&gt; A proper hydrogen bomb would be purely fusion.<p>But a fission device is used to get the fusion reaction going in all practical designs, I think.<p>The fine article describes the design of the US&#x27;s actual hydrogen bombs as follows - I don&#x27;t know if you&#x27;d count them as &#x27;proper&#x27;:<p>&gt; So there are really three stages of nuclear reaction in such a bomb: the primary (fission), the secondary’s internal fuel (fusion), and the secondary’s casing (more fission).