The Army’s 1935 requirement pitted three prototypes against each other: Nakajima’s Ki-27, the Mitsubishi Ki-33 en de Kawasaki Ki-28. The Kawasaki entry was faster in a straight line, but the Army’s fighter pilots valued manoeuvrability above speed, and the Ki-27 turned tighter than either rival. Nakajima had also refined the wing across several prototypes, settling on a broad, low-loading planform that gave the fighter its famous agility. It was ordered into production and formally adopted as the Army Type 97 Fighter on 28 December 1937 — the aircraft that finally brought the Japanese Army’s fighter arm into the monoplane age.

By the late 1930s retractable landing gear was becoming standard on front-line fighters, so the Ki-27’s fixed, spatted wheels marked it as a transitional design. The choice was deliberate. On a lightweight fighter that cruised well below the speeds where undercarriage drag dominates, Nakajima calculated that the weight, cost and mechanical risk of a retracting system outweighed the small speed gain. The spats streamlined the wheels enough to keep performance respectable, and the fixed gear was rugged and simple to service from rough forward strips in Manchuria and China. Nakajima’s very next fighter, the Ki-43 Hayabusa, finally adopted retractable gear.

The Ki-27 was designed around a doctrine that prized the turning dogfight, and every kilogram mattered to that goal. So it carried no armour plate for the pilot and no self-sealing fuel tanks, and its firepower was limited to two rifle-calibre 7.7 mm guns. Against Soviet and Chinese aircraft of the late 1930s this was tolerable. Against the heavier guns and rugged construction of Allied fighters from 1942 — and against opponents who refused to turn with it and instead used speed and diving attacks — the Nate’s fragility became decisive. A single burst was often enough to bring one down. It is the classic early-war Japanese bargain: superb agility, paid for in survivability.

The Ki-27 was a wartime Imperial Japanese Army product, procured inside a state war economy and never sold on an open market, so no dependable unit price or cost-per-flight-hour figure survives in the public record. Nor do standard English-language references — History of War, WW2DB, Military Factory — carry one. Any precise dollar or yen figure attached to a Nate should be treated as an unsourced estimate. Even the total built is uncertain: the most-cited number is about 3,368, but the split between Nakajima and the Manchurian firm Mansyu, and the overlap with the closely related Ki-79 trainer, means totals up to roughly 3,400 appear in the literature.