Sonar decoy

Bold decoy pellet

A sonar decoy is a device for decoying sonar. Most are released from submarines to act as a false target.

Submarine decoys[]

Bold launch tube, in the stern compartment of a type XXI U-boat

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.

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

Bold^[1]
Sieglinde

Hammer and explosive decoys[]

These were intended to swamp the listening device with noise

Siegmund

Signature decoys[]

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[]

^ Gannon, Robert (2009). Hellions of the Deep. Penn State Press. pp. 132–133. ISBN 978-0271038407.

External links[]

"Sonar decoys". uboataces.com.

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[1] Gannon, Robert (2009). Hellions of the Deep. Penn State Press. pp. 132–133. ISBN 978-0271038407.

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