The first Zeros (pre-series of 15 A6M2) went into operation with the 12th Rengo Kōkūtai in July 1940. On 13 September 1940, the Zeros scored their first air-to-air victories when 13 A6M2s led by Lieutenant Saburo Shindo, escorting 27 G3M "Nell's medium-heavy bombers on a raid of Chunking, attacked 34 Soviet-built Polikarpov I-15s and I-16s of the Chinese Nationalist Air Force, claimed "all 27" of the Chinese fighters shot down without loss to themselves, however Major Louie Yim-qun had in fact nursed his I-15 riddled with 48 bullet holes back to base, and Lieutenant Gao Youxin claimed to have shot down one of Lt. Shindo's Zeroes, but at most 4 Zeroes sustained some damage in the 1/2 hour-long dogfight over Chunking. By the time they were redeployed a year later, the Zeros had shot down 99 Chinese aircraft (up to 266 according to other sources).