Nakajima began development of the Ki-44 in 1940 as a pure interceptor with emphasis being placed on airspeed and rate of climb rather than maneuverability, a departure from the usual Japanese standards. The Japanese Army Air Force specification called for a maximum speed of 600 km/h (370 mph) at 4,000 m (13,130 ft), to be attained in five minutes. A set of Ki-43-like "butterfly" combat flaps was fitted for improved maneuverability. Armament consisted of a pair of 7.7 mm (.303 in) and a pair of 12.7 mm (.50 in) machine guns.