Nakajima Ki-43 Hayabusa (Peregrine Falcon) 'Oscar' (Army Type 1 Fighter)

The Nakajima Ki-43 Hayabusa (Peregrine Falcon) was the most numerous Japanese Army Air Force fighter aircraft of the Second World War. At the start of the Pacific War it swept aside the outclassed Allied aircraft posted in the Far East, but as the war continued the Ki-43 was outclassed by faster and more heavily armed Allied aircraft, and large numbers were lost on every front where it fought.


Work on the Ki-43 began in December 1937. Earlier Japanese Army fighters had emerged from a competitive tendering process, with a number of aircraft manufacturers requested to submit designs. With the Ki-43 the Army abandoned that approach, and instead contacted Nakajima directly and asked them to design a new fighter to replace their own Nakajima Ki-27 (Army Type 97 Fighter). The new fighter was to have a top speed of 311mph, to be able to climb to 16,405ft in five minutes, have a range of 500 miles, be armed with two 7.7mm machine guns and be as manoeuvrable as the Ki-27. 

Plans of Nakajima Ki-43 'Oscar
Plans of
Nakajima Ki-43 'Oscar'

The first prototype of the Ki-43 (serial number 4301) was completed on 12 December 1938 and made its maiden flight in January 1939. It was immediately clear that the new aircraft did not live up to expectations. It was simply not manoeuvrable enough for the Japanese Army pilots, who reported that it was unresponsive to control, stiff, slow and too heavy. The cockpit canopy was awkward and the landing gear difficult to use. Two similar prototypes followed (No.4302 in February 1939 and No.4303 in March 1939), but there were no significant improvements, and the Army rejected the Ki-43. 

Undaunted Nakajima began work on the first of a series of ten development aircraft (No.4304 to 4313) that saw the Ki-43 turn into an excellent design. A series of changes were introduced during this process. Aircraft 4305 and 4313 were powered by the Ha-105 radial engine. No.4310 was armed with two 12.7mm machine guns. No.4312 was given a treated duralumin outer skin, cowling gills and a radio mast. The most important innovation was the introduction of 'butterfly' flaps on No.4311, greatly improving the aircraft's manoeuvrability. Finally No.4313, the tenth pre-production machine, combined the features of Nos.4309 and 4310, and also had a smaller diameter fuselage, new tail surfaces and modified wings. It was also armed with two 12.7mm machine guns. Most of these features were retained in the first production aircraft, although the Ha-105 engine and 12.7mm guns were not included.

After examining the development aircraft the Army decided to order the aircraft into production. The Army Type 1 Fighter was to have the fuselage of the tenth pre-production aircraft, the Nakajima Ha-25 engine and to be armed with two 7.7mm machine guns. The aircraft would be produced at three factories. Nakajima produced the most aircraft, completed 3,239 of which 2,492 were Ki-43-IIs. The Army's First Army Air Arsenal (Tachikawa Dai-Ichi Rikugun Kokusho) was the least successful, producing 49 aircraft between October 1942 and November 1943. Finally the Tachikawa Hikoko K.K. (Tachikawa Aircraft Company) produced most later aircraft, completing 2,629 aircraft between May 1943 and the end of the war, with around 1,600 Ki-43-IIs and 1,000 Ki-43-IIIs. 


The Ki-43 was a standard low-wing cantilever monoplane, with a retractable undercarriage, enclosed cockpit and supercharged radial engines. The two guns were carried in the upper fuselage, firing through the propeller. The most important design feature of the Ki-43 was the butterfly flaps. These were wide chord flaps that could be used in combat to instantly increase the effective area of the wing. This increased the aircraft's handling, manoeuvrability and turning circle and made it a very dangerous opponent.


Ki-43-Ia (Army Type 1 Fighter Model 1A)

Drawings of Nakajima Ki-43 'Oscar
Drawings of Nakajima Ki-43 'Oscar'

The Ki-43-Ia was the first production version of the Hayabusa. It was armed with two 7.7mm machine guns and could carry two 33lb bombs under the wings. Only 34 were produced, all between April and June 1941.

