Shot Mike was the first detonation of a true thermonuclear device, fired on 1 November 1952 as part of Operation Ivy at Elugelab Island, Enewetak Atoll in the Pacific. It was the first weapon built on the Teller-Ulam principle of staged radiation implosion — the design that would define all subsequent hydrogen bombs. The device was designed by the Panda Committee under J. Carson Mark at Los Alamos; Edward Teller declined to participate in its development. Codenamed Sausage, it used liquid deuterium as fusion fuel and weighed approximately 74 metric tonnes — too large and too dependent on cryogenic systems to be a deployable weapon. It was a proof of principle, not a bomb. The yield was 10.4 megatons, making it the fourth largest device ever tested by the United States. Elugelab Island was completely obliterated. The resulting crater measured approximately 1,900 metres across and 50 metres deep. Elevated radiation levels blanketed much of Enewetak Atoll in the aftermath.