Air Raid Precautions (ARP) was an organisation in the United Kingdom set up as an aid in the prelude to the Second World War dedicated to the protection of civilians from the danger of air-raids. It was created in 1924 as a response to the fears about the growing threat from the development of bomber aircraft. Giulio Douhet had published his influential Command of the Air in 1921 and his main thesis had been memorably taken into English as "the bomber will always get through". Many of the practices and ideals set forth by the ARP lived on beyond the War through Civil Defence during the Cold war and still exist today in civilian organizations in the United Kingdom and the United States.

The bombing of Britain in the First World War began on 19 January 1915 when zeppelins dropped bombs on the Great Yarmouth area, killing six people. German bombing operations of the First World War were surprisingly effective, especially after the Gotha bombers surpassed the zeppelins. The most devastating raids inflicted 121 casualties for each ton of bombs dropped and it was this figure that was used as a basis for predictions. The 1924 ARP Committee produced figures estimating that in London there would be 9,000 casualties in the first two days and then a continuing rate of 17,500 casualties a week. These rates were thought conservative.

It was believed that there would be "total chaos and panic" and hysterical neurosis as the people of London would try to flee the city. To control the population harsh measures were proposed—bringing London under almost military control; physically cordoning London with 120,000 troops to force people back to work. A different government department proposed setting up camps for refugees for a few days before sending them back to London.

These schemes remained on paper only and while estimates of potential damage remained high, the Air Raids Commandant (Major General H. Pritchard of the Royal Engineers) favoured a more reasoned solution. He discerned that panic and flight were basically problems of morale, if the people could be organised, trained and provided with protection then they would not panic. As part of this scheme the country was divided into regions each having its own command and control structure, in potentia at least.

The 1924 estimates were, during the build up to the Second World War, regularly revised upwards, particularly in the light of the 1937 German bombing of Guernica, Spain. In 1938 the Air Ministry predicted 65,000 casualties a week—in the first month of war the British government was expecting a million casualties, three million refugees, and the majority of the capital destroyed. Measures to control this devastation were largely limited to grisly discussions about body disposal and the distribution of over a million burial forms to local authorities. In the same year the Socialist biologist JBS Haldane wrote a book titled A.R.P. (Air Raid Precautions) addressed to "the ordinary citizen, the sort of man and woman who is going to be killed if Britain is raided again from the air" and intended it to be a scientific counterbalance to the "propaganda" that comprised the majority of existing literature at the time. In the book, Haldane strongly criticises the measures taken by the government based on his professional knowledge of human physiology combined with his front-line experiences in the Spanish Civil War.

At the outbreak of the war the British government knew that air attacks would be a main part of the German war tactics so they ordered a million coffins after war was declared.The 1939 Hailey Conference had decided that providing deep shelters would lead to workers staying underground rather than working. This policy was reversed in 1940 when 79 tube stations opened for use as overnight shelters and specialised deep shelter construction begun.