Bold (decoy)

{{Short description|German WWII sonar decoy}}

Image:Pillenwerfer.jpg

{{lang|de|Bold}} (also called {{lang|de|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 {{convert|10|cm|in||abbr=on}} in diameter filled with calcium hydride. It was launched by an ejector system colloquially referred to as {{lang|de|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 {{convert|30|m|ft|abbr=on}}. The device lasted 20 to 25 minutes. It replicated the echo of an Asdic-sonar submarine contact.{{Cite book |last1=Morgan |first1=Daniel |url=https://books.google.com/books?id=PB_OAwAAQBAJ&dq=World+War+II+bold+sonar+decoy+pillenwerfer&pg=PR11 |title=U-Boat Attack Logs: A Complete Record of Warship Sinkings from Original Sources 1939–1945 |last2=Taylor |first2=Bruce |publisher=Seaforth Publishing |year=2011 |isbn=978-1-84832-118-2 |pages=xi |language=en}}

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