wars but this was a passive form of harbour defense that depended on detecting the magnetic field of submarines by the use of long lengths of cable lain on the floor of the harbour. Indicator loop technology was quickly developed further and deployed by the US Navy in 1942. By then, there were dozens of loop stations around the world. Sonar was far more effective and loop technology for ASW purposes was discontinued shortly after the conflict's end. The use and improvement of radar technology was one of the most important elements in the fight against submarines. Locating submarines was the first step in being able to defend against and destroy them. Throughout the war, Allied radar technology was much better than their German counterparts. German U-boats struggled to have proper radar detection capabilities and keep up with the successive generations of Allied airborne radar. The first generation of Allied airborne radar used a 1.7 meter wavelength and had a limited range. By the second half of 1942 the "Metox" radar detector was used by U-boats to give some warning from airborne attack. During 1943, the Allies began to deploy aircraft equipped with new cavity magnetron-based 10-centimeter wavelength radar (ASV III), which was undetectable by "Metox", in sufficient numbers to yield good results. Eventually the "Naxos" radar detector was fielded that could detect 10-cm wavelength radar, but it had a very short range and only gave a U-boat limited time to dive. Between 1943 and 1945, radar equipped aircraft would account for the bulk of Allied kills against U-boats. Allied anti-submarine tactics developed to defend convoys (the Royal Navy's preferred method), aggressively hunt down U-boats (the U.S. Navy approach), and to divert vulnerable or valuable ships away from known U-boat concentrations. During the Second World War, the Allies developed a huge range of new technologies, weapons and tactics to counter the submarine danger. These included: Vessels Allocating ships to convoys according to speed, so faster ships were less exposed. Adjusting the convoy cycle. Using operations research techniques, analysis of convoy losses over the first three years of the war showed that the overall size of a convoy was less important than the size of its escorting force. Therefore, escorts could better protect a few large convoys than many small ones. Huge construction programmes to mass-produce the small warships needed for convoy defense, such as corvettes, frigates, and destroyer escorts. These