As in WWI, numerous Americans took advantage of the opportunity to fly and fight without waiting upon their country to enter the war. In Burma, Claire L. Chennault, a retired Air Corps major who had served as special advisor to the Chinese Air Force since 1937, formed the American Volunteer Group (A.V.G) nicknamed the Flying Tigers. The unit consisted of approximately 100 pilots and 200 ground crew personnel (most of whom had been released from the U.S. Army, Navy, and Marines to volunteer for the A.V.G.) and was equipped with obsolescent P-40B airplanes. It began training at Rangoon in Sep. 1941.

Two of the three squadrons moved to Kunming, China to protect the Burma Road, the only ground route into China, and on Dec. 20, 1941, the Flying Tigers received their "baptism under fire" when they inflicted heavy losses on Japanese bombers attempting to attack Kunming. Months of combat followed and the A.V.G., greatly outnumbered in the air and operating under adverse conditions (such as no replacement pilots and practically no spare parts for repairing aircraft), scored a very impressive record against the enemy, 286 Japanese planes shot down at a cost of 12 A.V.G. pilots killed or missing in action. In May 1942, pilots of the 23rd Fighter Group, selected to replace the Flying Tigers, began to arrive in China and the A.V.G. was dissolved on Jul. 4, 1942 when the 23rd Group was officially activated.