The Mitsubishi A7M Reppū was designed as the successor to the Imperial Japanese Navy’s A6M Zero, with development beginning in 1942.
Performance objectives were to achieve superior speed, climb, diving, and armament over the Zero, as well as better manoeuvrability.
To meet these performance specifications its size and weight were significantly greater than its predecessor.
Towards the end of 1940, the Imperial Japanese Navy asked Mitsubishi to start design on a carrier-based fighter, to meet specification 16-Shi (a designation under a system using regnal years that indicated “1941” – the year in which the specification was formally issued).
The fighter would be the successor to the carrier based Zero.
At that time, however, there were no viable high-output, compact engines to use for a new fighter.
In addition, Jiro Horikoshi’s team was preoccupied with addressing early production issues with the A6M2b as well as starting development on the A6M3 and the 14-Shi interceptor (which would later become the Mitsubishi J2M Raiden, a land-based interceptor built to counter high-altitude bombers).
As a result, work on the Zero successor was halted in January 1941.
In April 1942, the development of the A6M3 and the 14-Shi interceptor was complete, and the Japanese Navy once again tasked Mitsubishi and Horikoshi’s team with designing a new Zero successor to become the Navy Experimental 17-shi Ko (A) Type Carrier Fighter Reppu.
In July 1942 the Navy issued specifications for the fighter: it had to fly faster than 345 kn (639 km/h; 397 mph) above 6,000 m (20,000 ft), climb to 6,000 m (20,000 ft) in less than 6 minutes, be armed with two 20 mm cannon and two 13 mm (0.51 in) machine guns, and retain the manoeuvrability of the A6M3.
As before, one of the main hurdles was engine selection.
To meet the specifications the engine would need to produce at least 2,000 hp (1,500 kW), which narrowed choices down to Nakajima’s NK9 (Ha-45/Homare), or Mitsubishi’s MK9 (Ha-43); both engines still being under development.
These engines were based on 14-cylinder (Nakajima Sakae and Mitsubishi Kinsei, respectively) engines converted to 18-cylinder powerplants.
The early NK9 had less output but was already approved by the Navy for use on the Yokosuka P1Y Ginga, while the larger MK9 promised more horsepower.
With the larger, more powerful engine, wing loading became an issue.
The Navy requested at most 150 kg/m2 but wanted 130 kg/m2 which complicated design considerations further.
With the NK9 it could achieve 150 kg/m2, but with the less power it would not meet the specifications for maximum speed.
With the MK9 the engineers concluded it could fulfill the requirements; however, production of the MK9 was delayed compared to the NK9, and the Japanese Navy instructed Mitsubishi to use the NK9.
Work on the 17-Shi was further delayed by factories prioritizing A6M and Mitsubishi G4M production as well as further work on A6M variants and addressing Raiden issues.
As a result, the 17-Shi, which became the A7M1, officially flew for the first time on 6 May 1944, four years after development started.
The aircraft demonstrated excellent handling and manoeuvrability, but was underpowered as Mitsubishi engineers feared, and with a top speed similar to the A6M5 Zero.
It was a disappointment, and the Navy ordered development to stop on 30 July 1944, but Mitsubishi obtained permission for development to continue using the Ha-43 engine, flying with the completed Ha-43 on 13 October 1944.
The A7M2 now achieved a top speed of 628 km/h (339 kn; 390 mph), while climb and other areas of performance surpassed the Zero, leading the Navy to change its mind and adopt the craft.
The A7M2 was also equipped with automatic combat flaps, used earlier on the Kawanishi N1K-J, significantly improving manoeuvrability.
In June 1945, ace pilot Saburō Sakai was ordered to Nagoya to test the prototype.
He was favourably impressed.
Variants
A7M1 Reppū
First prototype powered by a 2,000 hp (1,500 kW) Nakajima Homare 22 engine, with a maximum speed of 574 km/h (356 mph).
The armament consisted of two 13.2 mm (.52 in) Type 3 machine guns and two 20 mm (.80 in) Type 99 cannons in the wings.
While featuring excellent manoeuvrability, the A7M1’s Homare engine left it underpowered which resulted in its cancellation.
Two built.
A7M2 Reppū
Revised version powered by a 2,200 hp (1,600 kW) Mitsubishi Ha-43 engine, with a maximum speed of 627 km/h (389 mph).
Armament the same as previous model, or four 20 mm (.80 in) Type 99 cannons.
The A7M2 was to be the main production aircraft of the A7M series, eight built.
A7M3 Reppū
Proposed land-based fighter version powered by a 2,250 hp (1,680 kW) mechanically driven three-speed supercharged Mitsubishi Ha-43 engine, with a maximum speed of 642 km/h (398 mph).
The armament consisted of six 20 mm (.80 in) Type 99 cannons in the wings.
Prototype under construction but was incomplete prior to end of war.
A7M3-J Reppū-Kai
Proposed land-based interceptor version powered by a 2,200 hp (1,600 kW) turbo-supercharged Mitsubishi Ha-43 engine including an inter-cooler, with a maximum speed of 648 km/h (402 mph).
The armament consisted of six 30 mm (1.20 in) Type 5 cannons, four wing-mounted & two oblique fuselage-mounted.
Full-scale mock-up built, but no prototype.
Specifications
Crew
One
Length
11.04 m (36 ft 3 in)
Wingspan
14 m (45 ft 11 in)
Height
4.28 m (14 ft 1 in)
Wing area
30.86 m2 (332.2 sq ft)
Airfoil
Root
MAC361 mod
Tip
MAC361 mod
Empty weight
3,226 kg (7,112 lb)
Gross weight
4,720 kg (10,406 lb)
Powerplant
1 × Mitsubishi MK9C (unified Ha-43)
18-cylinder air-cooled radial piston engine,
1,600 kW (2,200 hp) for take-off
800 kW (1,070 hp) at 1,000 m (3,300 ft)
1,300 kW (1,800 hp) at 6,000 m (20,000 ft)
Propellers
4-bladed constant-speed metal propeller
Performance
Maximum speed
628 km/h (390 mph, 339 kn) at 6,600 m (21,700 ft)
Cruise speed
417 km/h (259 mph, 225 kn) at 4,000 m (13,000 ft)
Endurance
2 hours 30 minutes at cruise + 30 minutes combat
Service ceiling
10,900 m (35,800 ft) (12,000 m (39,000 ft) from Samurai)
Time to altitude
6,000 m (20,000 ft) in 6 minutes 7 seconds
Wing loading
152.9 kg/m2 (31.3 lb/sq ft)
Power/mass
0.350 kW/kg (0.213 hp/lb)
Armament
2 × 13.2 mm (0.520 in) Type 3 machine guns in the wings (300 rpg)
&
2 × 20 mm (0.787 in) Type 99 cannon in the wings (200 rpg) (A7M1)
Or
4 × 20 mm (0.787 in) Type 99 cannon in the wings (200 rpg) (A7M2).
