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Mitsubishi A6M Reisen
'Zero'
Aircraft Series

Introduction

Genesis and Development

War Prize

The Lean Years

Aircraft Identity

Colour Schemes

Power Plant

Armament

Avionics

Zero and its Opponents

Preserved Zeros

Links

References & Acknowledgments

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All text material on this site is
© Peter Lewis
1985, 1999
unless otherwise acknowledged

    

 

Development of the A6M Series

The Japanese Navy were among the pioneers in the use of carrier-borne fighter aircraft, launching the world's first true aircraft carrier in November 1921, preceding the British HMS Argus by several months. To equip this vessel, Mitsubishi developed the Type 10 fighter, the first designed specifically for carrier operation - naval aircraft of other nations at that time were adaptations of existing land-based fighters. The Type 10 served until 1929, when replaced by the Type 3 fighter, which was a Nakajima-built adaptation of the British Gloster Gambet. This aircraft was re-designated the A1N1 while in service, 'A' signifies carrier-based fighter, and 'N' denotes Nakajima manufacture.
The A1N1 was followed by the 1931 Nakajima Type 90 (A2N) biplane and the 1935 Type 95 (A4N) which was faster but less agile. Mitsubishi then reclaimed the market from Nakajima with the Type 96 Mitsubishi A5N(A5N) all-metal monoplane fighter. Replacing the earlier A2N and A4N biplanes, they were superior to all opposition aircraft encountered in the escalating war over the Chinese mainland. Equally as important, the Type 96 gave Japanese designers, engineers and craftsmen experience with techniques such as minimising drag, flush riveting, weight saving, and the installation of radial engines into high-speed airframes.
Even as the Type 96 was put into service in 1937, it was realised that the Navy required a fighter of much greater range for deep penetration escort duties in China, and that the Type 96 would soon be obsolete compared to American and European equipment, which was already being fitted with retractable landing gear and much heavier firepower.
Coupled with this realisation of the limitations of the over-land performance of the Type 96, was a shift in the beliefs held by the Japanese Naval Command on the theory and practice of naval aviation. Tradition held that naval aircraft were an adjunct to the big gun; useful for reconnaissance, defence, spotting and hindering the enemy until the battleships could be bought to bear on him. This viewpoint, which had been destroyed in respect to land-based aviation by World War 1, was prevalent among other Naval powers until well into World War 2. By adopting the philosophy of the naval air force as an independent arm - fighting and securing superiority well beyond the reach of naval artillery - the Japanese were several years ahead of other nations in producing a series of specialised aircraft well suited to specific tasks. This was at variance with the multirole aircraft concept adopted by other naval powers, a concept that led to such machines as the Fairey Swordfish.
As a result of these experiences and discussions, the Imperial Navy in 1937 issued specifications for the 12-Shi (12th year since Emperor Hirohito's reign started in 1926) carrier-borne fighter. These specifications demanded speed, rate of climb and armament equal to the highest levels in the world, coupled with unheard of range and exceptional maneuverability. Mitsubishi formed a design team under Jiro Horikoshi to study the proposal. Nakajima decided that the Navy's demands were impossible, and told them that they were withdrawing from the competition.
Horikoshi, having retained and strengthened the Type 96 design team, had the project formulated by January 1938. Yoshitoshi Sone and Teruo Tojo performed the calculations, Sone and Yoshio Yoshikawa did the structural work, Denichiro Inoue and Shotaro Tanaka designed the powerplant installation, Yoshimi Hatakenaka handled armament and ancillary equipment, and Sadahiko Kato and Takeyoshi Mori were responsible for landing gear and related equipment. The Mitsubishi MK2 Zuisei 13 of 875hp was selected, and advanced techniques utilising extra-super duralumin to ensure lightness, simplicity and utility were employed. As the specification called only for attack - and Japanese military philosophy reinforced this viewpoint - safety devices such as pilot armour and self-sealing fuel tanks were ignored. Armament was to be a pair of licence-built Oerlikon 20mm cannon (Type 99) in the wings and two 7.7mm machine guns (Type 97 ) in the fuselage.
Construction of the first prototype began later that year and was completed in March 1939. With no provision for armour, lightness of airframe, and lack of heavy fittings, the prototype Type 0 weighed 43801b compared to the prototype Spitfire's 5332lb. Light weight and modest power gave long range and good performance, but meant that substantially heavier and more powerful engines could not be fitted without extensive redesign. As an offensive, rather than a defensive, weapon the Zero' s very success contained the seeds of its own downfall.
