OVERVIEW: The S2170 Sea Sentor is a towed torpedo defense system developed by the UK for surface warships, functioning as a soft-kill countermeasure. It is designed to detect, classify, and decoy incoming acoustic-homing torpedoes using both towed and expendable acoustic decoys.

DETAILS: Developed by Ultra Electronics and introduced into Royal Navy service in 2004, the S2170—also known as Sonar 2170—is the standard Surface Ship Torpedo Defence (SSTD) system for Royal Navy surface combatants. The system integrates a towed passive sonar array, a flexible towed acoustic countermeasure body, and expendable acoustic decoys. Its sonar array detects incoming torpedoes and classifies threat parameters in real time, with automated deployment of countermeasures directed by onboard processing systems. The acoustic decoy mimics ship signatures to lure the torpedo away from the host vessel.

“S2170” is the Royal Navy designation; “Sea Sentor” is the export name for the same system.

FUNCTION: When a threat is detected, the towed array tracks the torpedo and cues automatic deployment of the flexible towed decoy. The decoy emits deceptive acoustic signals to divert the torpedo from the ship, and expendable decoys may be deployed to further confuse or saturate the seeker.

NOTE:
IOC: 2004 (S2170 Sea Sentor)
Operators: United Kingdom
Platforms: Type 23 frigate, Type 31 frigate (planned)

SOURCE:
UK Ministry of Defence Surface Ship Torpedo Defence datasheet ; Ultra Electronics: https://www.ultra.group/what-we-do/maritime/undersea-warfare/sea-sentor/ ; UK Defence Journal: https://ukdefencejournal.org.uk/royal-navy-type-31s-to-receive-ultra-sea-sentor-torpedo-defence-system/ ; Jane’s Underwater Warfare Systems