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 1 March 1954 used a much smaller device with solid lithium deuteride . Boosted by the nuclear fusion reaction in lithium-7 , the yield of was more than twice what had been expected , and indeed was the largest detonation the Americans would ever carry out . This resulted in widespread radioactive fallout that affected 28 Americans , 236 Marshall Islanders , and the 23 crewmen of a Japanese fishing boat , the '' Daigo Fukuryū Maru '' ( '' Lucky Dragon No. 5 '' ) . Meanwhile , the Soviet Union tested Joe 4 , a boosted fission weapon with a yield of on 12 August 1953 . This was followed by Joe 19 , a true two-stage thermonuclear weapon on 20 November 1954
Ivy Mike
Ivy Mike
British hydrogen bomb programme