Air Raid Precautions 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.
source:wikipedia\Image by: Watt_Dabney