[Buckeye30]

Americans commissioned into the RAF or RAFVR received the same rates of pay and allowances ( quarters, rations and uniforms) as the British; for some reason the RCAF rates were higher than the RAF and Dominion AFs.

On the other subject the Citizenship Act of 1907 stated that "..any American citizen shall be deemed to have expatriated himself ...when he has taken an oath of allegiance to any foreign state"; ie. to the King when joining the British services. Immediately after the fall of France in 1940 the attitudes changed , the British stating " oaths of allegiance to the Crown were no longer required of American citizens who entered the army or air force". So they could keep their US citizenship ( I suspect few would want to swear anyway).
Regards
Nick