Old War Office Building

Old War Office Building

During the 1920s and 1930s, British civil servants and politicians, looking back at the performance of the state during World War I, concluded that there was a need for greater co-ordination between the three Services that made up the armed forces of the United Kingdom—the British Army, the Royal Navy, and the Royal Air Force. The formation of a united ministry of defence was rejected by David Lloyd George's coalition government in 1921; but the Chiefs of Staff Committee was formed in 1923, for the purposes of inter-Service co-ordination. As rearmament became a concern during the 1930s, Stanley Baldwin created the position of Minister for Coordination of Defence. Lord Chatfield held the post until the fall of Neville Chamberlain's government in 1940; his success was limited by his lack of control over the existing Service departments and his limited political influence.
Old War Office Building

Winston Churchill, on forming his government in (May) 1940, created the office of Minister of Defence to exercise ministerial control over the Chiefs of Staff Committee and to co-ordinate defence matters. The post was held by the Prime Minister of the day until Clement Attlee's government introduced the Ministry of Defence Act of 1946. The new ministry was headed by a Minister of Defence who possessed a seat in the Cabinet. The three existing service Ministers—the Secretary of State for War, the First Lord of the Admiralty, and the Secretary of State for Air—remained in direct operational control of their respective services, but ceased to attend Cabinet.

https://en.wikipedia.org/wiki/Ministry_of_Defence_(United_Kingdom)

https://en.wikipedia.org/wiki/Minister_for_Co-ordination_of_Defence

https://en.wikipedia.org/wiki/Thomas_Inskip,_1st_Viscount_Caldecote

https://en.wikipedia.org/wiki/First_Sea_Lord
https://en.wikipedia.org/wiki/Ernle_Chatfield,_1st_Baron_Chatfield .