Construction of the Cabinet War Rooms, located beneath the Treasury building in the Whitehall area of Westminster, began in 1938.

[3] Pending this dispersal, in March 1938 Sir Hastings Ismay, then Deputy Secretary of the Committee of Imperial Defence, ordered an Office of Works survey of Whitehall to identify a suitable site for a temporary emergency government centre for use during bombing raids.

[4] Staff accessed the War Rooms via the main entrance of the NPO, and once inside the building, descended down Staircase 15, entering near to the Churchills' kitchen.

These officers were responsible for producing a daily intelligence summary for the King, Prime Minister and the military Chiefs of Staff.

[18] On 22 October 1940, during the Blitz bombing campaign against Britain, it was decided to increase the protection of the Cabinet War Rooms by the installation of a massive layer of concrete known as 'the Slab'.

[19] Up to 5 feet (1.5 metres) thick,[13] the Slab was progressively extended and by spring 1941 the increased protection had enabled the Cabinet War Rooms to expand to three times their original size.

From 1943, a SIGSALY code-scrambling encrypted telephone was installed in the basement of Selfridges, Oxford Street connected to a similar terminal in the Pentagon building.

[22] This enabled Churchill to speak securely with American President Roosevelt in Washington, with the first conference taking place on 15 July 1943.

[28] Below the level of the Cabinet War Rooms, a further sub-basement nicknamed "the Dock" was provided for staff members to sleep, so that they didn't have to make their way home through heavy air raids at the end of their shifts.

The ventilation system rattled throughout the night, mice were common, occupants had to stoop due to low ceilings, and there were no flushing toilets, only chemical ones.

[32] Even so, a tour was organised for journalists on 17 March, with members of the press being welcomed by Lord Ismay and shown around the Rooms by their custodian, Mr. George Rance.

Meanwhile, the atmospheric conditions of the site, being dry and dusty, were having a detrimental effect on the rooms' furnishings and historic maps and other documents.

[nb 2] In 1981, Prime Minister Margaret Thatcher, known as an admirer of Winston Churchill, expressed the hope that the Rooms could be opened before the next general election.

[38] Intended to act as a 'beacon' for the museum,[39] the new external design included a faceted bronze entranceway, and the interior showed the cleaned and restored Portland stone walls of the Treasury building and Clive Steps.

The museum makes extensive use of audiovisual technology, with the centrepiece being a 15-metre (50 ft) interactive table that enables visitors to access digitised material, particularly from the Churchill Archives Centre.

[42][nb 3] The museum is set out in chronological chunks, beginning with Churchill's appointment as Prime Minister in 1940 and going up to the end of his life in 1965 before starting again with his childhood and returning to May 1940.