by the Japanese Imperial Navy, mostly because of inefficient submarine deployment. The Second World War During the Second World War tactical developments became even more closely tied to the development of new weapons and technologies. The war saw the first large-scale tactical use of hydrophones, sonar (or ASDIC) and radar, and the development of new technologies such as high-frequency direction finding (HF/DF). In the North Sea and Atlantic, Germany lacked the strength to challenge the Allies for command of the sea. Instead, German naval strategy relied on commerce raiding using capital ships, armed merchant cruisers, submarines and aircraft. The Allies immediately introduced a convoy system for the protection of trade that gradually extended out from the British Isles, eventually reaching as far as Panama, Bombay and Singapore. In the Mediterranean, Britain and Italy fought a conventional naval war for command of the sea. The need to provide capital ships with the anti-submarine protection of a destroyer screen and air cover from an aircraft carrier led to the increasing use of ad hoc task forces, composed of whichever ships were available for a particular operation. Later in the war however, anti-submarine warfare was perfected to a large degree by the Allies, meaning that much more specialized ships and equipment were deployed in convoys with the express purpose of detecting and destroying German (and later Japanese) submarines. Impact of aircraft on tactics The development of air power led to further tactical changes, including the emergence of aircraft carriers and the development of naval air fleets. The employment of land-based and carrier-based aircraft during the Second World War showed that command of the seas rested in great part on control of the air above it. Off Norway in the spring of 1940 and in the English Channel in the summer of that year, the German Luftwaffe demonstrated that the British could not maintain command of the sea in daytime without command of the air. In the following year, the arrival of Luftwaffe squadrons in the Mediterranean reversed the British ascendancy in the theatre by neutralizing the British dominance at sea. Development of the wolf pack With the immediate introduction of convoy by the Allies at the start of the Second World War, the German submarines (known as U-boats) operating against Allied trade in the Atlantic were driven to adopt new tactics. Until the last year of the war, almost all U-boats were diesel-powered,