A doomsday device is a hypothetical construction – usually a weapon or weapons system – which could destroy all life on a planet, particularly Earth, or destroy the planet itself, bringing "doomsday",
Many hypothetical doomsday devices are based on salted hydrogen bombs creating large amounts of nuclear fallout. Above, the Castle Romeo nuclear test (yield 11 megatons) at Bikini Atoll of the Marshall Islands, conducted on a barge moored in the middle of the crater created from the Castle Bravo test and the first nuclear test conducted on a vessel (March 26, 1954).