1958 US–UK Mutual Defence Agreement as an atomic spy, caused the proposal to be dropped. 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, reinforced the Americans' distrust of British security arrangements. The first British atomic bomb was successfully tested in Operation Hurricane on 3 October 1952, but although it was more advanced than the American bombs of 1946, Britain was still several years behind in nuclear weapons technology. The United States conducted Ivy Mike, the first nuclear test of a true thermonuclear device (also known as a hydrogen
British hydrogen bomb programme in 1949. The successful test of an atomic bomb represented an extraordinary scientific and technological achievement. Britain became the world's third nuclear power, reaffirming its status as a great power, but hopes that the United States would be sufficiently impressed to restore the Special Relationship were soon dashed. On 1 November 1952, the United States conducted Ivy Mike, the first successful test of a true thermonuclear device (also known as a hydrogen bomb). Due to its physical size and use of cryogenic liquid deuterium, it was not suitable for use as a deliverable weapon, but the Castle Bravo test on