Total production of the Type 52 series consisted of 10,449 aircraft of which Nakajima produced 6,570. It first entered combat in August 1943 at a time when the Japanese forces were withdrawing from previously held islands in the South Pacific. The type 52c was the last of the A6M5 series, and the most effective against Allied aircraft due to its armament configuration three of 13mm machine guns and two 20mm cannons. A total of 93 Type 52 and 52b zeros were field modified to "c" weapons configuration. The 7.7mm machine guns, housed in the cowling of the Zero since its first introduction, proved to be less effective during the latter stages of the conflict, due to the heavier armor protection of allied aircraft, and their self sealing fuel tanks. The 13mm weapon was greatly more effective; however, due to its increased weight, only one of them could be housed in the cowling and one in each wing. The 7.7 machine guns were removed from the cowling and one 13mm gun was mounted on the right hand side. This installation also made necessary the enlarging of the right hand projectile exit and cowling tube input, of the cowling, giving it an unbalanced look when viewed from the top.