On 15 September 1940, the Battle of Britain reached its climax. The Royal Air Force shot down 56 invading German aircraft in two dogfights. The costly raid convinced the German high command that the Luftwaffe could not achieve air supremacy over Britain, and the next day daylight attacks were replaced with night-time sorties as a concession of defeat.
It was obvious to both sides that German tactics had failed and the Luftwaffe had not gained the air supremacy they needed for an invasion. Fighting continued for another few weeks, but the action on 15 September was seen as an overwhelming and decisive defeat for the Luftwaffe. For this reason, this date is celebrated as Battle of Britain Day.