At what stage of the War? In 1914-1916 the RFC would have been overwhelmingly UK-dominated. However, I believe that the statement is true for the RAF in 1918, but it's worth remembering that the number of Australians in RAF squadrons was reduced by the formation of the AFC, which drew off many Australian airmen. Also, the RFC/RAF recruited directly in Canada, where there was a large training organisation, which made it easier for Canadians and Americans to join there. Gareth
I don't know what stage of the war ... but somebody made the statement and I questioned it .... !! thanks for qualifying it ... now it makes sense !!
I believe the (much smaller) RNAS had up to two-thirds Canadian pilots at some stage - possibly mid-1916 to mid 17.