Breakdown of aircrews for the Battle of Britain
The RAF Benevolent Fund put out this rather interesting infographic commemorating the Battle of Britain’s 75th Anniversary. It seems the campaign was rather symbolic of the World War itself. Less than 80 percent of the aircrews were from the UK.
Of deference to the graphic however, some 244 Americans served with the three Eagle Squadrons in RAF service between Sept. 1940 and 29 Sept. 1942 when they were absorbed into the USAAF’s Eight Air Force, although only a fraction flew in the Battle of Britian. (Interesting 31 page USAF pdf here on the subject)