and broadcasting equipment, soundproofing, ventilation and reinforcement. Meanwhile, by the summer of 1938 the War Office, Admiralty and Air Ministry had developed the concept of a Central War Room that would facilitate discussion and decision-making between the Chiefs of Staff of the armed forces. As ultimate authority lay with the civilian government the Cabinet, or a smaller War Cabinet, would require close access to senior military figures. This implied accommodation close to the armed forces' Central War Room. In May 1939 it was decided that the Cabinet would be housed within the Central War Room. In August 1939, with war imminent and protected government facilities in the suburbs not yet ready, the War Rooms became operational on 27 August 1939, only days before the invasion of Poland on 1 September, and Britain's declaration of war on Germany on 3 September. Wartime use During its operational life two of the Cabinet War Rooms were of particular importance. Once operational, the facility's Map Room was in constant use and manned around the clock by officers of the Royal Navy, British army and Royal Air Force. These officers were responsible for producing a daily intelligence summary for the King, Prime Minister and the military Chiefs of Staff. The other key room was the Cabinet Room. Until the opening of the Battle of France, which began on 10 May 1940, Prime Minister Neville Chamberlain's war cabinet met at the War Rooms only once, in October 1939. Following Winston Churchill's appointment as Prime Minister, Churchill visited the Cabinet Room in May 1940 and declared: 'This is the room from which I will direct the war'. In total 115 Cabinet meetings were held at the Cabinet War Rooms, the last on 28 March 1945, when the German V-weapon bombing campaign came to an end. 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'. Up to 5 feet (1.5 metres) thick, 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. While the usage of many of the War Rooms' individual rooms changed over the course of the war, the facility included dormitories for staff, private bedrooms for military officers and senior ministers, and