Nuclear fusion is a reaction that releases atomic energy by the union of light nuclei at high temperatures to form heavier atoms. Hydrogen bombs, which use nuclear fusion, have higher destructive power and greater efficiencies than atomic bombs.

Due to the high temperatures required to initiate a nuclear fusion reaction, the process is often referred to as a thermonuclear explosion. This is typically done with the isotopes of hydrogen (deuterium and tritium) which fuse together to form Helium atoms. This led to the term "hydrogen bomb" to describe the deuterium-tritium fusion bomb.

The first hydrogen bomb was exploded on November 1, 1952 at the small island Eniwetok in the Marshall Islands. Its destructive power was several megatons of TNT. The blast, timed at 19:15 GMT, produced a light brighter than a 1,000 suns and a heat wave felt 50 kilometres away. The Soviet Union detonated a hydrogen bomb in the megaton range in August of 1953. The US exploded a 15 megaton hydrogen bomb on March 1, 1954. It had a fireball of 4.8 km in diameter and created a huge mushroom-shaped cloud.

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US drops the world’s first H-Bomb

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