Mushroom cloud from the first test of a hydrogen bomb, 1952.

UNITED STATES - DECEMBER 01: The mushroom cloud produced by the first explosion by the Americans of a hydrogen bomb at Eniwetok Atoll in the South Pacific. Known as Operation Ivy, this test represented a major step forwards in terms of the destructive power achievable with atomic weapons. The hydrogen, or fusion, bomb used a fission device similar to those dropped on Hiroshima and Nagasaki at the end of World War II, detonated inside a container containing deuterium. The high temperatures involved set off a fusion reaction in the deterium, releasing vast amounts of energy. The yield of the weapon was 10.4 megatonnes, more than the total of all the high explosive detonated in the entire duration of the Second World War. (Photo by SSPL/Getty Images)