Since 1998, TNO Defence, Security and Safety has performed operational analysis with the Underwater Warfare Testbed, which provides an environment for evaluation and validation of systems, concepts, and tactics. On top of this testbed the Torpedo Defence System TestBed has been built to simulate torpedoes, torpedo detection systems and torpedo countermeasures. Studies are performed in a research programme in which knowledge in this field is acquired to support the Royal Netherlands Navy in the procurement of new torpedoes and torpedo defence systems. This paper focuses on the most recent studies into the use of existing sonar systems (towed, hull mounted and dipping) to detect torpedoes. The detection performance results are used in the Area Torpedo Defence study to determine the composition of ship formations, which are in transit or operate in expeditionary operations including sea basing. Furthermore, the deployment of torpedo countermeasures in two different torpedo defence concepts is investigated.