This decision was taken by a cabinet sub-committee on 8 January 1947, in response to apprehension of an American return to isolationism, fears that Britain might lose its great power status, and the actions by the United States to withdraw unilaterally from sharing of nuclear technology under the 1943 Quebec Agreement.

The first British atomic bomb was successfully tested in Operation Hurricane, during which it was detonated on board the frigate HMS Plym anchored off the Monte Bello Islands in Australia on 3 October 1952.

The project concluded with the delivery of the first of its Blue Danube atomic bombs to Bomber Command in November 1953, but British hopes of a renewed nuclear Special Relationship with the United States were frustrated.

[3] Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, developed a theoretical justification for the process, which they published in Nature in 1939.

[8] George Paget Thomson, at Imperial College London, and Mark Oliphant, an Australian physicist at the University of Birmingham, were tasked with carrying out a series of experiments on uranium.

Oliphant had delegated the task to two German refugee scientists, Rudolf Peierls and Frisch, who could not work on the university's secret projects like radar because they were enemy aliens and therefore lacked the necessary security clearance.

Sir John Anderson, the Lord President of the Council, became the minister responsible, and Wallace Akers from Imperial Chemical Industries (ICI) was appointed the director of Tube Alloys.

[18] In July 1940, Britain had offered to give the United States access to its scientific research,[19] and Cockcroft, as part of the Tizard Mission, briefed American scientists on British developments.

[23] On 30 July 1942, Anderson advised the Prime Minister, Winston Churchill, that: "We must face the fact that ... [our] pioneering work ... is a dwindling asset and that, unless we capitalise it quickly, we shall be outstripped.

The British considered the Quebec Agreement to be the best deal they could have struck under the circumstances, and the restrictions were the price they had to pay to obtain the technical information needed for a successful post-war nuclear weapons project.

[34][35] As overall head of the British Mission, Chadwick forged a close and successful partnership with Brigadier General Leslie R. Groves, the director of the Manhattan Project.

[39] On 8 August 1945 the Prime Minister, Clement Attlee, sent a message to President Harry Truman in which he referred to themselves as "heads of the Governments which have control of this great force".

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

Truman cabled on 20 April that he did not see the communiqué he had signed as obligating the United States to assist Britain in designing, constructing and operating an atomic energy plant.

[67] During the war, Chadwick, Cockcroft, Oliphant, Peierls, Harrie Massey and Herbert Skinner had met in Washington, D.C., in November 1944, and drawn up a proposal for a British atomic energy research establishment, which they had calculated would cost around £1.5 million.

Tube Alloys had performed much of the pioneering research on gaseous diffusion for uranium enrichment, and Oliphant's team in Berkeley were well-acquainted with the electromagnetic process.

His appointment as CSAR was announced on 1 January 1946, but Groves asked him to assist in the American Operation Crossroads nuclear tests at Bikini Atoll.

[94] The decision was publicly announced in the House of Commons on 12 May 1948 by the Minister of Defence, Albert Alexander, albeit in an oblique answer to a pre-arranged question from George Jeger, a Labour Party backbencher.

Meanwhile, because the adjustment applied retrospectively to VJ Day, it received reimbursement for the supplies allocated to the United States, thus easing Britain's dollar shortage.

Its growing size was the principal reason the Americans reopened the negotiations resulting in the Modus Vivendi,[107] which allowed for limited sharing of technical information between the United States, Britain and Canada.

The opposition of several key officials, including the United States Atomic Energy Commission's Lewis Strauss, and Senators Bourke B. Hickenlooper and Arthur Vandenberg, coupled with security concerns aroused by the 2 February 1950 arrest of Fuchs, who was working at Harwell, as a Soviet spy, caused the proposal to be rejected.

This would be used in BEPO, the experimental reactor built at Harwell, but the plant required uranium oxide feed, and the export of this from the United States was banned under the McMahon Act.

Similarly, while the Montreal Laboratory had experience with designing and building the ZEEP heavy-water reactor in Canada, no heavy water was available in the UK, so graphite was the only choice for a neutron moderator.

[142] Despite concerns over whether the process would work, numerous minor changes, and construction problems related to the steel used, the plant was completed on schedule in April 1951.

[153] The choice of plutonium for the fissile component of the bomb meant that Penney's HER team at Fort Halstead had to design an implosion-type nuclear weapon.

They considered how atomic bombing missions would be flown, and prepared training courses and manuals on how the production weapon, codenamed Blue Danube, would be stored, handled and maintained.

[165] A small fleet was assembled for Operation Hurricane that included the aircraft carrier HMS Campania, which served as the flagship, and the LSTs Narvik, Zeebrugge and Tracker, under the command of Rear Admiral A. D. Torlesse.

[167] It took Campania and Plym eight weeks to make the voyage, as they sailed around the Cape of Good Hope to avoid traversing the Suez Canal,[166] as there was unrest in Egypt at the time.

[183] On 5 November 1953, the Air and Naval Staffs therefore issued an Operational Requirement (OR1127) for a smaller, lighter atomic bomb capable of being carried by their English Electric Canberra, Gloster Javelin and Supermarine Scimitar aircraft.

[195] The successful British hydrogen bomb programme, and a favourable international relations climate caused by the Sputnik crisis, led to amendment of the United States Atomic Energy Act in 1958, and a resumption of the nuclear Special Relationship between America and Britain under the 1958 US–UK Mutual Defence Agreement.