The Nakajima Ki-4 was a biplane design with staggered wings and fixed divided landing gear. It was powered by one 477 kW (640 hp) Nakajima Ha-8, nine-cylinder, air-cooled radial engine. Maximum speed was 300 km/h (190 mph) and maximum take-off weight 2,500 kg (5,500 lb). It was armed with up to four 7.7 mm (0.303 in) machine guns, two fixed to fire forward, synchronized with the propeller, and one or two more mounted dorsally on a flexible mount. The maximum bomb load was 50 kg (110 lb).
The first Ki-4s began equipping Imperial Japanese Army Air Force units in 1935 and were an active part of Japanese fighter squadrons for a number of years thereafter. The Ki-4s saw substantial service in the early stages of the Second Sino-Japanese War from 1938. They also functioned as light ground-attack aircraft in the support of advancing Japanese ground troops. However, these biplanes were vulnerable to even the oldest and slowest moving enemy fighters. By the time of the entry of Japan into World War II, the Ki-4s were regarded as obsolete. A number were still retained for use in the supply and liaison role from 1941, and others were transferred to the Manchukuo Air Force, but those that had not been lost in service served briefly as elementary trainers or target tugs before being scrapped. All of the Ki-4s were removed from active service by 1943.
Two Ki-4s were tested as seaplanes, one with twin floats and the other with one main and two stabilizing floats, but neither version was placed into production.[2]
