The Ministry of Defence was a department of the British Government responsible for defence and the British Armed Forces.
Prior to the Second World War defence policy was co-ordinated by the Committee of Imperial Defence (CID). In 1936 the post of Minister for Co-ordination of Defence was established, though he did not have a department and the political heads of the three services—the First Lord of the Admiralty for the Royal Navy, the Secretary of State for War for the Army and the Secretary of State for Air for the Royal Air Force—continued to attend Cabinet.
On the outbreak of war in 1939 the CID was suspended and on 3 April 1940 the office of Minister for Co-ordination of Defence was abolished. When Winston Churchill became Prime Minister in May 1940 he personally assumed responsibility for inter-service co-ordination, with the title of Minister of Defence, and the heads of the three services were not included in the War Cabinet. The Minister had few departments, the most famous of which was MD1 which allowed unusual ideas for weapons to be developed under the patronage of Churchill with less interference from the services and got the nickname "Churchill's Toyshop".
After the end of the war in Europe in May 1945 the First Lord and the Secretaries for War and Air rejoined the Cabinet, though the Prime Minister remained Minister of Defence.
The suspension of the CID was made permanent by a White Paper (Cmd. 6923) in 1946, and from 4 October that year the service chiefs were no longer in the Cabinet. The former First Lord of the Admiralty A.V. Alexander was appointed Minister of Defence on 20 December 1946 and the Ministry of Defence was formally established on 1 January 1947 by the Ministry of Defence Act 1946. The Ministry was responsible for liaising between the individual service ministries and co-ordinating defence policy.
Under the Defence (Transfer of Functions) Act 1964 the Ministry of Defence was merged with the Admiralty, the War Office and the Air Ministry to form the current Ministry of Defence on 1 April 1964; the Minister of Defence became Secretary of State for Defence.
Ministers of Defence, 1940–1964
- 10 May 1940: Winston Churchill, also Prime Minister
- 27 July 1945: Clement Attlee, also Prime Minister
- 20 December 1946: A.V. Alexander (created Viscount Alexander of Hillsborough on 27 January 1950)
- 28 February 1950: Emanuel Shinwell
- 28 October 1951: Winston Churchill, also Prime Minister
- 1 March 1952: The Viscount Alexander of Tunis (created Earl Alexander of Tunis on 14 March 1952)
- 18 October 1954: Harold Macmillan
- 7 April 1955: Selwyn Lloyd
- 20 December 1955: Sir Walter Monckton
- 18 October 1956: Antony Head
- 13 January 1957: Duncan Sandys
- 14 October 1959: Harold Watkinson
- 13 July 1962: Peter Thorneycroft
Permanent Secretaries to the Ministry of Defence, 1947–1964
- 1947: Sir Henry Wilson Smith
- 1948: Sir Harold Parker
- 1956: Sir Richard Powell
- 1960: Sir Edward Playfair
- 1961: Sir Robert Scott
- 1964: Sir Henry Hardman
Parliamentary Secretaries to the Ministry of Defence, 1952–1964
- 28 February 1952: Nigel Birch
- 18 October 1954: The Lord Carrington
- 26 May 1956: The Earl of Gosford
- 18 January 1957: The Lord Mancroft
- 11 June 1957: office vacant.