Part II : 1950 -1957
 Thermonuclear research began in the 1930s with the hypothesis that thermonuclear reactions are the energy sources of the Sun and stars. The nuclei of deuterium (heavy hydrogen) react more easily than the nuclei of normal hydrogen, and after Harold Urey separated deuterium in 1931, interest in the possibility of reacting deuterium increased. In 1942, Edward Teller began working on the possibility of initiating such reactions by means of an atomic explosion, but his initial conclusion was negative. Later the year, he attended a conference on thermonuclear reactions where the group agreed that tritium (isotope of hydrogen) should be studied as well as deuterium and concluded that a thermonuclear explosion could be accomplished. The following year, plans for research on thermonuclear reactions were put aside at the newly formed Los Alamos laboratory to concentrate on uranium fission. Teller and a few others, however, continued their research.1
Until 1948, thermonuclear research received little support. Robert Oppenheimer, an early supporter, became opposed to further research on thermonuclear reactions after Hiroshima. Following the announcement that Russia had exploded an atomic bomb, the general advisory committee of the Atomic Energy Commission, chaired by Oppenheimer, recommended against proceeding with the development of a hydrogen bomb on technical, political, and moral grounds. The committee felt that the H-bomb was not yet technically feasible or economical and that lack of restrictions would mean high danger to civilization. This position was unpopular with many scientists at Los Alamos, where work continued, and with politicians, who recommended to President Truman that H-bomb development be initiated. The final catalyst appears to have been Klaus Fuchs's treachery; four days after he confessed to having given U.S. atomic secrets to the Russians, Truman directed that development of the H-bomb start.
With the presidential go-ahead in January 1950, Teller and associates at Los Alamos intensified their efforts to design a practical bomb and began preparations for some critical tests. Hydrogen liquefiers were needed for these, and Herrick L. Johnston of Ohio State University became a key figure in setting up and operating the equipment.