Wikipedia
Foxer decoy float resting on the top of the depth charge racks of HMS Hind (U39)
]] 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 in 1943. A Canadian version was also built called the CAT (Counter-Acoustic Torpedo). It was replaced in US service by the Fan fare noisemaker.
The device consisted of one or two noise making devices towed several hundred metres behind the ship. The noise makers mechanically generated huge amounts of noise, far more than produced by the ship itself. This noise seduced the simple guidance mechanisms of acoustic torpedoes away from the rear of the ship into a circling pattern around the noise maker until the torpedo ran out of fuel.
Usage examples of "foxer".
The Foxer also had disadvantages in that it impaired underwater acoustic position-finding, so reducing the offensive capability of the destroyers.
The Foxer was introduced and we in U 333 were the first who got to hear of it.
In order to out manoeuvre the Foxer we, in our turn, developed a new improved acoustic torpedo which steered for the Foxer and ran beneath it.