A sonar decoy is a device for

decoy A decoy (derived from the Dutch ''de'' ''kooi'', literally "the cage" or possibly ''ende kooi'', " duck cage") is usually a person, device, or event which resembles what an individual or a group might be looking for, but it is only meant to lur ...

ing

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects on ...

. Most are released from submarines to act as a false target.

Submarine decoys

The first submarine decoys were the German

Bold In typography, emphasis is the strengthening of words in a text with a font in a different style from the rest of the text, to highlight them. It is the equivalent of prosody stress in speech. Methods and use The most common methods in ...

fitted to

U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare ro ...

s 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.

Torpedo decoys

Decoys were also used by surface ships to decoy the developing acoustic torpedoes. These were usually towed behind the host.

Example decoys

Bubble decoys

Reflective bubble targets *

* Sieglinde

Hammer and explosive decoys

These were intended to swamp the listening device with noise * Siegmund

Signature decoys

* AN/SLQ-25 Nixie * Mobile submarine simulator

Towed decoys

* Foxer, a British towed decoy to decoy acoustic torpedoes away from surface ships. Also used by the US as FXR and the Canadians as CAT. * T-Mk 6 Fanfare, US development of Foxer

References

External links

* 01 U-boats {{weapon-stub