"The gratitude of every home in our Island, in our Empire, and indeed throughout the world, except in the abodes of the guilty, goes out to the British airmen who, undaunted by odds, unwearied in their constant challenge and mortal danger, are turning the tide of the World War by their prowess and their devotion. Never in the field of human conflict was so much owed by so many to so few."
—Winston Churchill, Speech in House of Commons, August 20, 1940

What does Churchill mean when he says, “Never in the field of human conflict was so much owed by so many to so few”?

The British financial debt because of WWII

Even though they were outnumbered, the actions of the British RAF was instrumental in repelling the German invasion of Great Britain

The League of Nations successfully intervening to stop Germany from attacking Great Britain

The effectiveness of the Luftwaffe in defending British territory