On 15 September 1940, during the Second World War, an air battle was fought on 15 September 1940 during the Battle of Britain between the German Luftwaffe and British Royal Air Force (RAF). Now celebrated as Battle of Britain Day, on that date, the Luftwaffe launched its largest and most concentrated attack against London in order to out the RAF into a battle of annihilation. The German objective was to gain air superiority over the English Channel and allow the invasion of England, Operation Sea Lion, to proceed.