The Battle of Britain Explained in 60 Seconds | BFBS

With mainland Europe conquered, Hitler turned his attention to invading Britain. 
To do so he knew that his Luftwaffe needed air superiority. The Royal Air Force would need to be destroyed.

In the Houses of Parliament, British Prime Minister Winston Churchill declared:  
 “The Battle of France is over. I expect that the Battle of Britain is about to begin.… 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.' "

The Nazis might have underestimated the British resolve, the capabilities of the Spitfire and Hurricane fighters and the advantage the RAF would have fighting over home ground.  “Never was so much owed by so many to so few”.