OVERVIEW: The ZLQ‑2B is an expendable acoustic torpedo decoy deployed by Japanese submarines to protect against incoming acoustic-homing torpedoes. Designed for underwater use, it mimics submarine acoustic signatures when launched from 533 mm torpedo tubes.

DETAILS: The ZLQ‑2B comes standard aboard Japanese diesel-electric submarines such as the Sōryū (Type 201) and Taigei (Type 12) classes. After being launched through a 533 mm torpedo tube, it descends to operational depth (up to roughly 1.9 km) and activates acoustic emitters that simulate the host submarine’s machinery and propulsion noise . Its acoustic output creates a decoy target intended to lure incoming torpedoes away from the submarine.

This decoy is part of Japan’s layered underwater defense framework, complementing other countermeasures like bubble-screen noisemakers. Deployable in rapid sequence, ZLQ‑2B units are triggered via the submarine’s combat management system upon detecting acoustic threats. Once the decoy completes its active cycle, it sinks or drifts away to avoid compromising the submarine.

Its deployment enhances survivability by creating false targets and confusing torpedo guidance, giving the submarine time to execute evasive maneuvers or deploy additional defense systems.

FONCTION:
Detect incoming torpedo threat using onboard sonar systems.
Launch the ZLQ‑2B decoy from a 533 mm torpedo tube.
Emit a submarine-like acoustic signature to attract and distract the torpedo.

SOURCE:
Jane’s Underwater Warfare Systems; Japanese Naval EW Documentation.