The Battle of the Atlantic 1939-1945 A24712

Foxer was the code name for a

British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...

built acoustic decoy used to confuse

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...

acoustic homing

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, su ...

es like the G7 torpedo during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. A US version codenamed FXR was deployed at the end of September 1943 on all transatlantic escort vessels. A

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

version was also built called the CAAT (Canadian Anti-Acoustic Torpedo) device. It was replaced in US service by the

Fanfare A fanfare (or fanfarade or flourish) is a short musical flourish which is typically played by trumpets, French horns or other brass instruments, often accompanied by percussion. It is a "brief improvised introduction to an instrumental perfo ...

noisemaker. The device consisted of one or two noise-making devices towed several hundred metres astern of the ship. The noise makers mechanically generated a far louder

cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...

noise than the ship's propellers. This noise distracted the acoustic torpedoes away from the rear of the ship into a circling pattern around the noise maker until the torpedo ran out of fuel. The downside of the ''Foxer'' was that it also rendered the ship's own

ASDIC 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 or ...

ineffective and concealed any other U-boat nearby that could approach the convoy. Nevertheless, the FXR countermeasure proved to be highly effective in decoying German acoustic torpedoes. Of the c. 700 fired

G7es The G7es (T5) ''"Zaunkönig"'' ("wren") was a passive acoustic torpedo employed by German U-boats during World War II. It was called the GNAT (German Navy Acoustic Torpedo) by the British. Description The forerunner of the ''Zaunkönig'' was t ...

torpedoes about only 77 had found their aim.

Development

By 1943

Allied An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called ...

intelligence sources indicated that Germany had produced a passive

acoustic homing Acoustic homing is a system which uses the acoustic signature (sound) of a target to guide a moving object, such as a torpedo. Acoustic homing can be either passive or active in nature. Using passive homing, the system is designed to move either t ...

torpedo, which homed on the sound produced by a ship's

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

as it moved through the water. To counter this threat various countermeasures were considered. There was already a towed noise maker developed to mine-sweep for

acoustic mine An acoustic mine is a type of naval mine which monitors audio activity in its vicinity. Depending on its design, it will either passively listen to its environment, depending only on the noise that is made by passing ships or actively send out audi ...

s, consisting of two steel bars fixed parallel, with a gap between them to allow water to flow between, and towed perpendicular to the flow of water. The water flowing between the two bars caused them to flex and bang together generating far more noise than the towing ship above 1 kHz. This noisemaker produced around 20

decibel The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...

s more noise than the towing ship, and would last for around 25 hours when towed at 12 knots. The US developed this existing noise-maker into the FXR, which was to be towed singly around 500 feet behind the ship. This entered production by July 1943. The single noise-maker however would work effectively only if the torpedo was equally sensitive to sounds from both the front and rear. If a torpedo passed directly over the noise-maker from the rear the ship itself would be directly ahead, if the torpedo had a reduced sensitivity to noise from behind, it might ignore the greater output from the noise-maker, and proceed to home on the ship. After successful attacks on ships in Convoy ONS 18 and

Convoy ON 22 A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support and can help maintain cohesion within a unit. It may also be used ...

in which nine ships were sunk, more detailed studies were begun into the torpedo behaviour. These studies revealed that against a torpedo with reduced sensitivity to the rear (described by its sensitivity pattern as a Cosθ torpedo), a single towed noise-maker would not be sufficiently effective.

Description

The Foxer consisted of one or more arrangements of hollow metal pipes with holes cut in them. These were towed through the water about behind the ship. The water rushing through the holes and the pipes banging together created

noise, much greater than that coming from the ship's propeller. This worked because the German homing torpedoes were tuned to home in on the sound frequencies generated by cavitation, and on the loudest cavitation sound. The German

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 role ...

crews called it the ''Kreissäge'' (

circular saw A circular saw is a power-saw using a toothed or abrasive disc or blade to cut different materials using a rotary motion spinning around an arbor. A hole saw and ring saw also use a rotary motion but are different from a circular saw. ''Cir ...

) or ''Rattelboje'' (''rattle

buoy A buoy () is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents. Types Navigational buoys * Race course marker buoys are used for buoy racing, the most prevalent form of yac ...

'') and estimated the volume of noise generated by Foxer at 10 to 100 times greater than that generated by a ship. The limitations of the system were that it could not be towed faster than and because of the noise it effectively rendered the towing ship's

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 navigation, navigate, measure distances (ranging), communicate with or detect o ...

useless. The drums also wore out quickly and the sound could be heard underwater over a long distance giving away the position of the towing ship to U-boats searching for

convoy A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support and can help maintain cohesion within a unit. It may also be used ...

s. In the closing stages of the war the Germans developed the T11 ''Zaunkönig II'' torpedo, designed to ignore towed decoys and noisemakers. However, it was never actually employed in wartime as Germany had surrendered by the time testing was fully completed.

Footnotes

References

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External links

* * {{cite web , url=http://stonebooks.com/archives/030202.shtml , title=Second World War Books Review , access-date=December 4, 2014 , author=Campbell, John Sonar decoys