Emphasis up to 1939 had always been on manoeuvrability, but in that year a specifica¬tion was issued calling for a fighter which could reach 600 km/h (373 mph) at 4000 m (13100 ft), climbing to that height in no more than five minutes and armed with at least four machine guns. Nakujima’s design team, led by engineer Yasumi Koyama, had the first Ki 44 prototype in the air during August 1940.

Nakajima Ki-44 Shoki Article

A low wing all metal cantilever monoplane, it had a deep forward fuselage tapering sharply to the tailplane, which had the fin and rudder set further back than the horizontal tail surfaces. The wing was built in three sections, with a broad centre section integral with the fuse¬lage. The undercarriage retracted inwards and the tail wheel was fully retractable. Metal stressed skin covering was employed on fuselage and wings. The combat flap intro¬duced in the Ki 43 was used on all Ki 44s built. Power was provided by a 14 cylinder two row 1250 hp Nakajima Ha 41 radial engine. Test flights were successful, although the small wing resulted in a high wing loading and a high landing speed. The Ki-44 prototypes incorporated the manoeuvring flaps that had been introduced on the Ki-43, and carried an armament of two 7.7mm and two 12.7mm machine-guns.

The first prototype was soon followed by two more, but the top speed and rate of climb were not up to specification. The super¬charger intake and cowl flaps were revised several times and every effort was made to reduce drag. Maximum speed rose to 616 km/h (383 mph) in a prototype flown without armament by chief test pilot Hayashi.

Seven service test aircraft were built and issued in September 1941 to a special operational evaluation unit, the 47th Dokuritsu Chutai (independent squadron), which flew the Ki 44 Shoki (Dragon Slayer), against the Chinese over Canton. The Ki-44 was involved in a series of comparative trials against Kawasaki’s Ki-60 prototype, based on use of the Daimler-Benz DB 601 engine, and an imported Messerschmitt Bf 109E. The Ki 44 was accepted for service in September 1942 as the Army Type 2 Single seat Fighter, which carried the same armament as the prototypes.

A total of 40 Ki 44 Is were built, including small numbers of the Ki-44-Ib, and the similar KI-44-Ic with some minor refinements. Closely resembling the preproduction aircraft, but with armament increased from two fuselage mounted 7.7 mm (0.303 in) Type 89 machine-guns and two wing mounted 12.7 mm (0.5 in) Ho 103 machine guns to four 12.7 mm weapons.

Pre-production and early production air¬raft were designated Model 1. Model 2 prototype and preproduction aircraft (eight in all) were built and tested during summer and autumn 1942. Powered by the 1520 hp Nakajima Ha 109 radial, they had limited pilot armour and fuel tank protection. There was provision for two drop tanks each with 125 litres (27.5 Imp gal) of fuel. Only small numbers of the Ki- 44-IIa were built, the variant being followed by the major production Ki-44-IIb.

A number of the Ki 44 IIc version armed with four 20 mm (0.79 in) Ho 3 cannon in place of the 12.7 mm wing guns went into service later in the war. Only in late 1943 did Tojo (the Allied codename for the Ki 44) appear in quantity on the war fronts. Its impressive rate of dive and climb 5000 m (16 400 ft) was reached in just over four minutes made them especially suitable for target defence. The 85th and 87th Sentais for example, defended the strategically important oil refineries on Surnatra. Other Sentais were deployed in the Philip¬pines in a vain attempt to stem the US tide, or based at home where they had some success against Boeing B 29 Superfortress attacks.

The final variant, Ki 44 III had ejector ¬type thrust augmented exhaust stacks (fitted also to a few earlier machines) and was powered by a 1491kW / 2000 hp Nakajima Ha 145 18 ¬cylinder engine, an increased wing area and enlarged vertical tail surfaces. Armament was either four 20 mm Ho 5 cannon or two Ho 5s and two 37 mm (1.46 in) Ho 203s. Only evaluation aircraft were completed, and snags with the new engine caused development of the Ki 44¬-III to be abandoned.

When Japan surrendered, Ki 44s still equipped three Sentais and had established a fine reputation with pilots able to exploit their good qualities, while avoiding old style dogfights in which their inferior manoeuvra¬bility became apparent. Among a number of army air force aces who made their marks flying the Ki 44, perhaps the most outstand¬ing was Colonel Yukiyoshi Wakamatsu of the 85th Sentai. He had achieved at least 18 victories before he was shot down and killed in December 1944.

A total of 1225 aircraft, including prototypes, were built up to December 1944 when production was phased out in favour of the Ki 84.

Ki 44 I
Span: 9.45 m (31 ft)
Length: 8.75 m (28 ft 9 in)
Gross weight: 2550 kg (5622 lb)
Maxi¬mum speed: 580 km/h (360 mph).

