# Anti-submarine weapon

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An anti-submarine weapon (ASW) is any one of a number of devices that are intended to act against a submarine and its crew, to destroy (sink) the vessel or reduce its capability as a weapon of war. In its simplest sense, an anti-submarine weapon is usually a projectile, missile or bomb that is optimized to destroy submarines.

A projectile is any object thrown into space by the exertion of a force. Although any object in motion through space may be called a projectile, the term more commonly refers to a ranged weapon. Mathematical equations of motion are used to analyze projectile trajectory. An object projected at an angle to the horizontal has both the vertical and horizontal components of velocity. The vertical component of the velocity on the y-axis given as Vy=USin(teta) while the horizontal component of the velocity Vx=UCos(teta). There are various terms used in projectiles at specific angle teta 1. Time to reach maximum height. It is symbolized as (t), which is the time taken for the projectile to reach the maximum height from the plane of projection. Mathematically, it is give as t=USin(teta)/g Where g=acceleration due to gravity(app 10m/s²) U= initial velocity (m/s) teta= angle made by the projectile with the horizontal axis.

In modern language, a missile, also known as a guided missile, is a guided self-propelled system, as opposed to an unguided self-propelled munition, referred to as a rocket. Missiles have four system components: targeting or missile guidance, flight system, engine, and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles, surface-to-air missiles, air-to-air missiles, and anti-satellite weapons. All known existing missiles are designed to be propelled during powered flight by chemical reactions inside a rocket engine, jet engine, or other type of engine. Non-self-propelled airborne explosive devices are generally referred to as shells and usually have a shorter range than missiles.

A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, and explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia.

## History

### Before World War I

Prior to about 1890, naval weapons were only used against surface shipping. With the rise of the military submarine after this time, countermeasures were considered for use against them. The first submarine installation of torpedo tubes was in 1885 and the first ship was sunk by a submarine-launched torpedo in 1887. There were only two ways of countering the military submarine initially: ramming them or sinking them with gunfire. However, once they were submerged, they were largely immune until they had to surface again. By the start of the First World War there were nearly 300 submarines in service with another 80 in production.

A submarine is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term most commonly refers to a large, crewed vessel. It is also sometimes used historically or colloquially to refer to remotely operated vehicles and robots, as well as medium-sized or smaller vessels, such as the midget submarine and the wet sub. The noun submarine evolved as a shortened form of submarine boat; by naval tradition, submarines are usually referred to as "boats" rather than as "ships", regardless of their size.

### 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 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 it was found that explosions of these charges were more efficient if the charges were set to explode below or above the submarine. However, many other techniques were used, including minefields, barrages and Q-ships and the use of cryptanalysis against intercepted radio messages. The airship ("blimp") was used to drop bombs but fixed-wing aircraft were mostly used for reconnaissance. However, the most effective countermeasure was the convoy. In 1918 U-boat losses became unbearably high. During the war a total of 178 U-boats were sunk, by the following causes:

World War I, also known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history. It is also one of the deadliest conflicts in history, with an estimated nine million combatants and seven million civilian deaths as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide.

The United Kingdom, officially the United Kingdom of Great Britain and Northern Ireland but more commonly known as the UK or Britain, is a sovereign country lying off the north-western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state‍—‌the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland. With an area of 242,500 square kilometres (93,600 sq mi), the United Kingdom is the 78th-largest sovereign state in the world. It is also the 22nd-most populous country, with an estimated 66.0 million inhabitants in 2017.

In naval terminology, a destroyer is a fast, maneuverable long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller powerful short-range attackers. They were originally developed in the late 19th century by Fernando Villaamil for the Spanish Navy as a defense against torpedo boats, and by the time of the Russo-Japanese War in 1904, these "torpedo boat destroyers" (TBDs) were "large, swift, and powerfully armed torpedo boats designed to destroy other torpedo boats". Although the term "destroyer" had been used interchangeably with "TBD" and "torpedo boat destroyer" by navies since 1892, the term "torpedo boat destroyer" had been generally shortened to simply "destroyer" by nearly all navies by the First World War.

• Mines: 58;
• Depth charges: 30;
• Gunfire: 20;
• Submarine torpedoes: 20;
• Ramming: 19;
• Unknown: 19;
• Accidents: 7;
• Other (including bombs): 2

British submarines operated in the Baltic, North Sea and Atlantic as well as the Mediterranean and Black Sea. Most of the losses were due to mines but two were torpedoed. French, Italian and Russian submarines were also destroyed.

