Thermonuclear bomb explosion. (Source: Wikipedia.org)

A destructive weapon based on an uncontrolled fusion reaction. The bomb typically consists of two parts (the so-called Teller-Ulam design). The first (primary) contains the fission bomb, which, by its explosion, generates enough energy to compress the second part (secondary), in which the fusion is ignited.

The hydrogen bomb has never been used. The largest hydrogen bomb ever made was the Russian 50 Mt Tsar bomb, a single example of which was tested in 1961.