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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.

John Boyd's Aerial Attack Study

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.

Cowboy: interpreter, warlord, one more casualty

Part two: Ki-43-II

In pursuit of better performance, five Ki-43-I airframes were modified in February of 1942 to be powered by the 1150-hp Type 1 engine (which was the Nakajima Ha-115, a development of the earlier Ha-25). This engine had a two-speed supercharger and drove a three-bladed constant-speed metal propeller. The supercharger air intake was moved from underneath the cowling to its upper lip, with the carburetor intake remaining underneath the cowling. The wingspan was decreased by two feet and the wing area by 6.46 square feet to improve speed at low and medium altitudes. The windshield and cockpit canopy were raised slightly and a new reflector gunsight was fitted. The wing attachment points were strengthened to carry 551-pound bombs. In response to complaints from the field that the Hayabusa was too vulnerable to superficial combat damage, some rudimentary armor protection was provided for the pilot and self-sealing tanks were installed in the wings.

The improved Hayabusa model entered production as the Army Type 1 Fighter Model 2A (Ki-43-IIa). As the Model 2A entered production, the earlier Model 1 was progressively phased out, until the 716th and last Model 1 left the line in February 1943.

The carburetor air intake was deepened early in the production life of the Ki-43-IIa. The major production version of the Hayabusa was the Ki-43-IIb, which differed from the IIa only in minor equipment changes. The oil cooler, which had been mounted in a ring inside the cowling ahead of the engine and around the propeller shaft, was replaced by a honeycomb unit mounted inside a still deeper carburetor intake. Late production IIbs had their underwing bomb attachment points moved outboard of the main undercarriage legs to prevent bombs from hitting the propeller during dive bombing attacks at steep angles. Later production IIb aircraft had the oil cooler moved backward from the carburetor air intake and relocated underneath the central fuselage.

The modifications progressively introduced during the Ki-43-IIb production run were standardized on the Ki-43-KAI. This aircraft was also fitted with individual exhaust stacks that replaced the exhaust collector ring of earlier versions, and provided some amount of residual thrust augmentation. This variant also saw the underwing attachment points moved outboard of the landing gear. Three prototypes were built between June and August of 1942, and the Ki-43-KAI entered service in the summer of 1943. Some sources refer to this variant as the Ki-43-IIc, although this may be a "retrospective" designation introduced after the fact by Western sources for clarity.

The Ki-43-II-KAI was capable of out-maneuvering every Allied fighter it encountered, but the P-38, P-47, and P-51 could all out-dive and out-zoom the Japanese fighter.

Two additional production facilities, the Tachikawa Dai-Ichi Rikugun Kokusho (First Army Air Arsenal) and the Tachikawa Hikoki K.K. (Tachikawa Aeroplane Company, Ltd), were given contracts to manufacture the Ki-43 under license. The Tachikawa Dai-Ichi Rikugun Kokusho began production of the Hayabusa from Nakajima-supplied components in October of 1942. Unfortunately, the Army Air Arsenal did not have the experience needed for the manufacture of modern fighter aircraft, and was ordered to cease production in November 1943 after the delivery of only 49 Ki-43-IIa fighters. The Tachikawa Hikoki K.K. contractor was more successful, and built 2629 Ki-43-II and Ki-43-III Hayabusas beginning in May of 1943, and ceasing only with the end of the Pacific War in August 1945.

A total of 2500 Ki-43-IIs were built by the Nakajima parent plant at Ota.

In September 1943, the Allies were able to rebuild a complete fighter out of several wrecked Model 2A Hayabusas found at Lae, New Guinea. This aircraft was flown in mock combat against several different Allied fighters. Allied pilots commented favorably on the Hayabusa's sensitive controls and extreme maneuverability. It had no vicious flight characteristics, and its turning and stall characteristics were better than those of any Allied fighter. It handled well in the air, and had phenomenal low-speed handling capabilities which were aided by its set of combat flaps. It had excellent low-speed acceleration and could leap from 150 mph to 250 mph with extreme rapidity. Nevertheless, the Allied pilots felt that the Ki-43 was outclassed by the P-47 Thunderbolt, the P-38 Lightning, the Supermarine Spitfire, and even by later models of the P-40 Warhawk. The Hayabusa was appreciably slower than most Allied fighters and could usually be evaded by diving. The Hayabusa lacked effective firepower and its lack of effective armor protection made it vulnerable to superficial combat damage and often disintegrated in the air when hit. Nevertheless, Allied fighter pilots were always well-advised to avoid combat with the Hayabusa at low speeds since its rapid acceleration and excellent low-speed maneuverability made it a deadly opponent in such situations.