Ki 44 II
Span: 9.45 m (31 ft)
Length: 8.78 m (28 ft 10 in)
Gross weight: 2764 kg (6093 lb)
Maxi¬mum speed: 605 km/h (376 mph).

Ki-44-IIb
Engine: 1 x Nakajima Ha-109 Type 2, 1133kW / 1520 hp
Max take-off weight: 2995 kg / 6603 lb
Empty weight: 2105 kg / 4641 lb
Wingspan: 9.45 m / 31 ft 0 in
Length: 8.8 m / 28 ft 10 in
Height: 3.25 m / 10 ft 8 in
Wing area: 15 sq.m / 161.46 sq ft
Max. speed: 605 km/h / 376 mph at 17,060 ft
Ceiling: 11200 m / 36750 ft
Range w/max.fuel: 1700 km / 1056 miles
Armament: 4 x 12.7mm machine-guns
Crew: 1

Design work began on the Ki-43 in late 1937 with the Army instructing Nakajima to supersede the Type 97 Fighter Ki-27. The specifications were precise and within one year the first prototype was complete. Departing from the previous practice of selecting a suitable design by calling for competitive projects from two or more air¬craft firms, the specification was issued only to Nakajima, and required a fighter capable of reaching a maximum 500 km/h (311 mph), climbing to 5000 m (16 400 It) in five minutes, and having a range of at least 800 km (500 miles). At the same time the Ki 43 was to match Ki 27 in manoeuvrability. Two further 925 hp Nakajima Ha 25 radial engined prototypes were completed and test flown in 1939 and were ready for service trials. To meet the performance requirements further changes were still required to reduce the overall weight and improve maneuverability. The unique combat flaps were designed and handling of the aircraft was well reported on. To reduce the weight the retractable undercarriage was made from ground aluminum and the frame material changed to Alclad 24, a lighter alloy. It possessed neither armour nor self-sealing fuel tanks.

Nakajima Ki-43 Hayabusa Article

They met the army’s speed and climb requirements, but were heavy on the controls and in no way compared with the Ki 27 in manoeuvrability. Ten service test aircraft were accordingly built with various modifications incorporated in each. The development programme was successful and led to the first Ki 43 I production order. The fuselage had been redesigned with a reduced diameter, and changes were made to the tailplane and wings. Specially designed butterfly type combat flaps, tested on the service test machines, gave exceptional manoeuvrability, making the Ki 43 a formidable dogfight opponent a worthy successor to the Ki 27 with an exceptional rate of turn. Two service trials aircraft had been tested with the 1100 hp Ha105 radial, but initial production aircraft retained the Ha 25. Named Hayabusa (Peregrine Falcon) the Ki 43 went into service as the Army Type 1 Fighter. Some were produced as the Ki 43a with twin 7.7 mrn (0.303in) Type 89 machine guns. Others, which were designated Ki 43 Ib, had a 12.7 mm (0.54in) Ho 103 gun in place of one of the 7.7mm weapons.

Very little paint was applied to keep weight at a minimum and later on this was to see a large variety of colour schemes, as most Ki-43’s were sent to combat in bare aluminium, the individual units producing their own schemes of camouflage. Basic factory paint included internal corrosion protection, Hinomaru on the wings – after 1942 it became standard also on the fuselage – and the antiglare forward of the canopy. Most propellers were left bare or in dark brown prime. Individual units often colour coded the spinner and propeller to their unit colours.
In Spring 1940 the two bladed wooden propeller was replaced with a metal two bladed propeller, similar to a Hamilton Standard.

Production commenced in 1941 at Nakajimas Ota plant and the Ki-43-Ia reached fighter units some six months later. The first Sentais re equipped with Ki 43s, from August 1941, were the 59th and 64th. From the first day of the Pacific war against Britain and the United States, they were in action over Malaya and Burma, in support of invading Japanese land forces, and were codenamed Oscar by the Allies. Like its navy counterpart, the Mitsubishi A6M Zero, the Ki 43 acquired a reputation of supremacy in the first months of combat.

Some 40 army Ki 43 pilots claimed each to have destroyed at least ten enemy aircraft, and even discounting a proportion of these figures, this was a formidable score. In one encounter on December 22, 1941, aircraft of the 2nd Chutai, 64th Sentai, destroyed five Australian Brewster Buffaloes for the loss of one of their own number. Allied fighters caught in dogfights with experienced Japanese pilots had little chance. Early on, the Ki 43 Ic went into production, with two 12.7mm Ho 103 machine guns, but production of the Ic was terminated after 716 aircraft had appeared.

