Nuclear weapons are of two basic types. Atomic, or fission, bombs, such as those used in World War II, split uranium and plutonium atoms. Hydrogen, or thermonuclear, bombs fuse hydrogen isotopes. Edward Teller and Enrico Fermi conducted the first studies of a hydrogen bomb in 1942. Teller and Fermi believed that atoms of deuterium, an isotope of hydrogen, could be fused into helium with a simultaneous release of energy. Because such a process required stellar temperatures, then unobtainable on earth, Teller originally doubted that a hydrogen bomb could be built.
Despite his original doubts, Teller continued to study thermonuclear reactions and became increasingly convinced that a hydrogen bomb was possible. Although the United States would concentrate its World War II nuclear efforts on building fission bombs at Los Alamos, Teller and a small group of scientists conducted elementary research on the hydrogen bomb while working at Los Alamos. In particular, Teller and his colleagues found that much less deuterium and tritium would be required than originally thought, thereby making a hydrogen bomb more realistic.
With the end of World War II, the whole country, including Los Alamos, demobilized. Los Alamos faced severe shortages of manpower as senior scientists returned to their prewar university positions and younger staff left to enter graduate school. As a result, very little research and development on the hydrogen bomb took place. Among the technical accomplishments during the late 1940s, however, were the improvement of fission devices, the use of computers and computational modeling, and development of cryogenic technology to produce liquid deuterium fuel.
The ultimate success of the United States' thermonuclear program rested on five factors. First, was the discovery of a method to overcome the fundamental problem that thermonuclear systems lose as much energy as they create. Second, Los Alamos had to significantly increase the size of its scientific staff. The hydrogen bomb problem required complex interactions among physicists, chemists, and metallurgists. Third, to start a thermonuclear fire, smaller and more efficient fission bombs were needed. Fourth, computational ability had to be greatly enhanced. And fifth, the political decision had to be made to marshal the resources necessary to accomplish the task.
Because hydrogen bombs require stellar temperatures to ignite the thermonuclear fuel, the only possible way to ignite a hydrogen bomb was by using an atomic bomb. For the development of the hydrogen bomb to go forward, fission weapons had to be improved. The two wartime fission devices, Fat Man and Little Boy, were crude prototypes not capable of being adapted for use in a hydrogen bomb. A new class of fission bombs had to be designed, built, and tested. This process took years. The first testing of new fission devices did not take place until 1948, with more design improvements following in 1950.
Shortly after President Truman's directive to proceed with the hydrogen bomb program in January 1950, research began to bear fruit. Edward Teller and Stanislaw Ulam came up with a promising design, involving radiation implosion, which was translated by Richard Garwin into a working design. Once the design concept was reviewed and approved, work began on constructing the Mike device and planning for a full-scale test at the Pacific Proving Ground in the Marshall Islands.
The test of the Mike device was scheduled as part of the Operation Ivy test series, to be conducted in the fall of 1952 at Enewetak Atoll in the Marshall Islands. The Mike device was constructed on the remote island of Elugelap, located in the northern part of the atoll. Mike was not a bomb in the combat sense of the word. As ultimately constructed, it stood three stories tall, weighed over one million pounds, and used liquid deuterium, a cryogenic fuel. On October 31, 1952 (local time), after the entire atoll had been evacuated, Mike exploded with a yield of 10.4 megatons. The fireball was estimated to be over three miles in diameter. The island of Elugelap disappeared as did portions of other nearby islands. The successful test of Mike ushered in the era of multi-megaton nuclear weapons.