06/30/2012. Remarks by Johan Visschedijk: "The Hayabusa (Peregrine Falcon) was numerically the most important IJAAF fighter of the war. Despite the fact that, on December 8, 1941, the IJAAF possessed only forty Hayabusa fighters, this warplane appeared in rapid succession over Malaya, Burma, Sumatra and Java during the first six months of the Pacific conflict (receiving the Allied Air Forces code name "Oscar") and although obsolescent continued in production until Japan's final defeat.
The Nakajima Hikoki K.K. received a development contract in 1938 for a new single-seat fighter to which was allocated the designation Ki-43. Designed by Hideo Itokawa, the Ki-43 single-seat interceptor fighter and fighter-bomber was powered by the new Nakajima Ha.25 Sakae, and the first of three prototypes was completed in January 1939 at Nakajima's Ota factory.
The prototypes carried an armament of two 0.303 in (7.7 mm) Type 89 machineguns and attained a maximum speed of 323 mph (520 kmh). By comparison with the earlier Nakajima Ki.27, IJAAF pilots found the Ki-43 prototypes to be sluggish on the controls and to possess poor maneuverability.
Major redesign was therefore undertaken by Nakajima in order to reduce the fighter's weight and improve its characteristics. The wing area was slightly increased and one prototype was fitted with a fixed undercarriage, the weight of the retraction mechanism being considered a dispensable luxury by many at this time. The most important change was the introduction of the so-called "combat" or "battle" flap which, extended in action, provided additional lift, increased the turn rate and improved control response.
By means of this innovation, the Ki-43 became one of the most maneuverable fighters extant. All controls were extremely sensitive and the fighter was completely devoid of any vicious characteristics. Ten modified machines were built, the first of these being completed in November 1939, and IJAAF pilots were now highly enthusiastic about the new fighter.
Production of the fighter began at Nakajima's Ota factory, the first model being the Type I Fighter Model 1A (Ki-43-Ia) powered by the Ha.25 (later known as the Ha.35/12 under the unified IJAAF/IJNAF designation system) rated at 975. Armament comprised two 0.303 in (7.7 mm) machineguns, and performance included a maximum speed of 304 mph (489 kmh) at 13,123 ft (4,000 m) and a cruising speed of 199 mph (320 kmh) at 8,202 ft (2,500 m).
Production of the Ki-43-Ia began in March 1941, and this model was quickly supplanted by the Model 1B (Ki-43-Ib) which carried one 0.303 in (7.7 mm) gun and one 0.50 in (12.7 mm) gun, and the Model 1C (Ki-43-Ic) armed with two 0.50 in (12.7 mm) guns, the last-mentioned version being the first large-scale production model and assigned the popular name of Hayabusa.
Although the Ki-43-I Hayabusa enjoyed considerable success during the early months of the Pacific War, it soon became obvious that more power and increased armor protection were necessary. A rudimentary form of self-sealing fuel tank was introduced, 0.511 in (13 mm) armored head and back plates were installed in the cockpit, and an improved version of the Ha.25 engine, the Ha.115, was fitted, this being rated at 1,105 hp for takeoff and possessing a military rating of 1,085 hp at 9,186 ft (2,800 m).
Five prototypes were built embodying these modifications, the first of these being completed in February 1942, and as the Type 1 Fighter Model 2A (Ki-43-IIa) it entered prorluction at Ota, the earlier model being phased out, the 716th and last Ki-43-I Hayabusa being delivered during the February of 1943. The wing span of the Ki-43-IIa was reduced, armament comprised two 0.50 in (12.7 mm) guns, and underwing racks were fitted for two 551 lb (250 kg) bombs.
The Ki-43-IIa was also placed in production by the Tachikawa Hikoki K.K. in May 1943, and prior to this the 1st Army Air Arseral (Tachikawa Dai-ichi Rikugun Kokusho) began to build the type. In the event, the Arsenal suffered a number of difficulties, and by the time the program was abandoned in November 1943, only 49 Hayabusa fighters had been completed. Minor equipment changes distinguished the Ki-43-IIb, but further combat experience dictated a number of other changes in the Hayabusa, and between June and August 1942 three prototypes of the Ki-43-II-KAI were completed.
This model featured clipped wing-tips which reduced overall span, and entered service in the summer of 1943, serving over every theatre to which the IJAAF was committed. The Ki-43-II-KAI was capable of out-maneuvering every Allied fighter it encountered and its element was dog-fighting, but the P-38 Lightning, the P-47 Thunderbolt and the P-51 Mustang could all out-dive and out-zoom the Japanese fighter which could not withstand the greater firepower of the Allied types, frequently disintegrating in the air when hit.
Despite the obsolescence of the basic design development continued, and in December 1944 production of the Type I Fighter Model 3A (Ki-43-IIIa) was begun by both Nakajima and Tachikawa. This model switched to the Nakajima Ha.115-II Sakae engine rated at 1,250 hp and employing individual exhaust stacks to provide a certain amount of exhaust thrust augmentation. Maximum speed was boosted to 342 mph at 19,193 ft (5,850 m), and the Ki-43-IIIa was assigned to IJAAF interceptor units defending Tokyo and other major Japanese cities.
The ultimate development was the Model 3B (Ki-43-IIIb) developed by Tachikawa. This was the first model of the Hayabusa to mount large-caliber armament, two 0.787 in (20 mm) cannon supplanting the twin 0.50 in (12.7 mm) guns. The exhaust system was extensively modified and numerous changes were made to the fuselage and wings, but only two prototypes had been completed when the end of the war terminated further development. When Hayabusa production finished 5,878 machines had been delivered, 49 of these having been built by the 1st Arsenal and 2,629 by Tachikawa.
Entering service in January 1943, the pictured aircraft was part of the 1st and 11th Sentai, and first operated from Truk in Micronesia, later from Rabaul, Papua New Guinea, the aircraft was severely damaged on its final landing 4 mls (6 km) from Vunakanau airfield, Rabaul. After hostilities ended, Japanese servicemen repaired the aircraft, using parts from other Ki-43s and the aircraft was shipped to Australia for the Australian War Memorial. In 1954 it was sold and came on the New Zealand register as ZK-OSC, presently it is with the Flying Heritage Collection, registered as N750N."