Bold (decoy)

German WWII sonar decoy

Post-war U.S. diagram of a Bold canister

Bold (also called Bolde, a term derived from kobold) 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 (English: "pill thrower"). 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.[1]

The Royal Navy called it SBT (Submarine Bubble Target).

## See also

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* Sieglinde

## References

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1. ^ Morgan, Daniel; Taylor, Bruce (2011). U-Boat Attack Logs: A Complete Record of Warship Sinkings from Original Sources 1939–1945. Seaforth Publishing. pp. xi. ISBN 978-1-84832-118-2.

## External links

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* Sonar decoys at uboataces.com

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