By 1935, British officials were discussing air raid precautions. Little was done, though, until the crisis of 1938, when many European countries were alarmed by Germany's behaviour towards Czechoslovakia. In Britain there was panic as people were afraid of bombing attacks. Evacuation plans were hastily announced; anti-aircraft guns were set up; and deep trenches were dug in London parks to serve as air raid shelters. The crisis ended after talks in Munich but it had shown that British civil defence was weak.

One result of the crisis was the fast development of air raid precautions (A.R.P.) under the leadership of Sir John Anderson. Spending on A.R.P. rose from £9.5 million in 1937-38 to £51 million in 1939-40.

Experts said that bombing would kill hundreds of thousands of people. So new plans were made for mass evacuation, the construction of large public shelters, and the erection of small units in private gardens ("Anderson" shelters) and inside houses ("Morrison" shelters).

Although the War began in September 1939, bombing of Britain did not start immediately. People developed a false sense of security and were not keen to have shelters. Once heavy bombing began, from the summer of 1940 onwards, shelters became more popular. Railway arches and basements were also used and, in London, people slept at night in the Underground Stations and tunnels.

The shelters - big and small - saved the lives of very many people, but there were deaths when large bombs fell directly on shelters. In some cases, many people were killed at once - for example, 64 died at Balham Underground Station when it took a direct hit on 15 October 1940.

Late in the War, in 1944 and 1945, the German flying bombs and V 2 rockets were new dangers that caused many deaths.

By the end of the War, German bombing had killed just over 60,000 people in Britain. The experts had over-estimated the strength of the German air force, and the amount of bombs that it could drop. However, many more would have died if shelters had not been provided.