Summer 1940. France is gone. Britain, with its empire and dominions behind it, faces Germany without an ally left in Europe. If the Luftwaffe owns the sky, the invasion barges can come. Some three thousand airmen, British, Commonwealth, and Polish and Czech exiles, fight over southern England, guided by a radar chain the Germans do not understand.
Why then
Dunkirk saved the army, and Hitler expects London to make a deal. When it does not, control of the air becomes the condition for invasion. The fight that matters is for airfields and radar stations in daylight.
What they wanted
Göring promises to destroy the RAF in weeks. Churchill needs a public that can see standing alone as a job. Dowding, who runs Fighter Command, husbands his pilots and aircraft and refuses to throw them away.
What changed
In September the Luftwaffe turns on London. The Blitz kills over 40,000 civilians by May 1941, but the RAF is still flying, British factories are out-building German ones, and the invasion is postponed and then dropped.
Still argued
Stephen Bungay argues Fighter Command was never near collapse and won as a system of radar, factories and training more than by luck. The older legend has a few exhausted pilots on the brink.