The first significant Nakajima fighter was the Ki-27, a much more traditional Japanese fighter, with manoeuvrability emphasised over speed, protection and firepower. This was followed by the Ki-43, the most common Japanese army fighter of the Second World War. This too was a manoeuvrable but lightly armed aircraft, and after a successful period after the Japanese entry into the war would prove to be vulnerable to more modern Allied fighters.Work on the Ki-44 began in 1938, at almost the same time as the Ki-43. The Japanese Army Air Force decided that it needed two types of fighters - the manoeuvrable dog-fighter for normal use and a defensive interceptor for use against high flying enemy bombers. As a result Nakajima were asked to design a fighter that could reach 13,120ft in 5 minutes, with a top speed of 373mph at that altitude, and armed with two 12.7mm and two 7.7mm machine guns.
The Nakajima design team, led by Toro Koyama, were faced with an immediate problem. None of the 'fighter' engines available in Japan provided enough power to achieve this level of performance, and so they decided to use the Nakajima Ha-41, a two-row 14-cylinder radial engine capable of providing 1,250hp. This was seen as a 'bomber' engine, and was used in Nakajima's own Ki-49 heavy bomber, but twin-row radials would go on to power some of the most successful American fighters of the war. The Ki-44 was a low-wing monoplane, with short stubby wings. The wings had a straight leading edge but a tapering trailing edge. The fuselage was circular near the engine but narrow and flat-sided near the tail, a design that helped to improve its stability in the air. The aircraft carried two guns in the wings and two in the upper fuselage.
The first prototype Ki-44 (serial number 4401) was completed in the summer of 1940, and was rather heavier than expected. The new aircraft handled well, but its performance was not quite good enough. A series of modifications were tried out on the three prototypes, and eventually a top speed of 389mph at 13,120ft was achieved (although with all guns removed). With the guns installed the aircraft was expected to reach 360mph, and the new design was accepted by the Japanese army. Compared to the Ki-43 the new aircraft was heavier, slightly shorter and had a 4ft narrower wingspan. As a result the Ki-44 had a higher wing loading than the Ki-43, and was thus less manoeuvrable, but its top speed and rate of climb were both better. The Ki-44 entered production as the Army Type 2 Single-Seat Fighter Model 1, and a total of 1,225 were built by the time production ended late in 1944.
More info:
Pacific Wrecks - Nakajima Ki-44 Tojo