In 1940 seven Americans volunteered for the British Royal Air Force in time to fly and fight in the Battle of Britain. Within a year, by the time the Japanese attack on Pearl Harbor brought the United States abruptly into World War II, 243 other Americans flew for the Royal Air Force in three Eagle Squadrons, units that in early 1942 became the nucleus of the United States Army Air Force's 4th Fighter Group. American combat in the European and Mediterranean theaters of.