Group : Decoy Systems
Status : Active
Also Known As : S2170, SSTD, Surface Ship Torpedo Defence
Origin : United Kingdom
Contractor : Ultra Electronics Holdings Plc
Initial Operational Capability (IOC) : 2005
Total Production : 65
Unitary Cost : USD $1.9 million

Ultra Electronics' Surface Ship Torpedo Defence (SSTD) is an anti-torpedo system designed for use on British ships ranging from Royal Navy's surface fighting ships to fleet auxiliary support ships. The system entered service in early 2005 installed onto HMS Westminster Type 23-class frigate and was scheduled for integration onto 65 surface ships owned by the United Kingdom. The SSTD program is valued at £65 million and has an expected service life of 25 years. The UK MoD projects to conclude integration work over the next two years. Each ship takes three to four weeks to get the upgrade.

SSTD protects surface ships from underwater torpedo attacks by deploying highly sensitive acoustic sensors and providing the best solution to ship's commander ranging from maneuvering the ship putting her away from danger to deploying torpedo countermeasures/decoys that would divert the incoming threat. The acoustic sensors are towed some distance behind the ship and can identity and locate with pin-point accuracy an incoming torpedo. UK frigates, aircraft carriers and oilers will be protected by SSTD before the end of 2007 replacing sonar 2070.

Sea Sentor, also known as SSTD or Sonar 2170, was developed by Ultra Electronics for the Royal Navy. This system has some degree of technological commonality with the US Navy's TRAPE DCL torpedo defense system also developed by Ultra.