The British knew the attack was coming, they just weren't sure when. For months Hitler had made his intentions clear: He was going to invade the United Kingdom, and that invasion would start with an air assault.
And on July 10, 1940 that assault began. Phase One -- known as Kanalkampf, German for "channel war" -- focused on taking out shipping in the English Channel. The Royal Air Force was there to meet the Luftwaffe, and after the first day the box score was 13 to 7 in favor of the British -- a surprising result for the outnumbered RAF. That day set the tone for the eventual outcome.
The Germans had more qualified fighter pilots than the British, and their front line fighter, the Bf-109 Messerschmidt, was superior to the RAF's Hurricane (which outnumbered the Spitfire in the inventory at the time) in speed and climb performance. However, the Hurricane had a superior turn rate and better firepower, and the British pilots used those elements to their advantage.
The air war wore on for several months, working it's way over land as German bombers attacked both military and civilian targets. When it was finally over the RAF had lost 544 aircrew to the Luftwaffe's 2,500. The damage to population centers like London took decades to repair, and the British repaid the favor by bombing civilian centers when the war moved east over Germany.
Overall, by preventing Germany from gaining air superiority, the British forced Hitler cancel Operation Sea Lion, the planned invasion of Britain.
After a ceremonial "flypast" today over London, Squadron Leader Duncan Mason who participated in the flight told the BBC: "When you think of the Battle of Britain it was one of those pivotal moments of history, it ranks up there with Trafalgar, Waterloo.
"It's actually not just about the RAF but the resilience of the nation showed in the face of enormous adversity."
Prime Minister Winston Churchill famously summed up the Battle of Britain with this quote: "Never in the field of human conflict was so much owed by so many to so few." In the same speech to the House of Commons he also said, ""... if the British Empire and its Commonwealth lasts for a thousand years, men will still say, 'This was their finest hour.'"