Foxer

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Foxer, was the codename for a British built acoustic decoy, used to confuse German acoustic homing torpedoes like the G7es torpedo during the Second World War. A US version codenamed FXR was deployed in 1943. A Canadian version was also built called the CAT (Counter-Acoustic Torpedo). It was replaced in US service by the Fanfare noisemaker.

[edit] Description

The Foxer consisted of one or more 3000 lb (1,360 kg) arrangements of hollow metal pipes with holes cut in them. These were towed through the water about 200 meters behind the boat. The water rushing through the holes and the pipes banging together created cavitation noise, much greater than that coming from the ships propeller. This worked because the German homing torpedoes were tuned to home in on the sound frequencies generated by cavitation, and further home in on the loudest cavitation sound.

The Germans U-boat crews called it the circular saw or Rattelboje (an onomatopoeic word meaning rattle buoy), 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 14 knots (26 km/h) and because of the noise it effectively rendered the towing ships sonar 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 convoys.

In the closing stages of the war the Germans developed the T11 Zaunkoenig II. It was designed to ignore towed decoys and noisemakers. However, it was never fired.