Five prototypes of the Ki 43 II (codenamed ‘Oscar’ by the Allies) flew in early 1942, and production began in November 1942 at Nakajima’s Ota factory. The weak wing structure of early aircraft had caused a number of crashes, and the new version had a strengthened wing of slightly reduced span. The new 858kW / 1150 hp Nakajima Ha 115 engine was installed, enclosed in a longer chord cowling incorporating the supercharger air intake, which increased the top speed to 530km/h. The armament of the Ki 43 1c was retained. The Ki 43 I was vul¬nerable once it was in an enemy’s sights, and to provide some protection the Ki 43 II had fuel tanks enclosed in rubber while 13 mm (0.51 in) armour protected the pilot’s head and back. The reinforced wings had racks for two 250 kg (550 1b) bombs or 200 litre (44¬Imp gal) drop tanks. Maximum speed was greatly improved without detriment to the aircraft’s flying qualities. Range with maxi¬mum internal fuel rose from 1200 km (750 miles) to 1620 km (1000 miles) in the Ki 43 II. With drop tanks, range rose to a remarkable 3000 km (1860 miles) at 400 km/h (248 mph) cruise speed. Further modifications in the Ki-¬43 IIb model were only minor. Three Ki 43 II Kai prototypes had ejector type engine exhaust stubs in place of the conventional collector ring of Ki 43 II. Deliveries to opera¬tional Sentais began in mid 1943.

The armament consisted of 2 x 7.7 mm Type 80 machine guns initially, later to be improved to 1 x 7.7mm and 1 x 12.7mm, each with 250 rounds. The Type 2 Ki-43 saw the armament with 2 x 12.7mm and the Type 3 with 2 x 20mm Ho-5 cannons replac¬ing the 12.7mm. Racks for two bombs of 250 kg each were found on the wings, however this fighter’s main disadvantage throughout combat was to be the inadequate armament.

The Ki-43-IIb entered mass production in November 1942, first with Nakajima and six months later with Tachikawa.

The 14 cylinder double row radial engine, with a round shaped oil cooler, was one of the superior engines created by Nakajima, namely Ha-25 Type 99 rated at 980 h.p and the later improved Ha-115 power plant with a two speed super¬charger and driving a three bladed propeller. The later Ha¬il 5 air intake was moved from under the cowling to its upper lip.

Final variant was the Ki-43-III with 917kW engine and a top speed of 576km/h, but relatively few examples reached operational units. Ten Ki 43 III prototypes were followed by production Ki 43 IIIa machines from Tachikawa, who had already joined the pro¬duction programme of Ki 43 IIs, allowing Nakajima to switch entirely to production of the Ki 84 Hayate. The Ki 43 III differed mainly in its 1230 hp Ha 115 II engine. The armament was still two 12.7 mm guns.

The final version was the Tachikawa-developed Ki.43-IIIb, the first and only version to include 20mm cannon in its armament, but only two of these had been completed by VJ day.

A captured Ki 43 II had been thoroughly tested and examined in Australia, and Allied pilots were given much valuable guidance on the aircraft’s weak points. This helped to alter the balance in favour of Allied aircraft. Early on, the 50th Sentai, flying over Burma, produced outstanding Ki 43 pilots, notably Sergeant Satoshi Anabuki who scored 50 kills in 18 months, and pilots Isamu Sasaki and Yukio Shimokawa who claimed 32 and 15 victories respectively. But as the war moved against Japan, Ki 43 losses began to soar as they were confronted by improved Allied fighters and better trained pilots. Tachikawa continued to produce the Ki 43 until the end of the war. Production of all versions from all manufacturers totalled 5919. Many Ki 43s remained in first line service until August 1945. Some Sentais operated them as fighter-¬bombers, while a number were expended in kamikaze attacks.

Second only in numbers to the Navy Zero, a total of 5,919 Ki-43s including 33 prototypes and trials aircraft, code named Oscar, were manufactured between 1938 and 1945. Tachikawa built 2529.

Ki 43 prototype
Engine: 925 hp Nakajima Ha 25

Ki 43 service trials
Engine: 1100 hp Ha¬105 radial

Ki 43 I / Army Type 1
Engine: 925 hp Nakajima Ha 25

Ki 43a
Engine: 925 hp Nakajima Ha 25
Armament: twin 7.7 mrn (0.303¬in) Type 89 machine guns. each with 250 rounds
Range internal fuel: 1200 km (750 miles)

Ki-43-1
Engine: Nakajima Ha-25, 990 hp.
Max speed: 495 km/h at 4,000m
Cruise: 320 km/h at 2,500m
Max range: 745 miles
Armament: 2 x 12.7mm mg

Ki 43 Ib
Engine: Nakajima Ha-25, 990 hp.
Range internal fuel: 1200 km (750 miles)
Armament: 1 x 7.7 mrn (0.303¬in) Type 89 machine gun, 1 x 12.7 mm (0.54in) Ho 103 gun

