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The Mitsubishi A7M Reppu (Hurricane) 'Sam' was designed to be the replacement for the A6M Zero, but despite a great deal of effort over several years only one production aircraft was completed before the end of the Second World War.
Although the A6M Zero had more than lived up to expectations, even as it was being introduced the Japanese Navy began to think about a replacement. A 16-Shi specification for a new fighter was issued, but Mitsubishi struggled to find the staff to work on the project, and the specification was withdrawn.
Work resumed in 1942, this time to a 17-Shi specification issued on 6 July 1942. This was designed to make sure that the aircraft wouldn't be obsolete by the time it was introduced, probably no earlier than 1945. The new aircraft was thus required to have a top speed of 397mph at 19,685ft, to be able to climb to that height in 6 minutes, to have an endurance of 2hr 30mins at 288mph, a diving speed of 518mph, to be armed with two 20mm cannon and two 13.2mm machine guns. It also had to be as manoeuvrable as the A6M3 Model 32.
Jiro Horikoshi, the main Mitsubishi designer, believed that in order to achieve this impressive performance the aircraft would have to use the new Mitsubishi MK9A or MK9B 18 cylinder radial engine, itself still under development in 1942. The Navy disagreed, and ordered Mitsubishi to use the NK9K Homare engine, perhaps aware of the dangers of relying on an untested engine.
The first prototype, designated as the A7M1, was not ready for its maiden flight until 6 May 1944. It was a fairly typical radial engined fighter of the period, with a cut down fuselage and domed cockpit canopy, giving a good view in every direction. The wings had a flat central section, with dihedral on the outer panels. The wings were very large compared to the A6M5, with a span of 45ft 11 3/16in and a total area of 332.173sq ft. Tests with the prototype proved that the basic design was sound, with good stability and manoeuvrability, but the Homare engine was even more disappointing than Jiro Horikoshi had feared, and the aircraft fell 50mph short of its top speed while its climb rate was nearly twice as slow as required. On 30 July 1944 Mitsubishi were ordered to stop work on the next third to sixth prototypes until a more suitable engine could be found.
Just as Jiro Horikoshi had believed two years earlier that engine turned out to be the Mitsubishi MK9A. The sixth A7M1 prototype was re-engined to become the first of seven A7M2 prototypes and development aircraft. The re-engined prototype made its maiden flight on 13 October, and this time the aircraft was a success. It was ordered into production as the Navy Carrier Fighter Reppu Model 22, with production to be split between Nagoya and Osaka while the engines were built at the Daiko engine factory.
From now on nature and the Americans conspired against the A7M. A massive earthquake hit the Nagoya area, causing many delays. The B-29s bombed the Daiko engine factory, massively reducing the supply of MK9A engines. The first, third and fifth prototypes were also destroyed by American bombing and the second prototype crashed. Only three prototypes were still intact at the end of the war, and only one production aircraft had been completed.
Variants
A7M1
The first two prototypes, with the underpowered Nakajima Homare engine.
A7M2
The planned production version, armed with either two 13.2mm machine guns and two 20mm cannon or four 20mm cannon.
A7M3
A version to be armed with six wing-mounted 20mm cannon and a mechanically drive three-speed supercharger, designed in case the more radical A7M3-J failed. The first prototype was expected to be completed in December 1945.
A7M3-J
The A7M3-J was to have been a land based interceptor version of the A7M. Work on it began early in 1944, with an emphasis on increasing the rate of climb and performance at high altitude. The A7M3-J was to be armed with four wing mounted 30mm cannon and two obliquely mounted 30mm cannon carried in the rear fuselage. Both the fuselage and wings needed major modifications to carry these larger guns. The aircraft was to be powered by a turbo-supercharged engine and was expected to reach 403mph at 32,810ft. A mock-up was completed early in 1945, but the first prototype wasn't expected until October 1945.
Specification (A7M2)
Engine: Mitsubishi MK9A eighteen cylinder air-cooled radial engine
Power: 2,200hp at take off, 2,070hp at 3,280ft, 1,800hp at 19,685ft
Crew: 1
Wing span: 45ft 11 3/16in
Length: 36ft 1 1/16in
Height: 14ft 0 1/2in
Empty Weight: 7,112lb
Loaded Weight: 10,406lb
Max Speed: 390mph at 21,655ft
Cruising Speed: 259mph at 13,125ft
Service Ceiling: 35,760ft
Endurance: 2.5 hours at cruising speed plus 30 minutes combat
Armament: Either two 20mm cannon and two 13.2mm machine guns or four 20mm cannon, all wing mounted
Bomb-load: Two 551lb bombs or two 77 gallon drop tanks