The Ministry of Supply (MoS) was a department of the UK government formed on 1 August 1939 by the Ministry of Supply Act 1939 (2 & 3 Geo. 6. c. 38) to co-ordinate the supply of equipment to all three British armed forces, headed by the Minister of Supply. A separate ministry, however, was responsible for aircraft production, and the Admiralty retained responsibilities for supplying the Royal Navy. During the war years the MoS was based at Shell Mex House in The Strand, London.

The Ministry of Supply also took over all army research establishments in 1939. The Ministry of Aircraft Production was abolished in 1946, and the MoS took over its responsibilities for aircraft, including the associated research establishments. In the same year, it also took on increased responsibilities for atomic weapons, including the H-bomb development programme.

The Ministry of Supply was abolished in late 1959 and its responsibilities passed to the Ministry of Aviation, the War Office, and the Air Ministry. The latter two ministries were subsequently merged with the Admiralty to form the Ministry of Defence.

The Ministry of Supply instigated the Rainbow Codes designation system. This assigned projects a two-word codename, the first word being a colour and the second a noun. As a result, secret weapon projects—including numerous nuclear weapons—were given lighthearted names such as Green Cheese, Blue Slug or Red Duster.

The minister was assisted by the Parliamentary Secretary to the Ministry of Supply.

The Ministry of Supply was responsible for building and running the Royal Ordnance Factories, which produced explosives and propellants, filled ammunition, and constructed guns and rifles. However, the Ministry of Works and/or private building contractors acted as agents during their construction.

The ministry was also responsible for the supply of tanks and other armoured fighting vehicles. W. A. Robotham of Rolls-Royce was appointed chief engineer of tank design in the ministry in November 1941. He went on the 1942 tank mission to America. Most of the technicians in the Department of Tank Design in Ivy Bridge House had been recruited at the start of hostilities, and few had the experience to advise the industry design teams. They were spread over an "immense number" of projects, and lacked clear directives from the War Office general staff, so had no clear conception of their requirements. The answer in the ministry to reports of problems was to "shoot the messenger". Industry outsiders Robotham was dealing with had the attitude that he would be "gone tomorrow", so he resigned in August 1943. He thought (which turned out to be true) that any improvements would not reach the firing line before the end of the war.

Edward Brisch worked in the Department of Tank Design from 1942.