"Mike", the code name given to the first test of a hydrogen device that would trigger thermonuclear fusion, was the brainchild of physicist Edward Teller and mathematician Stanislaw Ulam. Conceived soon after the end of World War II, "Mike" was designed as a laboratory experiment, not a weapon. Its 10-megaton explosion, however, was almost 700 times more powerful than the fission bomb that devastated the Japanese city of Hiroshima, and more than 450 times more powerful than the bomb that exploded over Nagasaki. The "Mike" device effectively vaporized its island test site, leaving behind only a mile-wide crater.

Teller and Ulam's superbomb concept used a small fission bomb to trigger nuclear fusion. Its explosion provided the intense heat -- millions of degrees Celsius -- and high pressure needed to make the hydrogen-rich fuel undergo nuclear fusion, a process that forces atomic nuclei together and releases significantly more energy per unit of mass than is released in fission. The fuel used in the fusion device test was liquid deuterium. Deuterium is a form, or isotope, of hydrogen whose nuclei each contain one proton and one neutron. (Tritium is another fusable hydrogen isotope.) "Mike's" design concept is largely the same one used in today's fusion-based weaponry.

Following "Mike", the world altered its course from the peaceful path it had been on -- concluding a world war -- to a more dangerous one. Just as the test demonstrated the boundless power of fusion bombs (also called H-bombs and thermonuclear bombs), it highlighted the limited power of fission bombs. This led to a marked shift in military weapons development, not only in the U.S. but in the Soviet Union, its Cold War enemy. The first weaponized fusion device was detonated by the U.S. on Eniwetok Island, also in the Pacific, in 1957. That one was 750 times more powerful than the bomb that destroyed Hiroshima and killed more than 140,000 of the city's residents. Much bigger ones have been constructed since.