In 1937, before the outbreak of the Sino-Japanese war, The Chinese Government recruited retired U.S. Army Air Corps officer Chennault as aviation advisor, commissioned as Air Force Colonel, charged with supervising the development of Chinese Air Force and training of pilots. In 1940, Chennault was ordered to create American Volunteer Group comprised of American pilots.
Chennault recruited 100 pilots from the US military and was ready to defense China against Japanese. With the help of President Roosevelt, Chennault purchased 100 Hawk-81A2 (P-40B/C diverted from Royal Air Force order), and began training in Burma in August of 1941.
Although control and climb performance of P-40 is not so good, excellent dive speed and great structural strength is superior to the Japanese fighters. Thus, AVG used to exploit so-called "boom-and-zoom" tactics in combat with Japanese Army's Ki-27 s and Ki-43' s, and advised against prolonged dog fighting. The AVG's kill ratio was superior to Japanese in almost all their engagements.
Along with The United States entry into World War II, The AVG was replaced by 23rd Fighter Group of the US Army Air Forces. The AVG was disbanded on 4th July 1942. Some AVG pilots and ground crews accepted commissions in China remained with the unit to carry on combat mission against Japanese.