Since the 1954
Castle Bravo thermonuclear weapon test demonstrated the feasibility of making arbitrarily large nuclear devices which could cover vast areas with radioactive fallout by rendering anything around them intensely radioactive, nuclear weapons theorists such as
Leo Szilard conceived of a doomsday machine, a massive thermonuclear device surrounded by hundreds of tons of cobalt which, when detonated, would create massive amounts of
Cobalt-60, rendering most of the Earth too radioactive to support life.
RAND strategist
Herman Kahn postulated that Soviet or US nuclear decision makers might choose to build a doomsday machine that would consist of a computer linked to a stockpile of hydrogen bombs, programmed to detonate them all and bathe the planet in
nuclear fallout at the signal of an impending nuclear attack from another nation. The doomsday device's theoretical ability to deter a nuclear attack is that it would go off automatically without human aid and despite human intervention. Kahn conceded that some planners might see "doomsday machines" as providing a highly credible threat that would dissuade attackers and avoid the dangerous game of
brinkmanship caused by the
massive retaliation concept which governed US-Soviet nuclear relations in the mid-1950s. However, in his discussion of doomsday machines, Kahn raises the problem of a nuclear-armed
Nth country triggering a doomsday machine, and states that he didn't advocate that the US acquire a doomsday machine. The
Dead Hand (or "Perimeter") system built by the
Soviet Union during the
Cold War has been called a "doomsday machine" due to its
fail-deadly design and nuclear capabilities. == In fiction ==