Anti-submarine weapon
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An anti-submarine weapon is any one of a range of devices that are intended to act against a submarine, and its crew, to destroy (sink) the vessel or to destroy or reduce its capability as a weapon of war.
An anti-submarine weapon can be integrated with an anti-submarine warfare (ASW) Navy Tactical Data System (NTDS) that controls air, land and sea-based weapon system threat detection and target acquisition. However, in its simplest sense it is a projectile, missile or bomb that is optimized to destroy submarines.
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[edit] Development
[edit] World War I
World War I marked the first earnest conflict involving significant use of submarines and consequently marked the beginning of major efforts to counter that threat. In particular, the United Kingdom was desperate to defeat the German U-Boat threat against British merchant shipping. 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. During this period they found that setting the depth that the some charges exploded to be above, and below, the vessel was more efficient.
Before the war ended, the need for forward-throwing weapons had been recognized and trials began. Hydrophones had been developed and were becoming effective as detection devices. Also, aircraft and airships had flown with depth bombs (aerial depth charges), albeit quite small ones with poor explosives. In addition, the specialist hunter-killer submarine had appeared, HMS R-1.
[edit] World War II
[edit] Battle of the Atlantic
By the time of World War II, anti-submarine weapons had been developed somewhat, but during that war, there was a renewal of all-out submarine warfare by Germany as well as widespread use of submarines by most of the other combatants. The effective use of depth charges required the combined resources and skills of many individuals during an attack. Sonar information, helmsmen, depth charge crews and the movement of other ships had to be carefully coordinated in order to deliver a successful depth charge attack.
Air-dropped depth bombs were normally set to explode at a shallow depth, while the submarine was crash-diving to escape attack. As the Battle of the Atlantic wore on, British and Commonwealth forces in particular proved particularly adept at depth charge tactics, and formed some of the first destroyer hunter-killer groups to actively seek out and destroy German U-boats.
As a result, a host of new anti-submarine weapons were developed. Forward-throwing anti-submarine mortars were introduced in 1942. These mortars used small depth charges codenamed Hedgehog. One type created entire patterns of explosions underwater around a potential enemy, while the second type was fitted with contact detonators, meaning the warhead exploded only upon contact with the submarine. The latter design enabled a pursuing destroyer or destroyer escort to maintain continual sonar contact until a definite 'hit' was achieved. Additionally, new weapons were designed for use by aircraft, rapidly increasing their importance in fighting submarines. 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.
[edit] Pacific Theater
Japan, the United States, Great Britain, Holland, and Australia all employed anti-submarine forces in the Pacific Theater during World War II. Because the Japanese Navy tended to utilize its subs 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.
Early Japanese submarines were not very maneuverable under water, could not dive very deep, and lacked radar. Later in the war, Japanese submarines were fitted with radar scanning equipment. However, these radar-equipped subs were in some instances sunk due to the ability of U.S. radar receivers to detect their tell-tale scanning emissions. For example, Batfish (SS-310) sunk three Japanese radar-equipped submarines in the span of four days. 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.
In contrast, Allied submarines were largely committed against Japanese merchant shipping. As a consequence, Japanese anti-submarine forces were forced to spread their efforts to defend the entirety of their merchant shipping lanes, not only to resupply their forces, but also to continue the necessary importation of war material to the Japanese home islands.
At first, Japanese anti-submarine defenses proved less than effective against U.S. submarines. Japanese sub detection gear was not as advanced as that of some other nations. The primary Japanese anti-submarine weapon for most of WWII was the depth charge, and Japanese depth charge attacks by its surface forces initially proved fairly unsuccessful against U.S. fleet submarines. Unless caught in shallow water, a U.S. submarine commander could normally dive to a deeper depth in order to escape destruction, sometimes using temperature gradient barriers to escape pursuit. 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.
Unfortunately, the deficiencies of Japanese depth-charge tactics were revealed in a June 1943 press conference held by U.S. Congressman Andrew J. May, a member of the House Military Affairs Committee who had visited the Pacific theater and received many confidential intelligence and operational briefings. At the press conference, May revealed that American submarines had a high survivability because Japanese depth charges were fused to explode at too shallow a depth, typically 100 feet (because Japanese forces believed U.S. subs did not normally exceed this depth). Various press associations sent this story over their wires, and many newspapers, including one in Honolulu, thoughtlessly published it. Soon enemy depth charges were rearmed to explode at a more effective depth of 250 feet. Vice Admiral Charles A. Lockwood, commander of the U.S. submarine fleet in the Pacific, later estimated that May's revelation cost the navy as many as ten submarines and 800 crewmen.[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. Despite this onslaught, U.S. sub sinkings of Japanese shipping continued to increase at a furious rate as more U.S. subs deployed each month to the Pacific. By the end of the war, U.S. submarines had destroyed more Japanese shipping than all other weapons combined, including aircraft.
[edit] Post-war developments
The Cold War brought a new kind of conflict to submarine warfare. This war of development had both the United States and Soviet Union racing to develop better, stealthier and more potent submarines while consequently developing better and more accurate anti-submarine weapons and new delivery platforms, including the helicopter.
Attack submarines (SSKs and SSNs) were developed to include faster, longer range and more discriminating torpedoes. This, coupled with improvements to sonar systems, made ballistic missile submarines more vulnerable to attack submarines and also increased the anti-surface warfare (ASuW) capabilities of attack subs. 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.
To counter this increasing threat torpedoes were honed to target submarines more effectively and new anti-submarine missiles and rockets were developed to give ships a longer-range anti-submarine capability. Ships, submarines and Maritime Patrol Aircraft (MPA) also received increasingly effective technology for locating submarines, e.g. Magnetic Anomaly Detectors (MAD) and improved sonar.
