The first A6M5 �Zero� was build by the Mitsubishi Jukogyo in 1943. It absolutely was developed to combat heavier built & armed Allied fighters that were knocking the sooner �Zero� out from the sky during 1943. The Nakajima NK1F Sakae 21 motor offered the airplane somewhat better performance, therefore the armament had been changed to 2- 20mm and 2- 13.2mm weapons. These changes didn't replace the possible lack of armor, or the lack of self-sealing fuel tanks. But,despite these shortcomings, over 10,450 had been built, used through the whole war because other models of Japanese aircraft proceeded to own �teething� problems.