Due to the proliferation of submarines and the improvements in torpedo technology (endurance, intelligence), naval surface vessels experience an ever increasing torpedo threat level. To counter this threat, torpedo defence systems have been developed. However, the torpedo defence technology (often only based on soft-kill countermeasures like decoys and jammers) has lacked behind the torpedo technology, which has become more and more intelligent and able to recognize and avoid soft-kill countermeasures. Moreover, wake-homing and multi-modal torpedoes are conceptually soft-kill insensitive. Only recently the development of torpedo hard-kill based on anti-torpedo-torpedo (ATT) was started. ATT based torpedo defence can potentially counter all threat torpedoes including the modern and wake-homing types. ATT technology is still under development.