“Early in WWII, U.S. aviation experts believed that the Zero fighter was a copy or modification of an American or European design, and that the Japanese were incapable of building an airplane with performance superior to U.S. planes. The truth is, the Zero was much of a Japanese design as any airplane of the day could be.
“… The Zero was accepted by the Japanese Navy in July 1940, and designated A6M2. The letter ‘A’ stood for a carrier-based fighter, the numeral ‘6’ indicated that this was the Navy’s sixth carrier-based fighter, while the ‘M’ meant Mitsubishi. The numeral ‘2’ indicated this was the second version of Mitsubishi’s Prototype 12 fighter … The Japanese military traditionally used the last two digits of the current Japanese year (in this case 2600; 1940 by the Western calendar) in naming new aircraft, thus the new design was designated as the ‘Type 00,’ or ‘Zero’ for short.”
– Koga’s Zero: The Fighter that Changed World War II, by Jim Rearden, 1995
From the wiki: “The Mitsubishi A6M “Zero” is a long-range fighter aircraft, manufactured by Mitsubishi Heavy Industries, and operated by the Imperial Japanese Navy from 1940 to 1945. The A6M was designated as the Mitsubishi Navy ‘Type 00’ Carrier Fighter (rei-shiki-kanjō-sentōki), or the Mitsubishi A6M Rei-sen. The A6M was usually referred to by its pilots as the ‘Reisen’ (zero fighter), ’00’ being the last two digits of the Imperial year 2600 (1940) when it entered service with the Imperial Navy. The official Allied reporting name was ‘Zeke’.
“When it was introduced early in World War II, the Zero was considered the most capable carrier-based fighter in the world, combining excellent maneuverability and very long range. In early combat operations, the Zero gained a legendary reputation as a dogfighter but, by mid-1942, a combination of new tactics and the introduction of better equipment enabled Allied pilots to engage the Zero on generally equal terms. By 1943, inherent design weaknesses and the failure to develop more powerful aircraft engines meant that the Zero became less effective against newer enemy fighters, which possessed greater firepower, armor, and speed, and approached the Zero’s maneuverability.
“Although the Mitsubishi A6M was outdated by 1944, design delays and production difficulties of newer Japanese aircraft types meant that it continued to serve in a front line role until the end of the war. During the final year of the War in the Pacific, the Zero was also adapted for use in kamikaze operations. During the course of the war, Japan produced more Zeros than any other model of combat aircraft – more than 11,000 models of 15 variants between 1939-1945.”