Ki-43-Ib (Army Type 1 Fighter Model 1B)

The Ki-43-Ib was armed with one 7.7mm machine gun and one 12.7mm machine gun. Around 45 were produced between July and September 1941.

Ki-43-Ic (Army Type 1 Fighter Model 1C)

The Ki-43-Ic was the main production version of the -I. Just over 600 aircraft were produced between September 1941 and February 1943. The Ki-43-Ic was armed with two 12.7mm machine guns.


The Ki-43-II was the main production version of the aircraft, and included a number of significant improvements, including the use of a more powerful Ha-115 engine and the introduction of limited pilot armour and self-sealing fuel tanks. The Ha-115 engine was a more powerful development of the Ha-25, and included a two-stage supercharger. The first of five prototypes was completed in February 1942 (just as the Ki-43-I was at its most successful).  

Ki-43-IIa (Army Type 1 Fighter Model 2A)

The Ki-43-IIa was the first production version of the -II. The first production aircraft were completed by Nakajima in November 1942, and Nakajima continued to produce the -IIa until September 1944. The Army also attempted to built the -IIa at the Army Air Arsenal at Tachikawa, but this was a failure and only 49 aircraft were completed before production there ended in November 1943.

Nakajima Ki-43-II
Nakajima Ki-43-II

The -IIa was similar to the prototypes. It was armed with two 12.7mm machine guns and could carry two 551lb bombs under the wings. The wing span was reduced by 1ft 11 5/8in and the wing area was also reduced, improving the aircraft's speed at low and medium levels. 13mm of head and back armour was installed, along with self-sealing fuel tanks.

Ki-43-IIb (or II Otsu)

The Ki-43-IIb was produced by the Tachikawa Hikoki K.K. (Tachikawa Aircraft Company). It was similar to the Ki-43-IIa, but with minor equipment changes. The oil cooler was changed and the carburettor intake modified. During the production run the wing attachment points were moved further out to prevent incidents when the bombs hit the propeller when the aircraft acted as a dive bomber.

Ki-43-II KAI

The Ki-43-II Kai combined all of the modifications introduced on the IIa and IIb, and also had a new exhaust system, with individual exhaust stacks that produced a limited amount of extra boost.

Ki-43-IIIa (Army Type 1 Fighter Model 3A)

The Ki-43-IIIa was powered by the 1,190hp Nakajima Ha-115-II engine, which could produce 1,230hp at 2,800m. It entered production in October 1944 at Tachikawa, and around 1,000 aircraft were completed before the end of the war.


Two prototypes were produced on the Ki-43-IIIb interceptor. They were powered by the Mitsubishi Ha-112 engine of 1,250hp and were armed with two 20mm cannon. The aircraft was intended for the defence of the Japanese Home Islands, but was still being tested when the war ended.  

Combat Record

The Ki-43 served with the Japanese Army Air Force in larger numbers than any other fighter, and was used on every front where the JAAF was engaged. The small numbers of -Ia and Ibs were used to equip the fighter schools, while the first -Ics went to the 59th and 64th Sentais. After training in Japan these two units moved to China with 40 aircraft between then, arriving just before the attack on Pearl Harbor of December 1941.

Nakajima Ki-43 attacking North American B-25 Mitchell
Nakajima Ki-43 attacking North American B-25 Mitchell

The Ki-43 first saw combat over Malaya and Burma, fighting alongside larger numbers of the Ki-27 'Nate'. The Allies were outnumbered and were operating a mix of less modern types (the defence of northern Malaya was entrusted to the Brewster Buffalo). The Ki-43 was able to out manoeuvre the Buffalos, Hurricanes and P-40s it came up against over Malaya and Burma, and the Japanese quickly swept the Allies from the skies. As larger numbers of Ki-43s became available the 1st, 50th and 77th Sentais also began to operate the type over Burma. In this area the Ki-43 was initially given the code-name 'Jim', and was believed to be a development of the earlier Ki-27 'Nate'.

The 11th Sentai converted to the Ki-43 in January 1942 and took part in the invasion of the invasion of the Dutch East Indies.

