Which nation's air force fought the Battle of Britain against the Luftwaffe?

The RAF, and the pilots were much less exclusively British than the name suggests - Polish, Czechoslovak, Canadian, Australian, New Zealand, South African, Belgian, French, Irish and American aircrew flew in it. The Polish 303 Squadron recorded the highest number of kills of any squadron in the battle.

It was won by a system rather than by aircraft. Britain had built the Dowding System: a chain of radar stations along the coast, feeding into filter rooms with the Observer Corps, feeding into operations rooms that could direct specific squadrons to specific raids. Without it fighters would have had to patrol constantly and would have been exhausted and out of position; with it they were sent where the bombers actually were. It was the first integrated air defence network anywhere.

The margin was genuinely thin, and the closest run was the attack on the airfields and radar stations in late August - which the Luftwaffe abandoned in early September in favour of bombing London, in reprisal for a raid on Berlin. That decision took the pressure off Fighter Command at close to its breaking point. Churchill's line about so much owed by so many to so few was delivered while the battle was still being fought.