The Mitsubishi J2M Raiden was constructed as an interceptor with high horizontal speed and climb rate. Achieving good performance in the aforementioned parameters resulted in worse maneuverability, but it was still a very successful design. The Raidens entered service too late to change the face of the war with the United States, but they were nevertheless the most effective fighters against the USAAF's B-29s.   The specification defined in September 1939 contained exact requirements for the newly constructed machine. The new fighters were to be able to reach a speed of 600 km/h at an altitude of 6,500 m, and the engine was to withstand full power for 45 minutes. The time of ascent to the ceiling of 6,500 m was to be no more than 5.5 minutes. The armament was to consist of two 20 mm cannons and two 7.7 mm machine guns.