The appearance of German bombers in the skies over London during the afternoon of September 7, 1940 heralded a tactical shift in Hitler's attempt to subdue Great Britain. During the previous two months, the Luftwaffe had targeted RAF airfields and radar stations for destruction in preparation for the German invasion of the island.
With invasion plans put on hold and eventually scrapped, Hitler turned his attention to destroying London in an attempt to demoralize the population and force the British to come to terms. At around 4:00 PM on that September 7th day, 348 German bombers escorted by 617 fighters blasted London until 6:00 PM. Two hours later, guided by the fires set by the first assault, a second group of raiders commenced another attack that lasted until 4:30 the following morning.
This was the beginning of the Blitz - a period of intense bombing of London and other cities that continued until the following May. For the next consecutive 76 days, London was bombed either during the day or night. Fires consumed many portions of the city. Residents sought shelter wherever they could find it - many fleeing to the Underground stations that sheltered as many as 177,000 people during the night. In the worst single incident, 450 were killed when a bomb destroyed a school being used as an air raid shelter. Londoners and the world were introduced to a new weapon of terror and destruction in the arsenal of twentieth century warfare.
The Blitz ended on May 11, 1941 - after 247 nights of bombing - when Hitler called off the raids in order to move his bombers east in preparation for Germany's invasion of Russia.