The Nakajima Ki-27 'Nate' was the first monoplane fighter to enter service with the Japanese Army Air Force, and was still numerically the most important fighter in Army service in December 1941.
During the 1920s and 1930s the Japanese Army used a series of competitions to decide which aircraft to order. Kawasaki and Nakajima were the main competitors in the fighter contests. Nakajima dominated at first, with the Type A-4 Kosen and Type 91 Fighter, but Kawasaki then took over, winning two fighter contests in a row with the KDA-5 Type 92 and Ki-10 Type 95 biplane fighters. Mitsubishi also entered most of these design contests, but without success.
In June 1935 the Japanese Army issued the specifications for a new generation of fighter aircraft. Nakajima, Kawasaki and Mitsubishi were each asked to submit two prototypes of a fighter aircraft with equal or better performance than any fighter known to be under development overseas.
In the aftermath of its failure in the Type 95 fighter contest Nakajima decided to set up separate design teams for Navy and Army projects, appointing Dr. Hideo Itokawa to head the Army team. They also decided to work on a private-venture monoplane fighter, the Type P.E. (Pursuit Experimental).
This decision gave Nakajima a head start in June 1935, and theirs was the first design to be submitted to the Army, where it was given the designation Ki-27. Kawasaki responded next, with the Ki-28, while Mitsubishi was last to submit the design for the Ki-33, a modified version of the A5M2.
The Nakajima Type P.E. was generally forward looking design, although with some increasingly out-dated features. It was a low-wing cantilever monoplane, with an open cockpit (on production aircraft a closed canopy was provided, but many pilots flew with it open). It had a fixed undercarriage, and carried two 7.7mm machine guns, the standard fighter armament until the mid 1930s, but much more heavily armed aircraft were under development elsewhere in the world. The Type P.E. and the prototype Ki-27s were powered by the 650hp Nakajima Ha-1a, and the production versions would use a similar engine, leaving the Ki-27 somewhat underpowered compared to the 1,000hp fighters being developed in the west. Finally the aircraft had a fixed, spatted undercarriage.
The single Type P.E. was completed in July 1936, and was followed in October by the first prototype Ki-27. This aircraft, Ki-2701, made its maiden flight on 15 October 1936, several months after the Mitsubishi Ki-33 prototype, but one month ahead of the Kawasaki Ki-28. The second Ki-27 prototype followed next, with a larger wing to improve manoeuvrability, and all three companies had completed both prototypes by the end of the year.
The competitive trials began early in 1937. The Ki-27 was slightly slower than its competitors, came second on climb rate, but won hands-down on manoeuvrability. The Kawasaki design was faster and had a better climb rate, but not by a big enough margin to make up for its poor manoeuvrability.
The Nakajima Ki-27 was the clear winner, and received the only order for pre-production aircraft. These ten machines, with enclosed cockpits and larger wings were completed between June and December 1937. On 28 December 1937 the Ki-27 was ordered into production as the Army Type 97 Fighter.
Kawasaki and Mitsubishi both complained about this result, arguing that Nakajima must have had advance notice of the contest. The two companies helped convince the Army not to hold any more open design contests, but instead to ask a single company to produce each future design. Kawasaki may have been hoping that they would be that company, but instead they handed dominance of Army fighter production to Nakajima, who were awarded the contracts to develop the Ki-43, Ki-44 and Ki-84.
Nakajima produced one Type P.E. and two Ki-27 prototypes in 1937 and ten pre-production aircraft between June and December 1937. Full production of the Ki-27a began at Ota in December 1937, and between then and 1942 Nakajima produced 2,005 of the Ki-27a and Ki-27b. They also produced two prototypes of the Ki-27 Kai in 1940.
Some sources suggest that the Mansyu Aircraft Company of Manchuria produced around 1,379 Ki-27s, but this is suspiciously similar to the number of Ki-79 trainers that they produced. The Ki-79 was directly based on the Ki-27, possibly explaining the confusion.
The Ki-27 entered front line service just as the JAAF was in the process of a major reorganisation. Until 1937 the Army Air Force had been organised into Air Regiments, each of which contained a mix of fighters, bombers, reconnaissance aircraft and transports. Combat experience in China suggested that this structure wasn't satisfactory. The Air Regiments were split up into Sentai, generally translated as squadrons or battalions. The fighter sentai were made up of three companies of 12 aircraft, making them almost the direct equivalent of a USAAF fighter group of three squadrons.
