page_title: British hydrogen bomb programme
section_title: End of American cooperation
hierarchical_section_title: British hydrogen bomb programme / Background / End of American cooperation
caption_attribution_description: President Harry Truman and Rt. Hons. Clement Attlee and Mackenzie King boarding U.S.C.G. Sequoia for discussions about the atomic bomb
context_page_description: The British hydrogen bomb programme was the ultimately successful British effort to develop hydrogen bombs between 1952 and 1958.
  During the early part of the Second World War, Britain had a nuclear weapons project, codenamed Tube Alloys. At the Quebec Conference in August 1943, British prime minister Winston Churchill and United States president Franklin Roosevelt signed the Quebec Agreement, merging Tube Alloys into the American Manhattan Project, in which many of Britain's top scientists participated. The British government trusted that America would share nuclear technology, which it considered to be a joint discovery, but the United States Atomic Energy Act of 1946 ended technical cooperation.
  Fearing a resurgence of American isolationism, and the loss of Britain's great power status, the British government resumed its own development effort, which was codenamed "High Explosive Research".
  The successful nuclear test of a British atomic bomb in Operation Hurricane in October 1952 represented an extraordinary scientific and technological achievement.
context_section_description: With the end of the war the Special Relationship between Britain and the United States became, in the words of Margaret Gowing, "very much less special". The British government had trusted that America would share nuclear technology, which it considered a joint discovery. On 8 August 1945 the Prime Minister, Clement Attlee, sent a message to President Harry Truman in which he referred to both of them as "heads of the Governments which have control of this great force".
  On 9 November 1945, Attlee and the Prime Minister of Canada, Mackenzie King, went to Washington, D.C., to confer with Truman about future cooperation in nuclear weapons and nuclear power. A Memorandum of Intention they signed replaced the Quebec Agreement. The three leaders agreed that there would be full and effective cooperation on atomic energy, but British hopes were soon disappointed. The Atomic Energy Act of 1946 (McMahon Act), which was signed into law by Truman on 1 August 1946, ended technical cooperation. Its control of "restricted data" prevented the United States' allies from receiving any information.
  This partly resulted from the arrest for espionage of British physicist Alan Nunn May, who had worked in the Montreal Laboratory, in February 1946, while the legislation was being debated. It was but the first of a series of spy scandals. The arrest of Klaus Fuchs in January 1950, and the June 1951 defection of Donald Maclean, who had served as a British member of the Combined Policy Committee from January 1947 to August 1948, left Americans with a distrust of British security arrangements. The remaining British scientists working in the United States were denied access to papers that they had written just days before.
caption: President Harry Truman and prime ministers Clement Attlee and Mackenzie King boarding USS Sequoia for discussions about nuclear weapons, November 1945
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