 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.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.