The Ki-27 entered service with the 59th Sentai, on 1 July 1938 at Kagamigahara, Japan. It was followed by the 77th Sentai at Nanking on 27 July and the 64th Sentai in Manchuria and the 33rd Sentai at Kyoju in China on 1 August, and by an increasingly large number of units after that.
In the late summer of 1938 the Ki-27 entered combat in northern and central China, where it soon helped the Japanese gain air superiority, defeated the Curtiss Hawk IIIs of the Chinese Air Force. The Ki-27 continued to control the skies into 1939.
The Ki-27 also saw combat against the Soviet Air Force. The first border clash came in the summer of 1938 and saw small scale losses and large scale claims on both sides. It was followed in May 1939 by a more serious conflict, on the border between Outer Mongolia and the Japanese puppet stake of Manchoukuo. The end result of the conflict was decided by the Soviet victory at Khalkin Gol (although a Soviet advance into Manchuria was less successful), but at the same time massive air battles developed. The Ki-27 proved to be greatly superior to the Polikarpov I-15bis biplane, although the I-153 with its retractable undercarriage caused some problems. The Polikarpov I-16 monoplane was a more serious threat, but the Japanese probably scored more victories than the Soviets even in these clashes. The fighting over Manchuria helped provide many of the most successful Japanese pilots of the Second World War with their first real combat experience. Both sides made wildly exaggerated claims during this conflict, with the Japanese claiming to have shot down 1,340 Soviet and Mongolian aircraft for the loss of only 120 of their own. The Soviets claimed that they had only deployed 450 aircraft to the area, and had achieved 215 victories.
Second World War
By December 1941 the Ki-27 was obsolescent by world standards, but it was still the most important fighter in Japanese Army service. A handful of Nakajima Ki-43s and Ki-44s had already reached the front, but the majority of the Japanese Army fighters that crushed the Allies in Malaya, Burma and the Philippines were the older Ki-27s.
At first the Ki-27 had two Allied code-names - 'Abdul' in the China-Burma-India theatre and 'Nate' in the south-west Pacific. After 1943 'Nate' was used almost exclusively.
Most Allied aircraft in the area were equally obsolescent - Malaya was defended by a force of Brewster Buffaloes, while the more modern P-40s in the Philippines were overwhelmed by superior numbers and many were destroyed on the ground.
Events in Burma were a little different. Here the Allies started with RAF Buffaloes and Curtiss P-40Cs of the American Volunteer Group. They were eventually joined by a small number of Hurricanes, but the Allies were outnumbered by at least five-to-one. Despite this the Allied pilots were able to more than hold their own against the Ki-27, which was soon found to be very vulnerable to battle damage. Once Allied pilots learnt to avoid dogfights the Japanese were in trouble, and at least 137 Japanese aircraft were destroyed. The Allies were less successful on the ground, and were forced to retreat from Rangoon all the way to the Indian border. Their resistance in the air came to an end after the Japanese managed to destroy most of the Allied aircraft on the ground at Magwe in late March.
The Ki-27 was phased out of front line service after the initial Japanese victories and was replaced by the Nakajima Ki-43, Nakajima Ki-44 and later the Kawasaki Ki-61. The large number of surviving Ki-27s were used as training aircraft, before returning to the front line late in the war when they became one of the most widely used kamikaze aircraft.
The Ki-27a had the larger wings of the pre-production aircraft, but the cockpit had a conventional windshield, replacing the original long streamlined version, and the rear part of the cockpit was metal covered. The Ki-27a was armed with two 7.7mm machine guns and powered by the Nakajima Ha-1b radial engine.
The Ki.27b entered production during 1939. It retained the same engine, wings and guns as the Ki-27a, but with a completely glazed cockpit.
The Ki-27 Kai was produced in 1940 when the new Ki-43 was not living up to expectation. It was a lighter, slightly faster version of the Ki-27, with a top speed of 295mph. Two were built in 1940, but the project was cancelled after the Ki-43 overcame its problems.
Engine: Nakajima Ha-1b (Army Type 97) nine-cylinder air-cooled radial
Power: 710hp at take-off, 780hp at 9,515ft
Wing span: 37ft 1 1/4in
Length: 24ft 8 7/16in
Height: 10ft 7 15/16in
Empty Weight: 2,447lb
Loaded Weight: 3,946lb
Max Speed: 292mph at 11,480ft
Cruising Speed: 217mph at 11,480ft
Range: 390 normal, 1,060 maximum
Armament: Two 7.7mm machine guns
Bomb-load: Four 55lb bombs or two 28.6 imperial gallon drop tanks