Over in length, and with over of roads, the site was designed to accommodate the Prime Minister, the entire
Cabinet Office, other civil servants, and domestic support staff. Blast-proof and self-sufficient, the complex could accommodate up to 4,000 people in complete isolation from the outside world for up to three months. The underground city was equipped with all the facilities needed to survive: from hospitals, canteens, kitchens and laundries to storerooms for supplies, accommodation areas and offices. An underground lake and treatment plant could provide drinking water, and twelve tanks could store the fuel required to keep the four generators in the underground power station running for up to three months. The air within the complex could be kept at a constant humidity and heated to around . It was also equipped with the second-largest telephone exchange in Britain, a
BBC studio from which the PM could address the nation, and an internal
Lamson Tube system that could relay messages throughout the complex, using compressed air. To maintain the secrecy of the site, even during a countdown to war, it was envisaged that 4,000 essential workers would assemble at an outlying destination known as Check Point.
Warminster fulfilled this function, and from there a fleet of army lorries would have transported staff to the CGWHQ site. About 210 senior Whitehall officials and their staff, similarly unaware of their destination, were to assemble at
Kensington (Olympia) station on the
West London line, before setting off by special train for
Warminster, then a short trip by bus to
Warminster Infantry Training Centre. There they would be broken into small groups to conclude their journey with a lorry trip to Corsham. The Prime Minister was to remain at
Downing Street until the last moment, before being transported to Corsham by helicopter. The facility was divided into 22 areas. Some areas were repurposed over the years, but the allocation of space in 1981 was as follows: • Area 1: Air filtration plant (originally the
General Post Office area including the telephone exchange) • Area 2:
Royal Air Force Operations Centre (originally offices and dormitories for the
Board of Trade,
Her Majesty's Stationery Office, Office of Minister for Science and
Lord Chancellor's Department) • Area 3: Royal Air Force offices and dormitory • Area 4: Dormitory • Area 5: Dormitory and stores • Area 6: Kitchen and bakery • Area 7: Canteen • Area 8: Telephone exchange • Area 9: Hospital and stores (originally a dormitory) • Area 10:
Ministry of Transport offices • Area 11: Water treatment and stores • Area 12: Canteen and laundry • Area 13:
Ministry of Power and
Ministry of Agriculture offices and dormitory • Area 14: Prime Minister, War Cabinet, Cabinet Secretariat and Chiefs of Staff offices and dormitory • Area 15: Camp Commandant, Establishment offices and
Lamson room • Area 16:
Central Office of Information,
Ministry of Health,
Home Office, Ministry of Housing and Local Government and BBC studio • Area 17:
Ministry of Labour offices and "special accommodation" suites • Area 18: Admiralty, British Army and Ministry of Defence offices • Area 19: Workshops and power generation • Area 20: Stores • Area 21: Communications centre • Area 22: Foreign Office offices and dormitory In addition, there were water and fuel storage areas adjacent to the water treatment and power generation areas respectively, not officially numbered but sometimes referred to as Areas 23 and 24. ==Scheduled monuments==