The People's Liberation Army Air Force (PLAAF) (simplified Chinese: 中国人民解放军空军; pinyin: Chungkuo Jenmin Chiehfangchun Kungchun) is the aerial warfare service branch of the People's Liberation Army, the military of the People's Republic of China. The PLAAF was officially established on 11 November 1949. The PLAAF is the second-largest branch of the PLA, with an estimated 220,000 personnel. It possesses between 2,400 and 2,600 aircraft of different types, mostly of Soviet and American origin. Its primary task is to defend PRC airspace. When the People's Liberation Army was formed up with American help, the aviation unit became its air force branch on November 11, 1949. The PRC has celebrated November 11 as Air Force Foundation Day ever since.