During 1939 and the start of 1940 hardly any bombs were dropped on Britain. But Hitler planned to invade Britain. In September 1940 the German's started to bomb Britain's cities instead of RAF air bases hoping that Britons would panic and surrender. This period was known as The Blitz. As soon as the aircraft were spotted in the night sky, air raid sirens sounded to warn everyone that an air raid was coming. Some families would run down to a communal brick or concrete shelter in their street. Others sheltered from the bombs at home in their cellars or underneath a table or the stairs. Families with shelters in their gardens could hide in there. These were usually damp and dark and made from corrugated iron. they were known as Anderson shelters. In London they could shelter in the underground railway stations. At first this was very uncomfortable but as time went on bunk beds, toilets and snacks were provided. These stations were not totally safe in January 1941, a bomb fell above Bank underground station killing over 100 people who were sheltering below. Each street had an Air Raid Warden. Their job was to send for fire engines and ambulances, and to check for casualties or unexploded bombs.