[edit] Anti-Submarine Technology
Many concepts have been tried to come up with ways of attacking submarines. The first component of an Anti-submarine attack is detection: anti-sub weapons cannot be successfully employed without first locating the enemy submarine.
[edit] Detection Equipment
[edit] Radar
Radar was a prime tool in World War II for locating surfaced submarines. After the development of nuclear-powered subs became commonplace, submarines rarely surfaced outside their home port, rendering radar detection useless.
[edit] Sonar
Since World War II, sonar has emerged as the primary method of underwater detection of submarines. Its versatility has increased with the development of air-dropped sonar buoys, which relay sonar signals to overhead aircraft.
[edit] Magnetic Anomaly Detection
A Magnetic Anomaly Detector (MAD) is an electronic receiver designed to pick up the magnetic radiation of large metal objects, such as the steel hull of a submarine. Before the development of sonar buoys, MAD gear was often installed in aircraft to pick up shallow-submerged submarines. It is still used today.
[edit] Anti-submarine Weapons
[edit] Depth charge
The simplest of the anti-submarine weapons, the depth charge is a large canister filled with explosives and set to explode at a predetermined depth. The concussive effects of the explosion could damage a submarine from a distance, though a depth charge explosion had to be very close to break the submarine's hull. Air-dropped depth charges were referred to as 'depth bombs'; these were sometimes were fitted with an aerodynamic casing.
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. Depth charges improved considerably since their first employment in World War I. To match improvements in submarine design, pressure-sensing mechanisms and explosives were improved during World War II to provide greater shock power and a charge that would reliably explode over a wide range of depth settings.
Aerial-launched depth bombs are dropped in twos and threes in pre-computed patterns, either from airplanes, helicopters, or blimps. Since aerial attacks normally resulted from surprising the submarine on the surface, air-dropped depth bombs were usually timed to explode at a shallow depth, while the sub was in the process of making a crash dive. In many cases destruction was not achieved, but the submarine was nonetheless forced to retire for repairs.
Early depth charges were designed to be rolled into the water off of the stern of a fast ship. The ship had to be moving fast enough to avoid the concussion of the depth charge blast. Later designs allowed the depth charge to be hurled some distance from the ship, allowing slower ships to operate them and for larger areas to be covered.
Today, depth charges not only can be dropped by aircraft or surface ships, but can also be carried by missiles to their target.
[edit] Anti-submarine mortar
With the discovery that depth charges rarely scored a kill by hitting a submarine, but instead were most effective in barrages, it was found that similar or better effects could be obtained by larger numbers of smaller explosions. The anti-submarine mortar is actually an array of spigot mortars, designed to fire off a number of small explosives simultaneously and create an array of explosions around a submarine's position. These were often called Hedgehogs after the name given a World War II British design. 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.
[edit] Torpedo
The first successful homing torpedo was introduced by the German Navy for use by its U-boat arm against Allied shipping. After capturing several of these weapons, 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. FIDO was designed to breach the steel pressure hull of a submarine, but not necessarily cause a catastrophic implosion, enabling the now-crippled sub to surface where the sub and crew might possibly be captured. After World War II, homing torpedoes became one of the primary anti-submarine weapons, used by most of the world's naval powers. Aircraft continued to be the primary launching platform, including the newly available helicopter, though homing torpedoes can also be launched from surface ships or submarines. 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.
[edit] Mine
Similar to those designed to defeat surface ships, mines can be laid to wait for an enemy submarine to pass by and then explode to cause concussive damage to the submarine. Some are mobile and upon detection they can move towards the submarine until within lethal range. There has even been development of mines that have the ability to launch an encapsulated torpedo at a detected submarine. Mines can be laid by submarines, ships, or aircraft.
[edit] Anti-submarine Rocket
One of the latest anti-submarine weapons, Anti-Submarine ROCkets (ASROCs), SUBROC, the Ikara and the French Malafon missile differ from other types of missiles in that instead of having a warhead which the missiles delivers to the target directly and explodes, they carry another anti-submarine weapon to a point of the surface where that weapon is dropped in the water to complete the attack. The missile itself launches from its platform and travels to the designated delivery point.
The major advantages of a missile are range and speed of attack. Torpedoes are not very fast compared to a missile, nor as long-ranged, and are much easier for a submarine to detect. Anti-sub missiles are usually delivered from surface vessels, offering the surface escort an all-weather, all-sea-conditions instant readiness weapon to attack time-urgent targets that no other delivery system can match for speed of response. 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. Aircraft-delivery can be further compromised by low-fuel-state, or an expended weapon load. The missile is always available, and at instant readiness. It allows the torpedo or Nuclear Depth Bomb to enter the water practically on top of the submarine's position, minimizing the submarine's ability to detect and evade the attack. Missiles are also more rapid and accurate in many cases than helicopters or aircraft for dropping torpedoes and depth charges, with a typical interval of 1 to 1.5 minutes from a launch decision to torpedo splashdown. Helicopters frequently take much longer to just get off the escort's deck.
[edit] See also
- Anti-submarine warfare
- Autogyro
- Depth Charge
- Helicopter
- History of submarines
- Magnetic anomaly detector
- Radar
- Sonar
- Torpedo
[edit] References
- Blair, Clay, Silent Victory (Vol.1), The Naval Institute Press, 2001
- Lanning, Michael Lee (Lt. Col.), Senseless Secrets: The Failures of U.S. Military Intelligence from George Washington to the Present, Carol Publishing Group, 1995
