(also called , a term derived from ''
kobold
A kobold (; ''kobolt'', ''kobolde'', cobold) is a general or generic name for the household spirit (''hausgeist'') in German folklore.
It may invisibly make noises (i.e., be a poltergeist), or helpfully perform kitchen chores or stable work. ...
'') was a
German sonar decoy, used by
U-boat
U-boats are Submarine#Military, naval submarines operated by Germany, including during the World War I, First and Second World Wars. The term is an Anglicization#Loanwords, anglicized form of the German word , a shortening of (), though the G ...
s during the
Second World War
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
from 1942 onwards. It consisted of a metal canister about in diameter filled with
calcium hydride. It was launched by an ejector system
colloquially referred to as (English: "
pill thrower"). When mixed with
seawater
Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximat ...
, 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 . The device lasted 20 to 25 minutes. It replicated the echo of an
Asdic-sonar submarine contact.
The
Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
called it SBT (Submarine Bubble Target).
See also
*
References
External links
Sonar decoys at uboataces.com
Sonar decoys
Weapons countermeasures
U-boats
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