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Ki-43 of the 64th Sentai
Nakajima Ki-43 "Hayabusa" of the 64th Sentai

Joe Baugher's Hayabusa files

Part one: Ki-43-I

The Nakajima Ki-43 Hayabusa (Peregrine Falcon) was numerically the most important fighter used by the Japanese Army Air Force during the Pacific War. It remained in production from the beginning of the Pacific War until its end in August of 1945. In many ways, it was a transitional type, bridging the gap between the lightly-loaded fighter monoplanes of the late 1930s with their fixed undercarriages and open cockpits and the higher-powered heavy fighters of the early 1940s with their retractable undercarriages and enclosed cockpits. Its appearance was a complete surprise to the Allies, and the fighter proved to be superior in performance to most of its opponents during the first year of the Pacific War. Most of the Japanese Army's aces established the larger part of their scores while flying this airplane. The Ki-43 is often confused with its contemporary, the famed Mitsubishi A6M Reisen (Zero Fighter) of the Japanese Navy, and was often misidentified as a "Zero" early in the war.

The Nakajima Hikoki K.K., located in the city of Ota in the Gumma Prefecture about 50 miles northwest of Tokyo, had been one of Japan's oldest and most prominent aircraft manufactures, and had been responsible for the design and manufacture of the Army Type 97 Fighter (Ki-27, later known to the Allies under the code name *Nate*), which was the first indigenous Japanese fighter to compare favorably with foreign fighters. Work on its successor began almost as soon as the Ki-27 had entered surface with the JAAF. For this project, the Army abandoned its long-standing policy of holding competitive fly-offs and gave Nakajima the contract to design a successor to the Ki-27. The specification called for a maximum speed of 311 mph, a climb rate of 5 minutes to 16,405 feet, a range of 500 miles, an armament of two 7.7-mm machine guns, and a maneuverability at least the equal of that of the Ki-27. The project was allocated the Kitai number Ki-43.

The design team was lead by Hideo Itokawa, who had also been the designer of the earlier Ki-27. The team came up with an aircraft that had the same general configuration as that of the Ki-27 and bore an obvious family resemblance. It was of low-wing configuration, with all-metal construction but with fabric-covered control surfaces. The three-spar wing was built in a single piece and had substantial area to keep loadings small for maximum maneuverability. The fuselage was exceptionally slim, and was covered by a metal stressed-skin. The aircraft differed from the Ki-27 in being fitted with a fully-enclosed cockpit for the pilot. The aircraft also differed from the Ki-27 in being fitted with a fully-retractable undercarriage, the main members retracting inwards into wells underneath the forward fuselage.

The prototype was completed at Nakajima's Ota plant and flew for the first time in January of 1939. Three prototypes were built, all of which were powered by the 925 hp Nakajima Ha-25 twin-row fourteen-cylinder air-cooled radial with single-speed supercharger. This engine was the Najakima-built counterpart of the Sakae (Prosperity) engine which powered the Mitsubishi A6M series. It was armed with two 7.7-mm Type 89 machine guns mounted in the upper engine cowling and synchronized to fire through the propeller arc. These aircraft did not have any engine cowling gills and had metal panels in the rear of the cockpit hood. A radio antenna mast was mounted on the cockpit hood and a telescopic gunsight protruded through the windshield.

Although the Ki-43 prototype met the Japanese Army's performance specifications, Army pilots were not happy about the maneuverability, which was not as good as that of the Ki-27. They regarded the retractable undercarriage as a frill which added only weight and reduced the maneuverability of the aircraft. In addition, they did not like the enclosed cockpit, which severely restricted vision to the rear. For a while, the future of the Ki-43 was in doubt.

The JAAF decided to conduct further tests and ordered ten service trial aircraft (Ki-43-KAI) from Nakajima. These ten planes were built between November 1939 and September 1940. They were all identical to the prototypes except for minor equipment changes and the fitting of a new all-round vision canopy that replaced the heavily-framed canopy of the prototypes which severely restricted pilot vision, especially to the rear. The second service trials machine was fitted with an experimental Nakajima Ha-105 engine equipped with a two-speed supercharger. Another service test machine carried a pair of 12.7-mm Ho-103 machine guns. Another one of the service trials aircraft had an alclad-treated duralumin outer skin, cowling gills, and a radio mast mounted on the starboard side of the fuselage. It was powered by a Ha-105 engine and was armed with two 12.7-mm Ho-103 machine guns. It had a new fuselage of smaller diameter and redesigned tail surfaces and wings.

Some authors report that one of the Ki-43 service trial aircraft was experimentally fitted with a fixed undercarriage, but this report appears to be in error.

