The Mitsubishi A6M Zero-Sen, the most famous of all Japanese combat aircraft, possessed the unique distinction of being the first carrier-based fighter ever to outperform corresponding land-based machines; it was also a singularly unpleasant shock to US and British military staff which had apparently never studied the behaviour of this fighter in China or even discovered its existence!
It was designed by Mitsubishi to meet the severe demands of the 1937 Navy carrier-based fighter specification, seeking a successor to the A5M. Demands included a speed of 500 km/h (311 mph) and armament of two cannon and two machine guns. Under team leader Jiro Horikoshi the new fighter took shape as a clean, efficient but lightly built aircraft with outstanding manoeuvrability. With a more powerful engine it was accepted for production as the A6M2, though as it was put into production in 1940, the Japanese year 5700, it became popularly the Zero-Sen (Type 00 fighter), and to millions of its enemies was simply the "Zero" (although the official Allied code name was "Zeke"). Before official trials were completed two squadrons with 15 aircraft were sent to China in July 1940 for trials under operational conditions. They eliminated all opposition, as forcefully reported to Washington by General Claire Chennault, commander of the Flying Tigers volunteer force (his warning was obviously filed before being read). More than 400 had been delivered by the time the A6M2 and clipped-wing M3 appeared at Pearl Harbor. During the subsequent year it seemed that thousands of these fighters were in use, their unrivalled manoeuvrability being matched by unparalleled range with a small engine, 156 gal internal fuel and drop tanks. So completely did the A6M sweep away Allied air power that the Japanese nation came to believe it was invincible.
After the Battle of Midway the Allies slowly gained the ascendancy, and the A6M found itself outclassed by the F4U and F6F. Mitsubishi urgently tried to devise improved versions and the A6M5 was built in quantities far greater than any other Japanese combat aircraft. Improvements were mainly small and the combat-boosted Sakae 31 engine did not appear until the end of 1944. Only a few of the much more powerful A6M8c type were produced, the main reason for this change of engine being the destruction of the Nakajima factory. The final model was the A6M7 Kamikaze version, though hundreds of Zeros of many sub-types were converted for suicide attacks. Total production amounted to 10,937, of which 6,217 were built by Nakajima which also designed and built 327 of the attractive A6M2-N single-float seaplane fighter version (code-name "Rufe") which operated throughout the Pacific war. The A6M2-K was one of several dual-seat trainer versions.