OVERVIEW: The FAJ is a floating, expendable acoustic jammer developed by Japan for use as a torpedo countermeasure. It is designed to divert acoustic homing torpedoes away from surface ships by generating false acoustic targets and jamming signals.

DETAILS: The FAJ (Floating Acoustic Jammer) is a soft-kill anti-torpedo decoy deployed from surface vessels of the Japan Maritime Self-Defense Force (JMSDF).

Once deployed into the water, the FAJ floats and begins emitting acoustic signals intended to mimic the signature of the launching ship or produce disruptive noise patterns to interfere with active and passive torpedo guidance systems. It is used to mislead or seduce incoming torpedoes away from the protected vessel. It is designed for both preemptive and reactive deployment in torpedo engagement scenarios.

SOURCE:
Japanese Ministry of Defense (MOD) Equipment Procurement Guidelines ; JMSDF Official Publications ; Naval Systems & Technology Japan ; National Institute for Defense Studies Japan (NIDS) ; Jane’s Underwater Warfare Systems