One of the service trials aircraft was fitted with combat flaps which could be extended during flight to provide greater lift and to make it possible to maintain a much tighter turning circle. This modification was sufficiently successful that service pilots now commented favorably on the maneuverability. The aircraft was completely devoid of any vicious flying characteristics, and all controls were extremely sensitive.

The Koku Hombu agreed that the use of the combat flaps sufficiently improved the maneuverability to justify the issuance of a production order. The production version was to have an airframe similar to that of the last service trials machine, but was to be powered by a production version of the Najajima Ha-25 950 hp radial.

The initial production version was designated Army Type 1 Fighter Model 1A and was named Hayabusa (Peregrine Falcon). The Ki-43-1a entered production in April of 1941. It was powered by a Ha-25 Type 99 engine rated at 980 hp for takeoff. This engine was later known as the Ha-35/12 under the unified JAAF/JNAF designation system. The Ki-43-1a was initially fitted with a fixed-pitch, two-bladed wooden propeller which was soon replaced with a two-pitch metal unit. The armament consisted of two 7.7-mm Type 89 machine guns mounted in the upper cowling and synchronized to fire through the propeller arc. There were two attachment points for fuel tanks underneath the wing center section.

The first Ki-43-Ia fighters were delivered to the 59th and 64th Sentais in October of 1941, only eight months after production had begun at Ota. They were transferred to China shortly before the war with America broke out.

The next version was the Ki-43-Ib which differed from the Ia in having a heavier armament in which one of the Type 89 machine guns was replaced by a 12.7-mm Type 1 (Ho-103) machine gun. The Ki-43-Ic which followed it had two 12.7-mm Type 1 machine guns, and was the major production variant of the Model 1 series.

A total of 716 Ki-43-I production aircraft were built between April of 1941 and February of 1943.

When war in the Pacific broke out, only 40 Hayabusas had been delivered to combat units, and these were immediately taken to the Malay Peninsula by the 59th and 64th Fighter Groups. The initial combat missions consisted of escorts of Army Type 97 (Mitsubishi Ki-21) bombers in attacks on Hong Kong and Burma. First to face the Hayabusa were the P-40s of the American Volunteer Group and the Brewster Buffaloes of No 67 Fighter Squadron of the Royal Air Force. Japanese military security was sufficiently effective in maintaining a cloak of secrecy over the Type 1 Fighter that its appearance was a complete surprise to the Allies. Early war operations established the Ki-43 as one of the most feared Japanese fighters. Its performance was generally superior to that of most Allied fighters during the first year of the Pacific War. Nevertheless, its Navy contemporary, the Mitsubishi A6M Reisen (Zero Fighter), got more publicity back home in Japan, and the Japanese Army decided to reveal the existence of the Ki-43 to the Japanese public in April of 1942 so that it could get its fair share of recognition.

As compared to the Mitsubishi A6M2 Reisen, the Ki-43-Ic had a substantially lower wing loading but was nevertheless slightly inferior to the carrier-based fighter in overall maneuverability. The A6M2 was superior to the Ki-43-Ic in zoom climbing speed, although the Ki-43-Ic had a slight edge over the A6M2 in steady climbing rate to 16,400 feet. The primary weakness of the Ki-43-Ic was its light armament and its lack of armor protection for the pilot or for the fuel tanks.

Under the Allied system of assigning code names to Japanese aircraft, the Ki-43 was assigned the code name *OSCAR* in the Southwest Pacific theatre. At the same time, the the name *JIM* was assigned in the CBI theatre to what was thought at the time to be a retractable-undercarriage derivative of the Ki-27. It turned out that *JIM* and *OSCAR* were actually the same aircraft, and the name *OSCAR* was finally retained.

As the Ki-43-I was superseded by later, more powerful variants, it was reassigned to advanced fighter training schools. Others were delivered to the Royal Thai Air Force, which was then allied to Japan. These remained in service in Thailand until 1949.

Specification of Ki-43-Ia:

One Army Type 99 (Nakajima Ha-25) fourteen cylinder air-cooled radial rated at 980 hp for takeoff and 970 hp at 11,555 feet driving a two-bladed propeller.
Performance: Maximum speed 308 mph at 13,125 feet, climb to 16,405 feet in 5 minutes 30 seconds. Service ceiling 38,500 feet. Maximum range 745 miles.
Weights: 3483 pounds empty, 4515 pounds loaded, 5695 pounds maximum.
Dimensions: wingspan 37 feet 6 5/16 inches, length 38 feet 11 3/4 inches, height 10 feet 8 3/4 inches, wing area 236.81 square feet.
Armament: Two 7.7 mm Type 89 machine guns in the engine cowling. Two 33-pound bombs could be carried underwing. Two 44-imp-gall drop tanks could be carried.

continued in part 2