Passive defence, involving measures taken by the public, was a key issue, and as early as 1924 the Committee of Imperial Defence had formed an Air Raid Precautions Sub-committee. Attack by hostile bomber aircraft was the prime concern. The most public result of civil defence measures was the September 1938 issue of gas masks to all members of the public in response to the Munich Crisis. The Munich Crisis was also the catalyst for large numbers of volunteers becoming involved in the organisation of air raid precautions by becoming wardens or joining first aid parties and rescue teams.
Throughout the summer the pace of civil defence preparations increased at government, local authority and individual level. On 1 September 1939 the first blackout, involving extinguishing all external and inessential lights and shielding essential interior and outside lamps, took place. The blackout marked Britain's clearest indication of civil defence and the imminence of war. Within minutes of Neville Chamberlain's announcement of hostilities on 3 September 1939 air raid sirens sounded throughout Britain, echoing peoples' fears of a massive and immediate blow from the air. Fortunately, it was a false alarm caused by an unidentified allied aircraft.
With the pressing fear of air attack ever present, attention was now given to how fires started by bombs could be dealt with. During the inter-war period fire services had been controlled by a multiplicity of local authorities. It was recognised that professional fire brigades would need reinforcement to meet the expected weight of attack. As a result, the Auxiliary Fire Service (AFS) was formed. Following the blitz on London and major cities across the UK between 1940 and 1941, it became apparent there had been instances of very poor working relations between professional fire brigades and the AFS, and the decision was taken to form a national fire service. This allowed the fire service to develop common doctrine, training and equipment as well as generally raising the standards of fire protection.
The bulk of the civil defence effort went into dealing with the threat of air raids. Each area had a number of Air Raid Precaution Wardens to monitor precautions (such as blackout restrictions) and make sure they were properly enforced. Local authorities and central government had to make provision for medical and rescue parties and look for all possible means of rescuing, transporting and treating casualties.
A civil defence measure that caused much distress on an individual level was evacuation. Evacuation took many forms; there was official evacuation of children and the sick to safe areas, evacuation of government business, and unofficial arrangements made by businesses and individuals to relocate without assistance from the government. Immediately before the outbreak of war, evacuation plans were put into motion, resulting in the evacuation of 1.5 million official evacuees (mostly children and the sick) between 1 and 3 September 1939. When the massive expected air raids did not occur, there was a drift back to individuals' hometowns. However, with the fall of France, the onset of the Battle of Britain and the threat of invasion, evacuation was put into practice once again. Children were even evacuated to the dominions, but the overseas evacuation scheme was halted in mid-1940 when two ships carrying evacuees were torpedoed with heavy loss of life.
Throughout the war the War Cabinet devoted much time working towards better civil defence. Discussions covered a wide variety of topics, from supplies of civil defence materials, to financing measures, to dealing with public apathy. Even conditions in a single public shelter did not escape attention, especially after Winston Churchill galvanised the government following his appointment as Prime Minister.