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
Test No. 6 so great that the Soviet Union ceased all assistance to China. Thus, the Number 6 test was indeed an independent endeavor, after the induced military and economic sanctions enacted by the superpowers at the time, the United States and the Soviet Union. Nevertheless, a comparison of other fission-to-fusion timespans may be instructive. The time between the U.S.'s first atomic test and its first hydrogen bomb test was 86 months, for the USSR it was 75 months, for the UK 66 months and later for France, 105 months. The goal of China was to produce a thermonuclear device of at least