Operation Ivy was the first-ever series of
hydrogen bomb tests, carried out by Joint
Task Force 132 at
Enewetak Atoll in the
Pacific Proving Grounds. The tests were coordinated by the
Atomic Energy Commission and the
Joint Chiefs of Staff. The first
bomb dropped in this operation was "Mike", a 10.4 megaton blast roughly 750 times as
powerful as the
atomic bomb dropped on
Hiroshima. Mike vaporized the entire test island.
The second Operation Ivy test was the "King" shot, a pure fission device using Oralloy (pure U235) air-dropped on November 19, 1952. King was a 500 kiloton shot, which left a one mile wide crater and blanketed dozens of neighboring islands with radioactive fallout, thanks to the winds (not that dropping an immense nuclear device had anything to do with it...).
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Thanks to Grzcyrgba for the correction on the Ivy King test.