The A6M entered service in 1940 and became known as the Zero because of the Japanese designation of Type 0 Carrier Fighter. The Zero technology was years ahead of any other fighter and had no problem clearing the skies of opposing aircraft. There were numerous variants of the Zero including the folding wing A6M2 Model 21 designed for carrier operations. The A6M2 was the most produced Japanese aircraft of WWII. As the war went on the Model 21 would be the Zero variant that most Allied pilots would encounter.