The prototype was declared ready for tests at Mitsubishi's Nagoya factory on 16th March 1939. Engine tests were run on the 18th, and the next day it was towed (by ox-cart!) to the airfield at Kagamigahara. Test pilot Katsuzo Shima lifted it off at 5.30pm on 1st April for the initial flight. After correction of braking and vibration problems, official tests of the A6M1 took place and a second, identical prototype was built. Apart from its lack of outright speed - 304mph instead of the required 315mph - all requirements were met, and the A6M1 was officially accepted by the Navy on the 14th September 1939. Its military designation became A6M1 Type 0 Carrier-borne Fighter.
The '0' was derived from the last digit of the Japanese calendar year in which the aircraft would be placed in full service, 2600 (equivalent to 1940); in Japanese this became Rei Shiki Sento Ki, Type Zero Fighter, often shortened to Rei-Sen or Reisen. During the 1940s, the Allies applied code-names to all known Japanese aircraft, and the A6M2 became 'Zeke', the later clip-wing A6@13-72 'Hamp', the A6M3-22 'Zeke Mark 2' and the A6M2-N floatplane version 'Rufe'. By this time the term 'Zero' was already popular (although British personnel in the Singapore/Malaya theatre initially knew them as 'Navy Noughts'), and even today people identify virtually any low-wing radial-engined Japanese fighter as a 'Zero'.
In order to solve the lack of speed in the A6M1, the A6M2 with the 940hp Nakajima Sakae 12 motor was designed, andA6M2 in China 15 pre-production machines were dispatched to Hankow in China for operational trials on 21 July 1940. Sixteen months before Pearl Harbour, the Zero flew its first combat mission. Such was the superiority over the Chinese fighters that the Chinese refused to fight. Only two Zeros were lost to enemy activity in this period, shot down by anti- aircraft fire.
Mitsubishi built another 47 A6M2 Model 11 aircraft by November 1940 before introducing the Model 21, which incorporated folding wingtips. Under the 'Model' designation system, a change in the first digit denoted an airframe change, alteration of the second digit denoted an engine change. Thus the Model 'two one' showed that it differed structurally from the Model 'one one' but retained the same motor. The A6M2 Model 21 was the standard JNAF fighter at the time of the attack on Pearl Harbour, 328 of this model being amongst the 521 naval fighters on board the Japanese aircraft carriers at that time.
Further models of the A6M were introduced to overcome problems and design limitations, and to try to keep the superiority that the type enjoyed over contemporary Allied aircraft:
A6M3 Model 32: Engine change to 1130hp Sakae 21, and removal of the folding wingtip section, giving a clipped wing. To retain the centre of gravity position with the heavier engine, the latter was moved back towards the bulkhead. This reduced the fuel tank volume thus reducing the combat radiusModel 22 folding wingtip detail.
A6M3 Model 22: Adding the original folding-tip wing to the Model 32 engine/body combination, and incorporating a 12 gallon fuel tank in each wing in an attempt to reclaim lost range. By the time the Model 22 reached production, the Model 52 was approaching operational status; thus the Model 22, appearing in combat after the Model 32, had a short operational life. 560 were built late 1942 and early 1943 (this figure is thought to include Nakajima production).
A6M5 Model 52: Similar to the Model 32, but with some weight saving measures in the wing structure, heavier gauge wing skins to allow higher dive speed, individual exhaust stacks for additional thrust. The most numerous and widely used version of the Zero.
By the time that the Model 52 became outdated - 1944 - further modifications of the basic design began to display an air of desperation. New designs such as the A7M Reppu, J2M Raiden and N1K Shiden could not be debugged or produced in sufficient volume, so the Zero had to soldier on. The A6M4 (turbo-supercharged engine) A6M6 {water-methanol injection) A6M7 (fighter-bomber version) A6M8 (1350hp Kinsei engine) were all built in varying quantities, but against the American Wildcat, Hellcat and Corsair carrier-based fighters they and their inexperienced pilots had little chance of success. By the end of the war more Zero fighters had been built by Japan than any other type of aircraft. Mitsubishi had produced 3879, but the majority were constructed by Nakajima who assembled 6215. Added to this were 844 trainers and floatplanes for a total of 10938 aircraft. After the cessation of hostilities a few Zeros flew briefly for evaluation in some Allied air forces, and for a short while longer in Indo-China and Indonesia.