The present pre-study deals with anti-torpedo defence systems with a focus on super-cavitating projectiles and rockets. The purpose of such systems is to deliver a last-minute defence countermeasure to counter a torpedo attack. Based on concept design and analysis of five different anti-torpedo defence systems, and also taking previous analysis of anti-torpedo torpedo (ATT) into account, an assessment of design aspects has been carried out. It is assumed that high-frequency active sonars are used for target tracking, which is complemented by already existing passive sonar systems on the submarine. The alternative, a projectile with very high initial speed, about 1500 m/s, results in large system weights which complicates the submarine integration. In addition, the requirements on targeting systems are challenging for the alternatives without explosives. Other alternatives based on projectiles or rockets having reduced speed and equipped with explosives seems preferable. A super cavitating rocket equipped with propulsion and explosives will reduce the total system weight and targeting requirements. The rocket can also be equipped with some limited guidance capability and the travelled distance can be extended by gas generation or the use of a two-step engine. The above mentioned and other possible measures increase the complexity of the system and imply a substantial development effort. A continuation of the research is recommended, which encompasses design of a super-cavitating projectile or rocket, and trials to study the stability and hit accuracy of the projectile or the rocket. ATT is an alternative for self-protection. Integration in a submarine system is facilitated by ATT discharge tubes being relatively small, adding less additional weight and is associated with great flexibility regarding range, position of discharge tubes and possible communication by thread. It is also of interest to study more in detail machine gun systems with underwater ammunition for surface ships. However, an ATT-system with large range is required to protect ships during escort missions.