After Hiroshima and Nagasaki revealed the existence of the atomic bomb to the world,
Labour Prime Minister Clement Attlee published a detailed account, prepared by his
Conservative predecessor
Winston Churchill, of the United Kingdom's participation in developing the bomb. On 8 August 1945 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". For the next year he attempted to persuade Truman to grant access to information which the British believed they deserved given their involvement.
The Americans disagreed. Manhattan Project head
Leslie Groves had excluded British scientists from participating in the manufacturing of the Hiroshima and Nagasaki bombs, contrary to the intentions of his government for close cooperation, for security reasons. Postwar spy scandals in both countries increased American concerns over atomic secrecy. More importantly, Truman hoped to establish international control over atomic weapons, and sharing information with even a close ally like Britain might have made such controls impossible. Nonetheless, the Americans' refusal to share information, formalised by the
McMahon Act of 1946 restricting foreign access to US nuclear technology, shocked and disappointed the British