A sonar decoy is a device for decoying sonar. One may be released from a submarine or a surface vessel. A decoy acts as false targets for human operators and/or sonar-homing weapons such as acoustic torpedoes. Many count as a type of torpedo defence.
The first submarine decoys were the German Bold fitted to U-boats of World War II. These were a pellet of calcium hydride in a simple metal container. On contact with sea water, the calcium hydride decomposed to produce a trail of hydrogen gas bubbles that acted as a bubble curtain and reflected ASDIC impulses to produce a false target. The container trapped hydrogen and floated, with a crude spring valve to maintain buoyancy to keep it at a constant depth.
Later decoys, such as Sieglinde, were motorised and could deploy their false target away from the host submarine, increasing safety.
Decoys were also used by surface ships to decoy the developing acoustic torpedoes. These were usually towed behind the host.
Reflective bubble targets that produce an active return
Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.
The Mark 48 and its improved Advanced Capability (ADCAP) variant are American heavyweight submarine-launched torpedoes. They were designed to sink deep-diving nuclear-powered submarines and high-performance surface ships.
Type 53 is the common name for a family of 53 cm torpedoes manufactured in Russia, starting with the 53-27 torpedo and continuing to the modern UGST (Fizik-1), which is being replaced by the Futlyar.
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.
Acoustic homing is the process in which a system uses the sound or acoustic signals of a target or destination to guide a moving object. There are two types of acoustic homing: passive acoustic homing and active acoustic homing. Objects using passive acoustic homing rely on detecting acoustic emissions produced by the target. Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target. The signal detected is then processed by the system to determine the proper response for the object. Acoustic homing is useful for applications where other forms of navigation and tracking can be ineffective. It is commonly used in environments where radio or GPS signals can not be detected, such as underwater.
A sonobuoy is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on the water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater.
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.
Radar jamming and deception is a form of electronic countermeasures (ECMs) that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blanket the radar with signals so its display cannot be read are normally known as jamming, while systems that produce confusing or contradictory signals are known as deception, but it is also common for all such systems to be referred to as jamming.
The AN/SLQ-25 Nixie and its variants are towed torpedo decoys used on US and allied warships. It consists of a towed decoy device (TB-14A) and a shipboard signal generator. The Nixie is capable of defeating wake-homing, acoustic-homing, and wire-guided torpedoes. The decoy emits signals to draw a torpedo away from its intended target.
Prairie-Masker is a radiated noise reduction system fitted to some western warships, including the Oliver Hazard Perry-class frigates, Spruance and Arleigh Burke-class destroyers, and the Ticonderoga-class cruisers of the US Navy. The system was also installed during the 1960s on a limited number of post WWII Guppy III modified, and later diesel submarines.
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.
Bold was a German sonar decoy, used by U-boats during the Second World War from 1942 onwards. It consisted of a metal canister about 10 cm (3.9 in) in diameter filled with calcium hydride. It was launched by an ejector system colloquially referred to as Pillenwerfer. When mixed with seawater, the calcium hydride produced large quantities of hydrogen, which bubbled out of the container, creating a false sonar target. A valve opened and closed, holding the device at a depth of about 30 m (98 ft). The device lasted 20 to 25 minutes. It replicated the echo of an Asdic-sonar submarine contact.
Anti-submarine warfare is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations are typically carried out to protect friendly shipping and coastal facilities from submarine attacks and to overcome blockades.
The Mark 37 torpedo is a torpedo with electrical propulsion, developed for the US Navy after World War II. It entered service with the US Navy in the early 1950s, with over 3,300 produced. It was phased out of service with the US Navy during the 1970s, and the stockpiles were sold to foreign navies.
The Type 039 submarine is a class of diesel-electric submarines of the People's Liberation Army Navy. The class is the first diesel-electric submarine to be made in China and also the first Chinese made diesel-electric submarine to use the teardrop hull shape. Altogether thirteen vessels were completed to the Song Class design between 1999 and 2006, with three variants as the type developed.
The term acoustic signature is used to describe a combination of acoustic emissions of sound emitters, such as those of ships and submarines. In addition, aircraft, machinery, and living animals can be described as having their own characteristic acoustic signatures or sound attributes, which can be used to study their condition, behavior, and physical location.
Geophysical MASINT is a branch of Measurement and Signature Intelligence (MASINT) that involves phenomena transmitted through the earth and manmade structures including emitted or reflected sounds, pressure waves, vibrations, and magnetic field or ionosphere disturbances.
Torpedo defence includes evasive maneuvers, passive defense like torpedo belts, torpedo nets, torpedo bulges, and sonar torpedo sensors, "soft-kill" active countermeasures like sonar decoys and sonar jammers, and "hard-kill" active defenses, like anti-torpedo torpedoes similar in idea to missile defense systems. Surface Ship Torpedo Defense and Countermeasure Anti-Torpedo systems are highly experimental and the US Navy ended trials on them in 2018.
INS Kadmatt (P29) is the second of four anti-submarine warfare corvettes built for the Indian Navy by the Garden Reach Shipbuilders and Engineers, of Kolkata, under Project 28. She was inducted into the Eastern Naval Command of the Indian Navy.
BNS Joyjatra is a Type 035G diesel electric submarine of the Bangladesh Navy. She is one of the first two submarines of the Bangladesh Navy.
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