Specification of Ki-43-IIb:

One Army Type 1 (Nakajima Ha-115) fourteen cylinder air-cooled radial rated at 1150 hp for takeoff and 980 hp at 18,375 feet driving a three-bladed propeller.
Performance: Maximum speed 329 mph at 13,125 feet, climb to 16,405 feet in 5 minutes 49 seconds. Service ceiling 36,750 feet. Normal range 1095 miles. Maximum range 1990 miles.
Weights: 4211 pounds empty, 5710 pounds loaded, 6450 pounds maximum.
Dimensions: wingspan 35 feet 6 3/4 inches, length 29 feet 3 5/16 inches, height 10 feet 8 3/4 inches, wing area 230.34 square feet.
Armament: Two 12.7-mm Type 1 machine guns in the engine cowling. Two 66-pound or 551-pound bombs could be carried underwing. Two 44-imp-gall drop tanks could be carried.

Part three: Ki-43-III

Despite the obsolescence of the basic design, developmental work on the Hayabusa continued until the end of the Pacific War.

The Ki-43-IIIa was the last Hayabusa variant. Ten prototypes were built starting in May of 1944. It was similar in airframe and armament to the Ki-43 KAI, but was powered by a Najajima Ha-115-II Sakae air-cooled radial rated at 1230 hp at 9185 feet. This engine employed individual exhaust stacks to provide a certain amount of exhaust thrust augmentation. Production began in December of 1944, most of the aircraft being built by Tachikawa Hikoki K.K..

The Ki-43-IIIa was assigned to units defending Tokyo and other major Japanese cities and was also used in numerous suicide attacks during the final phases of the Pacific War.

Tachikawa also built two prototypes of the Ki-43-IIIb, which was a specialized interceptor version powered by a 1250 hp Mitsubishi (Ha-33) 42 (Ha-112) fourteen-cylinder air cooled radial. The pair of 12-7-mm machine guns (which had remained the standard Hayabusa armament since the Ki-43-Ic) were replaced by two 20-mm Ho-5 cannon, which made the Ki-43-IIIb the first Hayabusa variant to carry large-caliber armament. Further changes were made to the fuselage and wing structure as well as further modifications to the exhaust system. Overall wing span was similar to that of the Model IIIa, at 35 feet 6 3/4 inches. This version was under test when the war in the Pacific ended and brought further work to a standstill.

After the war, a few Hayabusas left in the East Indies by the withdrawing Japanese forces were salvaged by the Indonesian People's Security Force and used in 1946 in fighting against the Dutch. A few Hayabusas were confiscated by the French upon their return to Indo-China and were flown by pilots of the French Groupes de Chasse I/7 and II/7 against insurgents. These were replaced by Spitfire IXs shipped from France.

The only known surviving Ki-43 is a Model 2 (-IIa) that was on display at Clark AFB in the Philippines. With the departure of the Americans from Clark, I am not sure that this plane is still there.

Specification of Ki-43-IIIa:

One Army Type 1 (Nakajima Ha-115-II) fourteen cylinder air-cooled radial rated at 1300 hp for takeoff and 1230 hp at 9185 feet driving a three-bladed propeller.
Performance: Maximum speed 358 mph at 21,920 feet. Climb to 16,405 feet in 5 minutes 19 seconds. Service ceiling 37,400 feet. Normal range 1320 miles. Maximum range 1990 miles.
Weights: 4233 pounds empty, 5644 pounds loaded, 6746 pounds maximum.
Dimensions: wingspan 35 feet 6 3/4 inches, length 29 feet 3 5/16 inches, height 10 feet 8 3/4 inches, wing area 230.34 square feet.
Armament: Two 12.7-mm Type 1 machine guns in the engine cowling. Two 66-pound or 551-pound bombs could be carried underwing. Two 44-imp-gall drop tanks could be carried.

Sources:

Famous Fighters of the Second World War, Second Series, William Green, Doubleday 1967.