Before the war ended, the need for forward-throwing weapons had been recognized by the British and trials began. Hydrophones had been developed and were becoming effective as detection and location 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.

A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a sound wave. Some piezoelectric transducers can also serve as a sound projector, but not all have this capability, and some may be destroyed if used in such a manner.

### Inter-war

The main developments in this period were in detection, with both active sonar (ASDIC) and radar becoming effective. The British integrated the sonar with fire control and weapons to form an integrated system for warships. Germany was banned from having a submarine fleet but began construction in secret during the 1930s. When war broke out it had 21 submarines at sea.

Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object(s). Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.

In the inter-war period Britain and France had experimented with several novel types of submarine. New sonars and weapons were developed for them.

### World War II

#### Atlantic/Mediterranean Theatre

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. 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.

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

Germany, officially the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north, and the Alps to the south. It borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, France to the southwest, and Luxembourg, Belgium and the Netherlands to the west.

The Battle of the Atlantic was the longest continuous military campaign in World War II, running from 1939 to the defeat of Germany in 1945, and was a major part of the Naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. It was at its height from mid-1940 through to the end of 1943.

Air-dropped depth bombs were normally set to explode at a shallow depth, while the submarine was crash-diving to escape attack. Aircraft were very successful in not only attacking U-boats, but also in disrupting U-boats from carrying out attacks against ships. Some were fitted with a searchlight as well as bombs.

A host of new anti-submarine weapons were developed. Forward-throwing anti-submarine mortars were introduced in 1942 to prevent loss of sonar contact. These mortars, the first being Hedgehog, fired a pattern of small depth charges. One type of charge was used to create entire patterns of explosions underwater around a potential enemy, while the second type of round was fitted with contact detonators, meaning the warhead exploded only upon contact with the submarine. A later 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.

#### Pacific Theater

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.

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 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. For example, Batfish sank 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.

### 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.

## Anti-submarine technology

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

### Detection equipment

#### Optical detection

Initial methods involved making visual contact with the submarine, and remains an important method of target confirmation. This may now be supplemented by thermal techniques. However, the low "indiscretion rate" of modern submarines means that optical detection is now less successful.

The use of the "wolf pack" by submarines in both the first and second World Wars allowed interception of radio signals. Though these were encrypted, they were broken by the British at "Room 40" in the First World War and by Bletchley Park during the second. This allowed convoys to be diverted and hunter-killer groups to be targeted on the pack. Submarines now transmit using methods that are less susceptible to intercept.

Radar was a prime tool in World War II for locating surfaced submarines. After development of the snorkel, and then of nuclear-powered submarines, submarines rarely surfaced outside their home port, rendering direct radar detection largely useless. However, it is possible that radar can detect the surface effects produced by a submarine.

#### Sonar

Since World War II, sonar has emerged as the primary method of underwater detection of submarines. The most effective type has varied between active and passive, depending on the countermeasures taken by the submarine. Its versatility has increased with the development of air-dropped sonobuoys, which relay sonar signals to overhead aircraft, dipping sonar from helicopters and fixed long range systems.

#### Magnetic anomaly detection

A magnetic anomaly detector (MAD) is an electronic magnetometer designed to measure magnetic field variations caused by 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.

#### Other non-acoustic methods

Submarine detector loops were one of the first ways of finding the presence of an underwater submarine. The "sniffer" for detecting diesel exhausts was developed in the Second World War. More recently indirect methods of submarine detection have been tried, mainly via its wake.

### Anti-submarine weapons

Anti-submarine weapons can be divided into three categories according to their mode of operation: guided weapons, non-guided weapons and rocket and mortar weapons.

Guided anti-submarine weapons, such as torpedoes, seek out the submarine, either via its own sensors or from the launching platform's sensors. The advantage with this type of weapon is that it requires a relatively small payload since it detonates in direct contact or within a very close proximity of the submarine. The disadvantage is that this type of weapon can be decoyed and is adversely affected by stealth features of the submarine.

Non-guided anti-submarine weapons, such as mines and depth charges, are "dumb" weapons that has to be carried to the submarine or that the submarine has to come in close proximity of. 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.

Rockets' and mortar weapons', such as anti-submarine grenades and anti-submarine rockets, main advantage is the rapid response time since they are carried through the air to the target. Once dropped on top of the target, they also have the advantage of not being sensitive to decoys or stealth features. A hybrid of this category is the rocket launched torpedo, which is carried to the proximity of the target via a rocket and therefore reduces the response time and gives the submarine less time to undertake countermeasures or evasive maneuvers.

