The Torpedo Countermeasures Transmitting Set AN/SLQ-25A, commonly referred to as Nixie, is a passive, electro-acoustic decoy system used to provide deceptive countermeasures against acoustic homing torpedoes. The AN/SLQ-25A employs an underwater acoustic projector housed in a streamlined body which is towed astern on a combination tow/signal-transfer coaxial cable. An onboard generated signal is used by the towed body to produce an acoustic signal to decoy the hostile torpedo away from the ship. The AN/SLQ-25A includes improved deceptive countermeasures capabilities. The AN/SLQ-25B includes improved deceptive countermeasures capabilities, a fiber optic display LAN, a torpedo alertment capability and a towed array sensor.
Modern acoustic towed decoys, such as the AN/SLQ-25 NIXIE and the older T-MK6 FANFAIR, employ electronic or electromechanical means to produce the required signals. The system provides an alternate target diversion for an enemy acoustic homing torpedo by stringing on cable a "noise maker", aft of the ship, which has the capability of producing a greater noise than the ship; thereby diverting the incoming torpedo from the ship to the "fish". The towed device receives the torpedoes ping frequency, amplifies it 2 to 3 times and sends it back to lure the torpedo away from the ship. They may be used in pairs or singularly.
Operators are cautioned not to attempt MC transmission with less then 1000 feet of fiber optic tow cable (fotc) deployed, and MC transmission should be terminated before retrieval of FOTC commences. On below deck installations, the cable guide doors, if installed, must be closed whenever more than 50 feet of cable is paid out. Open doors mat cause the FOTC to ride out of the sheave and become caught between the sheave and keeper roller, seriously damaging the FOTC. Although the tech manual states the launch/retrieval speeds for the system are between 10-25 knots, it is strongly suggested not to exceed 15 knots. At speeds in excess of 15 knots damage to tow cable can occur on some platforms. (DD, DDG 994 class and CG 47 class). The emergency non-powered payout procedure should only be used when power is lost to the winch and the tactical situation dictates deployment of the torpedo countermeasures system. Winch speed must be carefully controlled by braking during non-powered payout operations. If not monitored the winch will rotate at an extremely dangerous rate.
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