The Nakajima Ki.43 Hayabusa, Martin C. Windrow and R. F. Francillon, Aircraft in Profile, Doubleday, 1969.

Warplanes of the Second World War, Fighters, Volume 3, William Green, Doubleday, 1964.

Japanese Aircraft of the Pacific War, Rene J. Francillon, Naval Institute Press, 1979.

Tales of the Flying Tigers

To which the webmaster adds the following:

The Ki-43 was developed before the Navy's Zero, but proved too sluggish in combat trials. The enclosed cockpit could not have been seen as a drawback, as Joe suggests, because the front-line army fighter (Nakajima Ki-27 "Nate") had just such a cockpit. All three fighters--Ki-27, Ki-43, and A6M--had bubble-type canopies and excellent rear version as compared to western fighters of the time. Because of its maneuverability problems, however, the Ki-43 was shelved and its engine was used for the Zero instead.

When Japan decided to prepare for war in Southeast Asia, the army needed a fighter that could fly 400 miles, fight, and go home, a capability utterly beyond the fixed-gear Ki-27 "Nate." The army's leading fighter pilot and group commander, Kato Tateo, was brought in to save the Hayabusa. It was evidently his idea to add butterfly combat flaps, which actually enabled the Hayabusa to turn inside a Zero. The Hayabusas that Kato commanded in the 64th Sentai, and I think also those in the 59th Sentai, were actually pre-production models. It was the late start, and especially the fact that it never saw service over China, that caused the Hayabusa to be unknown to western air forces. The British in Malaya identified it as a Zero, and so did the AVG Flying Tigers in Burma. However, British intelligence officers in Rangoon correctly determined that it was a Model "01" from Nakajima, though failing to realize how different it was from the fixed- gear model did most of the fighting in Southeast Asia. (Type One Army Fighter was the Hayabusa's shorthand identification, based on its its year of introduction, just as the A6M was the Type Zero Carrier Fighter.)

The great weakness of the early Hayabusa was how its wings were joined to the fuselage. (The plane was built with its engine compartment, cockpit area, and wings as a unit, with the tail attached to that.) At least one plane shed its wings in combat over Malaya, and another pilot was killed on 25 Dec 1941 when he collided with a Tomahawk flown by Parker Dupouy. (Don Lopez of NASM is another American pilot who collided with a Hayabusa and lived to tell about it.)

There is some confusion as to whether the early-model Hayabusas had two 7.7mm guns, or one 7.7 and one 12.7mm. In any event, when the 64th Sentai was reequipped with Ki-43-II models in April 1942, both nose guns were large-caliber. However, the rate of fire was so slow that many or most pilots had one gun taken out and replaced with a faster-firing 7.7mm. These were the models that fought the AVG on 28 April 1942 near Lashio, Burma.

A fascinating sidelight of the Hayabusas of 1941-42 was that they still relied on hand signals and other visual cues. They had radios as original equipment, but these never worked air-to-air, even after the pilots tried suspending them in a sort of hammock to protect them from vibration.

At least 7 Hayabusas still exist, including 4 incomplete models at the Australian War Memorial in Canberra and 1 in somewhat better shape in Scone NSW Australia. There is an apparently fine model at the Museum Pusat Tni-Au in Indonesia, and a beauty at Oskkosh WI that actually belongs to NASM.

In addition to the books Joe Baugher cited, see the following:

Nakajima Ki.43 Hayabusa I-III, by Richard Bueschel (Arco, 1970; Schiffer, 1995).

Flying Tigers: Claire Chennault and the American Volunteer Group, by Daniel Ford (Smithsonian Institution Press 1991). A lot of stuff here from the Japanese, not otherwise available in English, even if I do say so myself.

Broken Wings of the Samurai: The Destruction of the Japanese Airforce, by Robert Mikesh (Naval Institute Press 1993). The Oshkosh Hayabusa is pictured here.

Two good first-person accounts in Japanese are Tusbasa no Kessen and Hayabusa Sentotai cho Kato, both by the sergeant-pilot Hinoki Yohei (Kojinsha 1984 and 1987). And two movies, interesting even to those of us who don't know the language: Aa Hayabusa Sentotai cho Kato, a 1943 propaganda film about the 64th Sentai; and Aa Hayabusa, a documentary made in the 1980s and featuring Sergeant Hinoki himself, both produced by Toho and available on videotape.

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