The Battle of Britain was primarily the fighting between the British Royal Air Force (RAF) and the German Luftwaffe during the air offensive waged by Germany against the United Kingdom in the second half of 1940.
In June 1940, France was defeated, but Britain refused any agreement with Nazi Germany. Therefore, Hitler ordered his generals to conceive a plan for an invasion of Britain, which received the code-name Operation Sea Lion.
However, first and foremost, the Luftwaffe had to win air superiority at the expense of the Royal Air Force, to protect the invasion forces from British planes and the feared Royal Navy.
The Luftwaffe's strengths before the battle were the numerical superiority and experience of the German pilots. The main German fighter was Messerschmidt Bf 109 - an aircraft with an excellent rate of climb, able to enter into a steep dive due to its injection engine, but with a limited range over the British territory.
The British air defense system was then most sophisticated in the world. Beyond radars and the Dowding system, an advanced feature was that the RAF planes were emitting automatically radio signals for identifying (IFF), so they can be differentiated on radar from enemy aircraft.
Most RAF fighter squadrons were equipped with the sturdy Hawker Hurricane and fewer with the faster Supermarine Spitfire. Both British fighters had the benefit of a shorter turning circle than Bf 109, but their carbureted engines did not allow entering in a lightning dive like the Messerschmidt.
The first stage of the campaign waged by the Germans began in July 1940, when the Luftwaffe attacked convoys in the English Channel to draw the RAF fighters into the battle. As a result, daytime naval traffic through the English Channel was paralyzed.
On August 13, the Germans commenced an operation intended to be decisive against the RAF, code-named Adlerangriff ("Eagle Attack"), attacking several radar stations in southern England. However, the results were far below expectations, most of the radar stations being soon functional again.
Then the Luftwaffe began to focus on attacking the airfields, which brought hard times for the RAF Fighter Command. The British losses of pilots and aircraft, as well as the destruction of the airfields infrastructure, had become problematic.
However, a bombardment executed by the RAF on Berlin triggered Hitler's anger, who demanded bombing London for retaliation. The Germans changed their strategy, focusing on London and other cities, but this allowed the RAF to recover.
On September 15, which was named the Battle of Britain Day, the large number of British fighters defending the London's sky was probably a shock to the German pilots who did not expect that their opponents to have yet so many pilots and planes.
Following massive losses suffered in daytime raids, the Germans would limit in the next few months at night raids on the British cities, a campaign known as "the Blitz." The Luftwaffe's inability to prevail over the RAF meant postponing indefinitely Operation Sea Lion, being considered the first defeat of Germany in World War 2.