A weapon deriving a large portion of its energy from the nuclear fusion of hydrogen isotopes.

In fusion, lighter elements are joined together to form heavier elements, and the end product weighs less than the components forming it. The difference in mass is converted into energy. Because extremely high temperatures are required to initiate fusion reactions, a hydrogen bomb is also known as a thermonuclear bomb.

The presumable structure of a hydrogen bomb is as follows an Atomic Bomb is surrounded by a layer of lithium deuteride (compound of lithium and deuterium) and then by a tamper, or thick outer layer, frequently of fissionable material, that holds the content together in order to obtain a larger explosion.

The atomic explosion produces neutrons that fission the lithium into helium, tritium, and energy, and also produces the extremely high temperature needed for the subsequent fusion of deuterium with tritium and tritium with tritium.

The first thermonuclear bomb was exploded in 1952 at Enewetak by US the second in 1953 by the U.S.S.R.