and began service in August 1942. The greatest developmental problem was in bringing the weight down to that allowable for an aircraft; was eventually achieved. Intended for both air and surface search, the Type 64 operated at 2 m (150 MHz) with a peak power of 3 to 5 kW and a pulse width of 10 ms. It used a single Yagi antenna in the nose of the aircraft and dipoles on each side of the fuselage, and could detect large surface vessels or flights of planes at up to . This set was initially used on H8K-class four-engine flying boats, then later on a variety of mid-sized attack planes and torpedo bombers. It was by far the most used airborne radar, with about 2,000 sets produced. Development continued on lighter-weight systems at the ONATD. The Type N-6 weighing was available in October 1944, but only 20 sets were built. This was a 1.2 m (250-MHz), 2 kW experimental set intended for a single-engine, three-place (pilot, gunner, and radar operator) fighter aircraft. Another was the Type FM-3; operating at 2 m (150 MHz) with 2 kW peak-power, this weighed 60 kg and had a detection range up to . Specifically designed for the Kyūshū Q1W Tokai, a new two-engine three-place anti-submarine aircraft, about 100 sets were built, going into service in January 1945. With assistance from the NTRI and Yoji Ito, the ONATD also developed Japan's only airborne microwave radar. Designated FD-2 (sometimes FD-3), this was a magnetron-based, 25 cm (1.2-GHz), 2 kW set weighing about 70 kg. It could detect aircraft at a range between , satisfactory for close-range night-fighter aircraft such as the Nakajima J1N1-S "Gekko". It used four Yagi antennas mounted in the nose area; separate elements for transmit and receive were skewed for searching. Unlike in the air warfare in Europe, there were few night-fighter aircraft used by Japan; consequently, it was mid-1944 before the Type FD-2 was put into use. Some 100 sets were manufactured. When magnetrons were being developed in Japan, the initial primary application was intended to be power transmission, not radar. As these devices increased in output energy, their application for a weapon became apparent. For research in special weapons, a large facility was built in Shimada. In 1943, a project in developing a Ku-go (Death Ray) using magnetrons began. By the end of the war, magnetrons developing 100 kW continuous power