Ayao Shirane enrolled in the Imperial Japanese Naval Academy in April 1933, and graduated as part of the 64th class in March 1937. He completed the navy pilot training program and became a fighter pilot in March 1939. He was assigned to the 12th Air Group in Central China in September of that year, and on 19 August 1940 participated in the Bombing of Chongqing. This mission marked the combat debut of the new Mitsubishi A6M Zero fighter, although no aerial opposition was encountered. On 13 September, Shirane led six of Lieutenant Saburō Shindo's 13 Zeros on a bomber escort mission to Hankow. This mission marked the Zero's true baptism of fire, with the Japanese pilots claiming 27 out of 30 Chinese fighters (including one for Shirane) without suffering any losses in return. He was promoted to full Lieutenant in May 1941.