1938 - Britain began work on a secret emergency working room for the Cabinet and the Chiefs of Staff in case of air attack. The old Board of Trade was an unusually strong building in a central location, with basement storage rooms that could be converted to war rooms. The area was finally strengthened against air attack in Dec. 1940 with steel beams and concrete pumps supplied by the United States.
1939 - The Cabinet War Rooms became operational on Sunday, August 27, only one week before the German invasion of Poland. The War Cabinet would have 115 meetings in the largest of the rooms during the war. The nerve center of the Rooms was the Map Room, manned 24 hours per day by officers of the Army, Navy, and RAF. Daily summaries were produced for the Chiefs of Staff and the PM. Naval convoys were charted with pins. The Annex room showed a giant map of Russia and the Eastern Front.
1940 - Churchill became Prime Minister May 10, but only met in the War Rooms occasionally until bombs damaged No. 10 Downing Street Oct. 15. After that, he would meet in the War Rooms on a regular basis. All clocks in the rooms today are set a 5 pm, when the War Cabinet met on Oct. 15. The BBC installed communications equipment in Room 60 that allowed Churchill to make radio broadcasts from his office-bedroom on four occasions, including his Sept. 11, 1940 speech warning of Hitler's plans.
1941 - The War Rooms expanded into the area known as the Courtyard Rooms, with bedrooms installed for Churchill's staff and his wife Clementine, and a dining room for both of them.
1943 - Bell Telephone installed the Sigsaly scrambler telephone in Selfridges Department store on Oxford Street, and an extension in the Cabinet War Rooms in a small room disguised as the PM's toilet.
1945 - The Cabinet War Rooms were officially closed Aug. 16.
1984 - The Imperial War Museum opened the rooms to public tours.
2001 - Additional rooms were opned to the public that had not been accessible in 1984, including the nine rooms of the Churchill suite.
2005 - The Churchill Museum opened in another restored section of the underground War Rooms.