The 24th and 33rd Fighter Sentais and 13th Fighter-Attack Sentai received their Ki-43s in the spring of 1942 and operated in the New Guinea area.

In the Pacific theatre the aircraft was recognised as a new type and given the code-name 'Oscar'. When it was realised that 'Jim' and 'Oscar' were the same aircraft the Pacific code-name was retained.

In the first few months of the Pacific War the manoeuvrable Ki-43 was a deadly opponent (as was the Navy's Zero), but the Allies soon developed tactics that could be used successfully against it. The key to success was to avoid getting into a dog-fight and instead make a fast passing attack. This negated the Ki-43's manoeuvrability, and took advantage of its lack of pilot armour or self sealing fuel tanks.

The improved Ki-43-IIa, with limited armour, began to reach service units during the spring of 1943. The 1st, 13th, 24th, 26th and 33rd Sentais, in the New Guinea area, all had the new aircraft by the summer. The type also reached units in China and Japan. It was then superseded by the Ki-43-IIb, which reached every JAAF theatre, and by the Ki-43-II Kai.

By the time these improved models reached the front line the tide had turned against the Japanese, and the JAAF found itself on the defensive. The Ki-43 was too slow, too lightly armoured and under-gunned, while the Allies now had increasingly large numbers of heavier and better armed fighters. The JAAF began to suffer very heavy casualties on New Guinea and over Burma, a trend that continued as the front line was pushed back towards the Home Islands. Desperate attempts were made to defend New Guinea, but many of the Ki-43 units that were flown onto the island would never leave.

The Ki-43 was used in large numbers during the defence of the Philippines. At least seven sentais were transferred to the area from China, New Guinea, Burma and Thailand and another nine from Japan. Once again these units found themselves outnumbered and outgunned, and most suffered very heavy casualties before they were finally pulled out, while several units were destroyed.

One sentai took part in the defence of Iwo Jima, and six fought on Okinawa, where the Ki-43 began to be used in the kamikaze role. The Ki-43 was also used in large numbers during the defence of Japan, but its light armament meant that it was generally unsuccessful when attacking B-29s. The Ki-43 was also used in kamikaze attacks on targets close to Japan, and in the short campaign in Manchuria.

The K-43 was also used in small numbers by the Royal Thai Air Force. This began in the spring of 1944 when a number of ex-Japanese Army aircraft were transferred. The Thais were officially allies of the Japanese, but the air force was seen as largely pro-Allies, and the units posted in the Bangkok area saw very little combat. The Thai Ki-43s remained in use until the late 1940s.

Post War

The Ki-43 was used by the Indonesian People's Security Force during their campaign against the Dutch, who were attempting to return to the East Indies. The Ki-43 was also used for a short time by the French, who found themselves short of aircraft to deal with the Communists in Indo-China. Groupes de Chasses I/7 and II/7 made use of former Japanese aircraft for a short period before more modern American aircraft arrived.

Ki-43-IIb (short)
Engine: Nakajima Ha-115 radial engine
Power: 1,150hp
Crew: 1
Wing span: 35ft 6.75in
Length: 29ft 3.25in
Height: 10ft 8.75in
Empty Weight: 4,211lb
Maximum take-off Weight: 5,710lb
Max Speed: 329mph at 13,125ft
Cruising Speed:
Service Ceiling: 36,725ft
Range: 1,988 miles
Armament: Two 12.55mm forward firing machine guns
Bomb-load: Two 551lb bombs under the wings

Japanese Aircraft of World War II 1937-1945, Thomas Newdick. A useful shorter reference work looking at the combat aircraft fielded by the Japanese during the Second World War, along with those jet and rocket powered aircraft that got closest to being completed. A useful guide to the aircraft of the Japanese Army and Navy, a key element in the rapid expansion of Japanese power, and in the increasingly desperate defence of their expanded Empire as the war turned against them. Organised by type of aircraft, with enough information on each type for the general reader, and longer sections on key aircraft such as the Zero (Read Full Review)
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How to cite this article: Rickard, J (8 June 2011), Nakajima Ki-43 Hayabusa (Peregrine Falcon) 'Oscar' (Army Type 1 Fighter),

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