Nuclear security

The H-bomb: What is it? Who has it? Why it matters

A hydrogen bomb is a complex bit of machinery. It's basically two bombs in one.

While it gets its bang from fusion, it takes a lot of heat to get the process started -- to get the atoms to smash together and start a nuclear chain reaction. That's why they're called thermonuclear weapons.

What better to do that with than another much smaller nuclear weapon. An atomic bomb works as the trigger to set off the hydrogen bomb. The two explosions are almost simultaneous.

The nuclear arsenals of the United States, Russia, United Kingdom, France and China are made up of these types of weapons.

India and Pakistan are believed to have atomic bombs.