The British Royal Air Force ''Eagle Squadrons'' were a series of World War II Fighter Plane Squadrons composed of American Volunteers. They (as did other Countries) were an augmented part of England's stand alone fight against Hitler's vaunted Luftwaffe attacks against England in what was known as The ''Battle of Britain'' (1940).
With Germany occupying many European Countries, most sent their exiled Air Forces to England m- who had declared War on Germany in 1939. England was painfully short of Fighters for it's Air Service. While The United States supplied a large and continual stream of Fighter Planes (The Lend-Lease Act) to England, Her ability to supply trained fighters was taxed. America was considered neutral with regards to the European phase of The War.
Many American Army Air Force pilots were advised (unofficially) that Great Britain was accepting volunteers to fly their planes. Over 200 American Pilots volunteered. Many, who did not qualify for American Military Pilot training, joined The Canadian Royal Air Force. From their they simply transferred over to The RAF.
Named ''Eagle Squadron'' in reference to the American National symbol of The Eagle, (3) Squadrons of Fighters were formed (71st, 121st and 133rd). With half of their number killed in direct action against Germany, the combined Squadrons claimed over 300 kills in their Service. The Squadrons flew a variety of British Fighters, with the iconic ''Spitfire'' being their primary plane. The Squadron was identified (on their Aircraft) with a modified USAAF 5-Star Roundel placed on the craft's fuselage.
With American involvement in WWII (1941) – USAAF Squadrons were sent directly to England in 1942. The Squadrons were absorbed into The American Forces. They still exist today as modern USAF Fighter Squadrons, identified as the 334th, 335th and 336th deployed to different American Fighter Commands.