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The Battle of Britain was a military campaign of the Second World War, in which the Royal Air Force (RAF) defended the United Kingdom (UK) against large-scale attacks by Nazi Germany's air force, the Luftwaffe. It has been described as the first major military campaign fought entirely by air forces. The British officially recognise the battle's duration as being from 10 July until 31 October 1940, which overlaps the period of large-scale night attacks known as The Blitz, that lasted from 7 September 1940 to 11 May 1941. German historians do not accept this subdivision and regard the Luftschlacht um England (Air Battle for England) as a single campaign lasting from July 1940 to June 1941, including the Blitz.

The Kanalkampf (Channel fight) was the German term for air operations by the Luftwaffe against the British Royal Air Force (RAF) over the English Channel in July 1940. The air operations over the channel began the Battle of Britain during the Second World War. By 25 June, the Allies had been defeated in Western Europe and Scandinavia. Britain rejected peace overtures and on 16 July, Adolf Hitler issued Directive 16 to the Wehrmacht (German armed forces), ordering preparations for the invasion of Britain, under the codename Unternehmen Seelöwe (Operation Sea Lion).

The Germans needed air superiority over southern England before the invasion and the Luftwaffe was to destroy the RAF, assume command of the skies and protect the cross-channel invasion from the Royal Navy. To engage RAF Fighter Command, the Luftwaffe attacked convoys in the English Channel. ... British and German writers and historians acknowledge that air battles were fought over the Channel between the Battle of France and Battle of Britain; deliberate German attacks against British coastal targets and convoys began on 4 July. During the Kanalkampf, the Luftwaffe received modest support from shore artillery and the E-Boats of the Kriegsmarine (German navy).

Fighter Command could not protect adequately the convoys; the Germans sank several British and neutral ships and shot down a considerable number of British fighters. The Royal Navy was forced to suspend the sailing of large convoys in Channel waters and close it to ocean-going vessels until more protection could be arranged, which took several weeks. On 1 August, Hitler issued Directive 17, extending Luftwaffe operations to the British mainland and RAF-related targets and on Adlertag (Eagle Day, 13 August) the main air offensive against the RAF began. The Kanalkampf had drawn out Fighter Command as intended and convoy attacks continued for several more days. Both sides had suffered losses but the Luftwaffe failed to inflict a decisive defeat on Fighter Command and the RAF; the Luftwaffe had yet to gain air superiority for Operation Sea Lion.

Directive 17, August 1, 1940, Battle of Britain, Full text .
https://en.wikipedia.org/wiki/List_of_Adolf_Hitler%27s_directives .

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