Finally, a submarine can of course also be destroyed by means of artillery fire and missiles in the rare case that a modern submarine surfaces, but these weapons are not specifically designed for submarines and their importance in modern anti-submarine warfare is very limited.

#### Guns/missiles

Gunfire has been used to disable submarines from the First World War onwards, while a helicopter missile attack was used to disable the Santa Fé in the Falklands War. After the First World War, special ASW shells were developed for medium calibre naval guns.

#### Depth charge

Perhaps 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 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 submarine 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.

#### 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 to 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.

The Hedgehog fired twenty-four 14.5 kg charges whereas a later development called the "Squid" fired three full-sized depth charges. A further development called "Limbo" was used into the 1960s, and this used 94 kg charges.

A development of the anti-submarine mortar, designed primarily for the exceptionally challenging task of littoral anti-submarine operations, utilizes a shaped charge warhead. An example of this is the Saab Dynamics Elma ASW-600 and the upgraded ASW-601 on YouTube.

#### Torpedo

The early anti-submarine torpedoes were straight-running types and usually a group was fired in case the target manoeuvred. They can be divided into two main types, the heavyweight, fired from submarines, and the lightweight which are fired from ships, dropped from aircraft (both fixed wing and helicopters) and delivered by rocket. Later ones used active/passive sonar homing and wire-guidance. Pattern running and wake homing torpedoes have also been developed.

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, 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, forcing the now-crippled submarine to surface where the submarine 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 a 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.

On ships the torpedoes are generally launched from a triple-barreled launcher by compressed air. These may be mounted on deck or below. On submarines torpedoes have been carried externally as well as internally. The latter have been launched in the past by stern tubes as well as by the more normal forward ones.

Aircraft delivery platforms have included both unmanned helicopters, such as the US DASH, and manned ones such as British Westland Wasp. The helicopter may be solely a weapons carrier or it can have submarine detection capabilities.

#### Mine

Similar to naval mines 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.

#### Anti-submarine rockets and missiles

One of the latest anti-submarine weapons, Anti-Submarine ROCkets (ASROCs), SUBROC, the Ikara, the French Malafon, and the Italian MILAS 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 anti-submarine missiles 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.

### Weapon control systems

The readiness of weapons was at first determined manually. Early fire control consisted of range measurements and calculation of the submarines course and speed. The aiming point was then manually determined by rule. 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.

## ASW Countermeasures

The main countermeasure the submarine has is stealth; it tries not to be detected. Against the ASW weapon itself, both active and passive countermeasures are used. The former may be a noise making jammer or a decoy providing a signal that looks like a submarine. 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. The anti-submarine weapon has to overcome these countermeasures.

## Related Research Articles

The RUR-5 ASROC is an all-weather, all sea-conditions anti-submarine missile system. Developed by the United States Navy in the 1950s, it was deployed in the 1960s, updated in the 1990s, and eventually installed on over 200 USN surface ships, specifically cruisers, destroyers, and frigates. The ASROC has been deployed on scores of warships of many other navies, including Canada, Germany, Italy, Japan, the Republic of China, Greece, Pakistan and others.

A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, any vessel. Naval mines can be used offensively, to hamper enemy shipping movements or lock vessels into a harbour; or defensively, to protect friendly vessels and create "safe" zones.

Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

A depth charge is an anti-submarine warfare weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive hydraulic shock. Most depth charges use high explosive charges and a fuze set to detonate the charge, typically at a specific depth. Depth charges can be dropped by ships, patrol aircraft, and helicopters.

The USS Tunny (SS/SSG/APSS/LPSS-282) was a Gato-class submarine which saw service in World War II and in the Vietnam War. Tunny received nine battle stars and two Presidential Unit Citations for her World War II service and five battle stars for her operations during the Vietnam War.

The Hedgehog was a forward-throwing anti-submarine weapon that was used during the Battle of the Atlantic in the Second World War. The device, which was developed by the Royal Navy, fired up to 24 spigot mortars ahead of a ship when attacking a U-boat. It was deployed on convoy escort warships such as destroyers and corvettes to supplement the depth charges.