Ki 43 Ic
Engine: Nakajima Ha-25, 990 hp.
Span: 11.44 m (37 ft 6 in)
Length: 8.83 m (29 ft)
Gross weight: 2048 kg (4515 lb)
Maximum speed: 492 km/h (306 mph)
Range internal fuel: 1200 km (750 miles)
Armament: two 12.7¬mm Ho 103 machine guns

Ki 43 II
Engine: 858kW / 1150 hp Nakajima Ha 115
Top speed: 530km/h
Range internal fuel: 1200 km (750 miles)
Armament two 12.7¬mm Ho 103 machine guns

Ki 43 II
Engine: 858kW / 1150 hp Nakajima Ha 115
External load: two 250 kg (550 1b) bombs or 200 litre (44¬Imp gal) drop tanks
Range internal fuel: 1620 km (1000 miles)
Range w/drop tanks: 3000 km (1860 miles) at 400 km/h (248 mph)

Ki 43 IIb
Engine: 1 x Nakajima Ha-115, 858kW / 1130 hp
Span: 10.84 m (35 ft 7 in)
Length: 8.92 m (29 ft 3 in)
Height: 3.27 m / 10 ft 9 in
Wing area: 21.4 sq.m / 230.35 sq ft
Max take-off weight: 2590 kg / 5710 lb
Empty weight: 1910 kg / 4211 lb
Ceiling: 11200 m / 36750 ft
Range w/max.fuel: 3200 km / 1988 miles
Maximum speed: 530 km/h (329 mph) at 19,680 ft
Crew: 1
Armament: 2 x 12.7mm machine-guns, 2 x 250-kg bombs

Ki 43 II Kai

Ki-43-IIb

Ki-43-III
Engine 917kW / 1230 hp Sakae Ha 115 II
External: two 250 kg bombs
Top speed: 576km/h
Armament: 2 x 20mm Ho-5 cannons

Ki 43 IIIa
Engine 917kW / 1230 hp Sakae Ha 115 II
Armament: two 12.7 mm guns.
Max speed: 358 mph.

At a time when the triumphs of the B5N were still almost three years in the future, the Japanese navy issued a specification for a replacement, recognizing that only limited overall design improvement of the B5N could be achieved in the B5N2. Accordingly design went ahead in 1939 of the Nakajima B6N and, despite the Navy’s preference for the Mitsubishsi Kasei radial, a Nakajima Mamoru was selected for the prototype which flew on 14 March 1941, demonstrating several problems, notably the poor engine reliability. With the delay of 2 years, by 1943 the engine had improved to the point where serial production was allowed to start, but after only 133 B6N1s had been delivered the Navy ordered the switch to the 1,850 hp (1380 kW) Mitsubishi MK4T Kasei 25. The rest of the 1,268 B6N2s were Kasei powered.

Superficially the B6N Tenzan (Heavenly Mountain) resembled the earlier aircraft, but the much increased power and torque of the big engine and four-blade propeller was found to impose considerable directional stability problems, demanding that the vertical tail surfaces be offset to one side. Flight trials dragged on, and were further delayed by troubles during carrier acceptance tests. Then Nakajima was ordered to stop production of the Mamoru engine, so modifications had to be introduced to suit installation of the Kasei.

In due course B6N1 aircraft (of which only 133 were built) were embarked in the carriers Shokaku, Taiho, Hiyo, Junyo and Zuikaku, and took part in the Battle of the Philippine Sea of June 1943, many being lost when the three Shokaku, Taiho, and Hiyo were sunk.

In that month production started of the slightly improved B6N2 (of which 1,133 were produced before the end of the war), but the heavy losses among Japanese carriers resulted in the ‘Jill’ being largely deployed ashore, particularly after the Battle of Leyte Gulf. Thereafter many BsNs were consigned to the kamikaze role.

B6N2
Engine: 1 x Mitsubishi MK4T “Kasei-25”, 1850 hp
Wingspan: 14.9 m / 48 ft 11 in
Wing area: 37.2 sq.m / 400.42 sq ft
Length: 10.87 m / 35 ft 8 in
Height: 3.8 m / 12 ft 6 in
Empty weight: 3010 kg / 6636 lb
Max take-off weight: 5650 kg / 12456 lb
Max. speed: 480 km/h / 298 mph at 16,076 ft
Ceiling: 9040 m / 29650 ft
Service ceiling: 26,660 ft
Range w/max.fuel: 3045 km / 1892 miles
Armament: 1 x 13 mm, 2 x 7.9mm machine-guns
Bomb load: 1 x 1764 lb torpedo or 6 x 220 lb bombs
Crew: 3