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...).
Thanks to Grzcyrgba for the correction on the Ivy King test.