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1955 Sci. Amer. Aug. 46/3 Speculation about the ‘fission-fusion-fission’ bomb..was indirectly confirmed last month by Atomic Energy Commissioner Willard F. Libby. This weapon is said to consist of a fission bomb which triggers a thermonuclear reaction which in turn causes ordinary uranium (238) to fission. In a speech at the University of Chicago, Libby mentioned ‘a nuclear explosion releasing 10 megatons of fission energy’.

1966 Observer 15 May 2/5 ‘Fission-fusion-fission’ means a three-stage bomb with a uranium or fission trigger, a hydrogen or fusion intermediate stage..and an outer case of ‘natural’ uranium 238.