Germany had been banned from having an air force after the First World War, but the Luftwaffe was re-established by the Nazi government and by 1940 it was the largest and most formidable air force in the world.
It had suffered heavy losses in the Battle of France, but by August the three air fleets () that would carry out the assault on Britain were at full readiness.
These three Gladiator fighters, from No 87 Squadron, are practicing for the Empire Air Day at RAF Debden, 1938.
To show the crowds just how precise their flying was the aircraft are tied together by ribbon strips.
The key players in this battle were the fighter pilots.
The Germans needed to get sufficient bombers to the targets so that they could inflict crippling damage.
A sustained air assault on Britain would achieve the decisive victory needed to make ‘Sealion’ a possibility – or so the Germans thought.
The RAF had become an independent branch of the British armed forces in 1918.
A side effect of this would be that the RAF had to respond to such attacks and in the resulting 'dog fights' the experienced and seasoned German fighter pilots could decimate the ranks of RAF Fighter Command.
For the British the aim was to deny the Luftwaffe the freedom of action by attacking the incoming raids, get through the protective screen of fighters, and destroy the bombers.