Foxer

Foxer was the code name for a British-built acoustic decoy used to confuse German acoustic homing torpedoes like the G7 torpedo during the Second World War. A US version codenamed FXR was deployed at the end of September 1943 on all transatlantic escort vessels. A Canadian version was also built called the CAAT (Canadian Anti-Acoustic Torpedo) device. It was replaced in US service by the Fanfare 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 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 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 torpedoes about only 77 had found their aim. By 1943 Allied intelligence sources indicated that Germany had produced a passive acoustic homing torpedo, which homed on the sound produced by a ship's propeller 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 mines, 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 decibels 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.