'Never in the field of human conflict has so much been owed by so many to so few'.

On this day 18th August 1940, 75 years ago the hardest day of the Battle of britain was fought.

'On this day the Luftwaffe tried its utmost to destroy our fighter airfields flying 850 sorties involving 2200 aircrew. The RAF resisted with equal vigour flying 927 sorties involving 600 aircrew.'  

More here RAF museum: The Hardest Day

The few consisted of 2,353 British pilots and various other nations as below (In order of number of pilots)  More here: Non-British personnel in the RAF during the Battle of Britain

Nation	Number
Poland	145[1]
New Zealand	127[1] or 135[2]
Canada	112[1]
Czechoslovakia	84[3] or 88[1]
Belgium	28[1] or 30[3]
Australia	26[3] or 32[1]
South Africa	22[3] or 25[1]
France	13[1] or 14[3]
Ireland	10[1]
United States	9[1] or 11[3]
Southern Rhodesia	3[1] or 4[3]
Northern Rhodesia	1[3]
Barbados	1[1]
Jamaica	1[1]
Newfoundland	1[1]

Part of Churchill's speech on 20 August 1940 -  More Here
'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 by their devotion. Never in the field of human conflict was so much owed by so many to so few. All hearts go out to the fighter pilots, whose brilliant actions we see with our own eyes day after day, but we must never forget that all the time, night after night, month after month, our bomber squadrons travel far into Germany, find their targets in the darkness by the highest navigational skill, aim their attacks, often under the heaviest fire, often with serious loss, with deliberate, careful discrimination, and inflict shattering blows upon the whole of the technical and war-making structure of the Nazi power. On no part of the Royal Air Force does the weight of the war fall more heavily than on the daylight bombers who will play an invaluable part in the case of invasion and whose unflinching zeal it has been necessary in the meanwhile on numerous occasions to restrain…'

 — Winston Churchill

Flypast to mark 'hardest day' of Battle of Britain BBC News

 

https://en.wikipedia.org/wiki/The_Hardest_Day

Prior to 'the few' speech Churchill delivered his battle of Britain speech on 18th June https://en.wikipedia.org/wiki/Battle_of_Britain

... What General Weygand has called The Battle of France is over. The battle of Britain is about to begin. Upon this battle depends the survival of Christian civilisation. Upon it depends our own British life and the long continuity of our institutions and our Empire. The whole fury and might of the enemy must very soon be turned on us. Hitler knows that he will have to break us in this island or lose the war. If we can stand up to him, all Europe may be free and the life of the world may move forward into broad, sunlit uplands. But if we fail, then the whole world, including the United States, including all that we have known and cared for, will sink into the abyss of a new Dark Age made more sinister, and perhaps more protracted, by the lights of a perverted science. Let us therefore brace ourselves to our duties, and so bear ourselves that, if the British Empire and its Commonwealth last for a thousand years, men will still say, "This was their finest hour".

— Winston Churchill