Claire Chennault's American Volunteer Group—later immortalized as the "Flying Tigers"—had trained in Burma from mid-1941 but first saw combat on 20 December 1941—13 days after Pearl Harbor made the U.S. officially part of the war. Chennault, a retired Army Air Corps major with a hearing disability, had spent years studying Japanese fighter tactics in China. He drilled his pilots in the P-40's strengths: dive, fire, zoom away. Never turn with a Zero. Over Rangoon and Kunming between December 1941 and July 1942, the AVG claimed 297 Japanese aircraft destroyed at a cost of 14 pilots. Winston Churchill compared their victories to the Battle of Britain. Chennault's pay scale was unorthodox—$600 a month and a $500 bonus per kill—but his tactics were sound. The Flying Tigers proved that American pilots, properly trained, could beat the Imperial Japanese Air Force. The Army Air Forces spent the rest of the war trying to forget that a civilian contractor had figured it out first.