An electronic countermeasure (ECM) is an electrical or electronic device designed to trick or deceive radar, sonar or other detection systems, like infrared (IR) or lasers. It may be used both offensively and defensively to deny targeting information to an enemy. The system may make many separate targets appear to the enemy, or make the real target appear to disappear or move about randomly. It is used effectively to protect aircraft from guided missiles. Most air forces use ECM to protect their aircraft from attack. It has also been deployed by military ships and recently on some advanced tanks to fool laser/IR guided missiles. It is frequently coupled with stealth advances so that the ECM systems have an easier job. Offensive ECM often takes the form of jamming. Self-protecting (defensive) ECM includes using blip enhancement and jamming of missile terminal homers.

The Flyvefisken-class patrol vessels are warships of the Royal Danish Navy. The class is also known as the Standard Flex 300 or SF300 class. The four vessels sold to the Portuguese Navy are locally referred as Tejo class.

Military aviation is the use of military aircraft and other flying machines for the purposes of conducting or enabling aerial warfare, including national airlift capacity to provide logistical supply to forces stationed in a theater or along a front. Airpower includes the national means of conducting such warfare, including the intersection of transport and war craft. Military aircraft include bombers, fighters, transports, trainer aircraft, and reconnaissance aircraft.

An acoustic torpedo is a torpedo that aims itself by listening for characteristic sounds of its target or by searching for it using sonar. Acoustic torpedoes are usually designed for medium-range use, and often fired from a submarine.

Anti-submarine mortars are artillery pieces deployed on ships for the purpose of sinking submarines by a direct hit with a small explosive charge. They 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.

The Mark 24 mine is an air-dropped passive acoustic homing anti-submarine torpedo used by the United States during the Second World War. It entered service in March 1943 and remained in use with the US Navy until 1948. Approximately 4,000 torpedoes were produced, with 204 ultimately being deployed during the war. As a result of its use, 37 Axis submarines were sunk and a further 18 were damaged. The torpedo was also supplied to the British and Canadian forces. The deceptive name of "Mark 24 Mine" was deliberately chosen for security purposes, to conceal the true nature of the weapon.

Anti-submarine warfare is a branch of underwater warfare that uses surface warships, aircraft, or other submarines to find, track, and deter, damage, or destroy enemy submarines.

The Rothesay class, or Type 12M frigates were a class of frigates serving with the Royal Navy, South African Navy and the Royal New Zealand Navy.

The People's Liberation Army Navy (PLAN) is the naval branch of the People's Liberation Army (PLA), the armed forces of the People's Republic of China. The PLAN force consists of approximately 250,000 men and over a hundred major combat vessels, organized into three fleets: the North Sea Fleet, the East Sea Fleet, and the South Sea Fleet.

An aerial torpedo, airborne torpedo or air-dropped torpedo is a naval weapon, a torpedo, that an aircraft—fixed-wing aircraft or helicopter—drops in the water, after which the weapon propels itself to the target. First used in World War I, air-dropped torpedoes were used extensively in World War II, and remain in limited use. Aerial torpedoes are generally smaller and lighter than submarine- and surface-launched torpedoes.

An anti-submarine missile is a standoff anti-submarine weapon. Often a variant of anti-ship missile designs an anti-submarine systems typically use a jet or rocket engine, to deliver: an explosive warhead aimed directly at a submarine; a depth charge, or; a homing torpedo that is carried from a launch ship, or other platform, to the vicinity of a target.

The Audace-class destroyers were two guided missile destroyers built for the Italian Navy during the Cold War. An improvement of the Impavido class, these ships were designed for area air defence and also had a heavy gun armament. They were fitted with contemporary American radars and sonars, but also, as the next Italian ships, all the modern weapons made by Italian industry of the time, such torpedoes, helicopters and guns. Also some indigenous radars were fitted.

Naval tactics play a crucial role in modern battles and wars. The presence of land, changing water depths, weather, detection and electronic warfare, the speed at which actual combat occurs and other factors — especially air power — have rendered naval tactics essential to the success of any naval force.

The AUM-N-6 Puffin, also known as Kingfisher F and AUM-6, was an anti-ship and anti-submarine missile developed for use by the United States Navy in the late 1940s. Pulsejet-powered and intended to allow an aircraft to launch a torpedo or bomb from stand-off range, it was flight-tested but failed to enter operational service.

## References

1. Blair, Clay, Silent Victory (Vol.1), The Naval Institute Press, 2001
2. . Lanning, Michael Lee (Lt. Col.), "Senseless Secrets: the failures of U.S. Military Intelligence, from George Washington to the present", Carol Publishing Group, 1995
• 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
• Preston, Anthony, The World's Greatest Submarines", Greenwich Editions, 2005.