AVG meaning in Military and Defence ?

The American Volunteer Groups were volunteer air units organized by the United States government to aid the Nationalist government of China against Japan in the Second Sino-Japanese War. The only unit to actually see combat was the 1st AVG, popularly known as the Flying Tigers.

To aid the Nationalist government of China and to put pressure on Japan, President Franklin Roosevelt in April 1941 authorized the creation of a clandestine "Special Air Unit" consisting of three combat groups equipped with American aircraft and staffed by aviators and technicians to be recruited from the U.S. Army, Navy and Marine Corps for service in China. The program was fleshed out in the winter of 1940–1941 by Claire Lee Chennault, then an air advisor to the Chinese Nationalist leader Chiang Kai-shek, and Lauchlin Currie, a young economist in the Roosevelt White House. They envisioned a small air corps of 500 combat aircraft, although in the end, the number was reduced to 200 fighters and 66 light bombers.