Atomic bomb explosion. Mushroom cloud produced by the detonation of XX-28 George, a 225-kiloton nuclear bomb, on 8 May 1951. This was one of a series of four detonations carried out during Operation Greenhouse on Enewetak Atoll in the Pacific Ocean during April and May 1951. XX-28 George was one of the first tests of thermonuclear fusion and was a purely experimental device. It was detonated from a 60-metre-high tower on the island of Eberiru. The yield of the fusion reaction was negligible compared to the fission device, unlike that of Ivy Mike, the first 'true' thermonuclear fusion device tested in 1952.