A sandbag pillbox being constructed outside the New Public Offices, spring 1940 (H1584)

Work began in June 1938 on adapting these humble storage areas, ten feet below ground, to house the central core of government and a unique military information centre to serve the Prime Minister and the Chief of Staff of the air, naval and land forces. The events of the Munich crisis in the early autumn speeded up the process.

Seen by most planners as no more than temporary, the rooms were constructed under the watchful eye of Major-General Sir Hastings (later Lord) Ismay, assisted by Major (later Major-General Sir Leslie) Hollis, and became fully operational on 27 August 1939, exactly a week before the German invasion of Poland and Britain's declaration of war. This 'temporary' measure was to serve as the central shelter for government and the military strategists for the next six years.

VJ Day celebrations in London, 1945 (Keystone)

With the surrender of the Japanese forces in the Far East in August 1945, the Rooms were no longer needed and, on 16 August 1945, the lights in the Central Map Room were switched off for the very first time since the start of the war and the door was locked. This room, its annexe, Churchill's office-bedroom and the Cabinet Room were then left intact and undisturbed until an announcement in the Parliament in 1948 ensured their preservation as an historic site.

Restricted access was subsequently possible, but few were even aware of the existence of this previously top secret installation and it was only in 1981 when the Prime Minister, Margaret Thatcher, decided that the site should be made more easily accessible that its history became more widely known.

During the next three years the Imperial War Museum and the Department of the Environment arranged for the careful preservation and restoration of the complex and made the adaptations which were necessary to give visitors an intimate view of the contents of the Rooms and the routines of life in them.