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Dunkirk evacuation -

The Dunkirk evacuation in May and June of 1940 and the defeat of France by Germany emboldened the Nazis to start planning an invasion of Great Britain.

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Attack imminent -

As early as May 1940, Prime Minister Winston Churchill believed a German attack was imminent. On June 18, in a famous speech to the House of Commons, he warned that the Battle of Britain was about to begin. "Let us therefore brace ourselves to our duties," he continued, "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.'"

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Hitler eyes England -

In the wake of France's capitulation, Adolf Hitler was sure the British government would agree to a compromise peace on the favorable terms he was prepared to offer. But as the Führer and the Nazi hierarchy gathered at Calais to peer across the Straits of Dover, Churchill's determination to continue the war became ever more evident.

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Plan of attack -

On July 16, Hitler ordered the preparation of Operation Sea Lion, the invasion of England. Hermann Göring's Luftwaffe was tasked with disabling Britain's naval capacity and driving the Royal Air Force (RAF) out of the sky.

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The bombing begins -

The following day, the Luftwaffe increased its bombing attacks on British shipping while carrying out numerous sorties on coastal airfields and other RAF facilities.

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"Eagle Day" -

On August 13, Hitler ordered the main offensive, called Adlertag (Eagle Day). Attacks moved inland, concentrating on airfields and communications centers. The Luftwaffe also began targeting aircraft factories.

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Britain responds -

RAF Fighter Command offered stiff resistance, but, with only 600 frontline fighters available, the effort severely strained resources.

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Numerically superior -

In contrast, the Luftwaffe was the largest and most formidable air force in the world. Three air fleets (Luftflotte) were made available consisting of about 1,300 bombers and dive-bombers and roughly 900 single-engine and 300 twin-engine fighters.

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Dynamic duo -

The RAF, however, had at its disposal two of the best fighter aircraft in the world—the Hawker Hurricane and the Supermarine Spitfire.

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Air supremacy -

The iconic Spitfire was renowned for its speed, excellent maneuverability, and impressive firepower. The Hurricane was equally formidable. It was the first RAF aircraft to fly over 300 mph (482 km/h) and was a reliable workhorse. In fact, it accounted for over 60% of the air victories in the Battle of Britain.

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Premier fighter -

The Luftwaffe's premier fighter was the Messerschmitt Bf 109. It was Germany's most important single-seater fighter plane throughout the Second World War.

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Aerial combat -

While numerically superior, German bombers such as the Heinkel He 111 and Junkers Ju 88 lacked bombload capacity to strike permanently devastating blows. And it quickly became apparent that they were vulnerable to British fighters, at least during daylight hours.

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Dogfights -

Throughout August 1940, dogfights over the English Channel were commonplace. On August 16, the Germans carried out assaults over Kent and the Thames Estuary, Sussex, and Hampshire, and at points near Harwich and the Isle of Wight. Fighter Command was taking a bruising.

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Losses mount up -

But the Germans suffered for their efforts. By late August, the Luftwaffe had lost more than 600 aircraft; the RAF, only 260.

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Group Operations Room -

The Battle of Britain was coordinated out of RAF Uxbridge where the No. 11 (Fighter) Group Operations Room was housed. Besides this military campaign, the Operations Room was  responsible for controlling fighter operations in the South East and occupied Europe throughout the Second World War, including during the Dunkirk evacuations and the Normandy landings.

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Scanning the skies -

Even before the Battle of Britain, the British had developed a highly efficient air defense network. Radar gave early warning of Luftwaffe raids, which were also tracked by the Observer Corps.

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The Dowding system -

The British were using the Dowding system, the world's first wide-area ground-controlled interception network. Named for Fighter Command's Commander-in-Chief Sir Hugh Dowding, it brought together technology such as radar, ground defenses, and fighter aircraft into a unified system of defense across the entire United Kingdom.

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The radar revolution -

Radar (radio detection and ranging) revolutionized British offensive and defensive capability throughout the Second World War, playing a vital role in locating incoming German bomber formations.

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The work of the WAAF -

The Battle of Britain saw members of  the Women's Auxiliary Air Force (WAAF) serve as radar operators and as plotters, tracking raids in the group and sector operations rooms. They also tested aerial guns after repair and operated barrage balloon sites, among other duties.

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A dark day -

Britain's darkest day of the campaign occurred on August 31, when 39 aircraft were shot down and 14 pilots killed. RAF sector stations were attacked, including RAF Biggin Hill, one of the principal fighter bases protecting London and South East England.

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The Blitz -

On September 7, the Germans launched a sustained attack on London. Fighter Command refocused its efforts on defending the capital from what became known as The Blitz.

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London targeted -

The skies above the city became an arena for dogfights as German fighters escorted bombers making wave after wave of bombing runs over London's docks, oil storage depots, gasworks, power stations, and other vital infrastructure.

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The city suffers -

Civilian casualty rates were high, particularly in the heavily populated streets of London's East End.

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Turning point -

The decision by the Germans to bomb London and other cities away from RAF targets proved a tactical error. Fighter Command was able to regroup, refuel, and rearm. It was the turning point in the Battle of Britain.

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Commanding the skies -

On September 15, the RAF, back to full operational capacity, finally succeeded in denying the Luftwaffe the air supremacy it needed in order to launch an invasion.

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September 15, 1940 -

On that day, the Germans suffered their highest losses since August 18  and it was clear the Luftwaffe had suffered an overwhelming and decisive defeat. The Battle of Britain was over.

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The Blitz continues -

The Second World War, however, was far from over. Over the next eight months, London was systematically bombed by the Luftwaffe for 56 of the following 57 days and nights.

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High casualty rate -

Across Britain, around 43,000 civilians were killed during the Blitz. In London alone, almost 30,000 perished.

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Iconic image -

Both sides lost heavily during the Battle of Britain. The Luftwaffe counted 2,662 pilots and aircrew dead. British losses amounted to 1,497, with Polish and Canadian pilots among the dead. One of those from Fighter Command killed was Pilot Officer Keith Gillman. He failed to return from combat over the English Channel on August 25, 1940, and was one of the first pilots lost in the campaign. This photo of him was used on the front cover of Picture Post and posthumously became the iconic image of a Battle of Britain pilot.

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Victoria Cross -

Another name synonymous with the campaign is Flight Lieutenant James Nicolson (1917–1945). He was the only Battle of Britain pilot and the only pilot of RAF Fighter Command to be awarded the Victoria Cross during the Second World War.

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"The Few" -

Shortly after the Battle of Britain was concluded, a poster was designed commemorating the pilots and aircrew. It contained Winston Churchill's famous lines, "Never was so much owed by so many to so few." Pilots who fought in the Battle of Britain have been known as "the Few" ever since, at times being specifically commemorated for Battle of Britain Day, on September 15. 

Sources: (RAF Museum) (Imperial War Museums) (Britannica) (Battle of Britain Diary) (International Churchill Society) 

See also: Lesser-known facts about World War II

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