Anti-submarine warfare (ASW) plays an important part in 20th-century conflict. Countering the potent threat of nuclear-powered and conventional submarines, it deploys technology of a high order, and uses platforms, sensors and weapons which operate under, on and above the sea. But the potential of submarines for harm across a wide spectrum of peace and warfighting, ranging from strategic nuclear deterrence to special forces operations, is still enormous. Thus the efficacy and significance of ASW remains an important part of strategy, maritime technology and tactics.