The treaty allowed American nuclear weapons to be supplied to Britain through Project E for use by the Royal Air Force and British Army of the Rhine until the early 1990s when the UK became fully independent in designing and manufacturing its own warheads.

The treaty provided for the sale to the UK of one complete nuclear submarine propulsion plant, as well as ten years' supply of enriched uranium to fuel it.

[2] At the Quadrant Conference in August 1943, the Prime Minister of the United Kingdom, Winston Churchill, and the President of the United States, Franklin Roosevelt, signed the Quebec Agreement, which merged Tube Alloys with the American Manhattan Project to create a combined British, American and Canadian project.

[5] The September 1944 Hyde Park Aide-Mémoire extended both commercial and military co-operation into the post-war period,[6] but Roosevelt died on 12 April 1945, and it was not binding on subsequent administrations.

When Field Marshal Sir Henry Maitland Wilson raised the matter in a Combined Policy Committee meeting in June 1945, the American copy could not be found.

[9] On 8 August, the Prime Minister, Clement Attlee, sent a message to President Harry Truman that referred to themselves as "heads of the Governments which have control of this great force".

[12][13] A Memorandum of Intention was signed on 16 November 1945 that made Canada a full partner and replaced the Quebec Agreement's requirement for "mutual consent" before using nuclear weapons to one for "prior consultation".

[18] Fearing a resurgence of American isolationism and Britain losing its great power status, the British government restarted its own development effort,[19] now codenamed High Explosive Research.

[35] On 1 November, the United States conducted Ivy Mike, the first nuclear test of a true thermonuclear device (also known as a hydrogen bomb).

[37] That prompted President Dwight Eisenhower, who was inaugurated in January 1953, to inform the US Congress that the McMahon Act, which he considered a "terrible piece of legislation" and "one of the most deplorable incidents in American history of which he personally felt ashamed", was obsolete.

[39] At the three-power Bermuda Conference in December 1953, Eisenhower and Churchill,[40] who had become prime minister again on 25 October 1951,[41] discussed the possibility of the United States giving Britain access to American nuclear weapons in wartime,[40] which came to be called Project E.[39] There were technical and legal issues that had to be overcome before American bombs could be carried in British aircraft.

[44] On 13 June 1956, another agreement was concluded for the transfer of nuclear submarine propulsion technology to Britain, which saved the British government millions of pounds in research and development costs.

It precipitated a row with the JCAE over whether that was permitted under the Atomic Energy Act of 1954 and whether Britain met the security standards set by the 1955 agreement.

[46] Eisenhower met with the new British prime minister, Harold Macmillan, in Bermuda in March 1957 and raised the possibility of basing US intermediate range ballistic missile (IRBM) systems in the UK.

[48] There were also discussions on exchanging nuclear submarine propulsion technology for information on the British Calder Hall nuclear power plant, allowing the United Kingdom Atomic Energy Authority (UKAEA) to purchase uranium ore from Canada and co-ordinating the war plans of RAF Bomber Command with those of the Strategic Air Command.

[50] The British hydrogen bomb programme attempted to detonate a thermonuclear device in the Operation Grapple test series at Christmas Island in the Pacific.

In the widespread calls for action in response to the Sputnik crisis, officials in the United States and Britain seized an opportunity to mend their relationship.

[60] He immediately sensed how shaken the Americans had been by Sputnik,[55] which placed the Eisenhower administration under great public pressure to act on the deployment of IRBMs by a shocked and distraught nation.

By October 1957, its head, Rear Admiral Hyman G. Rickover, felt that their questions were slowing the deployment of the Polaris submarine-launched IRBM at a critical time.

[65] That could save millions of pounds and avoid domestic political complications if Britain had to persist with nuclear testing during an international moratorium.

Quarles and Major General Herbert Loper, the Assistant to the Secretary of Defense for Atomic Energy Affairs, were forced to deal with pointed questions about nuclear proliferation.

[71] British information security, or the lack thereof no longer seemed so important now that the Soviet Union was apparently ahead and the UK had independently developed the hydrogen bomb,[72] but the JCAE objected to the terms of the proposed deal to trade British uranium-235 for US plutonium under which the US would pay USD$30 per gram for plutonium that cost $12 per gram to produce in the UK.

[73] The amendments were passed by the US House of Representatives on 19 June but not without changes that now limited exchanges of nuclear weapons data to nations that had made substantial progress in the field.

[77] The agreement enables the US and the UK to exchange classified information with the objective of improving each party's "atomic weapon design, development, and fabrication capability".

[81] Article 3 provided for the sale to the UK of one complete nuclear submarine propulsion plant, as well as the uranium needed to fuel it for ten years.

It was amended on 7 May 1959 to give Britain access to non-nuclear components[77] and to permit the transfer of special nuclear material such as plutonium, HEU and tritium.

The AEC invited the British government to send representatives to a series of meetings in Washington, DC, on 27 and 28 August 1958 to work out the details.

[111] Subjects investigated includedone-point safety, computer codes, metallurgy and fabrication technology for beryllium, uranium and plutonium, corrosion of uranium in the presence of water and water vapour, underground effects tests, outer-space testing, clandestine testing, the technology of lithium compounds, high explosives, deuterium monitors, extinguishing plutonium fires, high-speed cameras, mechanical safing, liquid and solid explosive shock initiation, environmental sensing switches, neutron sources, tritium reservoirs, telemetry, hydrodynamic and shock relations for problems with spherical and cylindrical symmetry, nuclear cross sections, radiochemistry, atomic demolition munitions, warhead hardening, asymmetric detonations, terrorist nuclear threat response, nuclear weapons accidents and waste management.

The Anglo-American special relationship proved mutually beneficial although it has never been one of equals after the World Wars since the US has been far larger than the United Kingdom both militarily and economically.

[118][119] On 25 July 2024, with the treaty about to expire, the UK government proposed amendments that included removal of the expiry date for the transfer of special nuclear materials and equipment, thereby allowing the agreement to remain in force on an "enduring basis".