet defense.

Later in the war, Japanese submarines were fitted with radar scanning equipment for improved hunting while surfaced.

However, these radar-equipped submarines were in some instances sunk due to the ability of U.S. radar receivers to detect their tell-tale scanning emissions.

In 1944, U.S. anti-submarine forces began to employ the FIDO (Mk 24 mine) air-dropped homing torpedo against submerged Japanese subs with considerable success.

Additionally, during the first part of the war, the Japanese tended to set their depth charges too shallow, unaware that U.S. submarines possessed the ability to dive beyond 150 feet.

May, a member of the House Military Affairs Committee who had visited the Pacific theater and received many confidential intelligence and operational briefings.

[1][2] In addition to resetting their depth charges to deeper depths, Japanese anti-submarine forces also began employing autogyro aircraft and Magnetic Anomaly Detection (MAD) equipment to sink U.S. subs, particularly those plying major shipping channels or operating near the home islands.

By the end of the war, U.S. submarines had destroyed more Japanese shipping than all other weapons combined, including aircraft.

Attack submarines (SSKs and SSNs) were developed to include faster, longer range and more discriminating torpedoes.

SSBNs themselves as well as cruise-missile submarines (SSGNs) were fitted with increasingly more accurate and longer range missiles and received the greatest noise reduction technology.

The first component of an anti-submarine attack is detection: anti-sub weapons cannot be successfully employed without first locating the enemy submarine.

In World War II, high frequency direction finding (HF/DF or "Huff-duff) was used by Allied escort vessels to detect submarines making position or sighting reports.

Since World War II, sonar has emerged as the primary method of underwater detection of submarines.

The advantage with this type of weapon is that it requires a relatively small payload as it detonates in direct contact or within a very close proximity of the submarine.

This is to some degree compensated by a heavy payload, in some mines exceeding half a metric ton, but since the effect of an underwater explosion decreases with a factor of the distance cubed, an increase in payload of a depth charge from 100 to 200 kg would not result in more than a few meters in killing radius.

After the First World War, special ASW shells were developed for medium calibre naval guns.

Surface-launched depth charges are typically used in a barrage manner in order to cause significant damage through continually battering the submarine with concussive blasts.

Aerial-launched depth bombs are dropped in twos and threes in pre-computed patterns, either from airplanes, helicopters, or blimps.

Later ASW mortar shells were fitted with impact detonators that fired only after actual contact with the hull of the submarine, allowing sonar crews to maintain a constant sound track until a hit was achieved.

The first successful homing torpedo was introduced by Nazi Germany's Kriegsmarine for use by its U-boat arm against Allied shipping.

After capturing several of these weapons,[dubious – discuss] along with independent research, the United States introduced the FIDO air-dropped homing torpedo (also called the Mark 24 'mine' as a cover) in 1943.

However, the torpedo's inherent limitations in speed of attack and detection by the target have led to the development of missile-borne anti-submarine weapons that can be delivered practically on top of the enemy submarine, such as ASROC.

Aircraft delivery platforms have included both unmanned helicopters, such as the US DASH, and manned ones such as British Westland Wasp.

They have the added advantage that they are under the direct control of the escort vessel's commander, and unlike air-delivered weapons cannot be diverted to other taskings, or be dependent on weather or maintenance availability.

Later, mechanical computers were used to solve the fire control problem with electrical indication of weapon readiness.

Today the weapon firing process is carried out by digital computer with elaborate displays of all relevant parameters.

Passive countermeasures may consist of coatings to minimize a torpedo's sonar reflections or an outer hull to provide a stand-off from its explosion.