The US Navy has decided (finally) to design and buy a torpedo defense system including an anti-torpedo torpedo. The WSQ-11 system would deal with torpedoes within 5,000 yards of the ship. The program is primarily intended to defend large ships such as aircraft carriers, amphibious carriers, and sealift transport ships. The anti-torpedo torpedo is to be 6.25 inches in diameter, which would fit into the existing decoy launchers used by large surface ships and US submarines. The anti-torpedo torpedo uses both active and passive sonar to find its target, and seeks to get close enough that its high explosive warhead can destroy or disable it. The system would be effective against straight-running, wake homing, and wire-guided torpedoes.--Stephen V Cole