These nuclear bomb detonations, (known as the Able and Baker Tests respectively), took place in July 1946 as part of Operation Crossroads on the island of Bikini Atoll in the Pacific. A fleet of decommissioned US and seized Japanese vessels were deployed in the area with the intention of simulating and documenting the effects of nuclear weapons in naval warfare. They were the precursors to a series of large thermonuclear tests that over the next decade or so would render Bikini unfit for human habitation, a situation that is only recently beginning to reverse itself.



The first experiment of Operation Crossroads, the Able Test, occurred on July 1 when a bomb was dropped from the B-29 Super-Fortress Dave's Dream of the 509th Bombardment Group; the same plane that was used as the photographic equipment aircraft on the Nagasaki mission in 1945. The 23-kiloton air-deployed nuclear weapon was detonated 520 feet (158 m) above the target fleet though the bomb missed its aim point by 710 yards (649 m) which led to less than spectacular results.



The bomb used for the Baker Test on July 25 was the same design as the one used on Nagasaki in the previous year and in this test was detonated ninety feet underwater amongst the target fleet. More successful than Able, it is most remembered for producing a series of unique photographs because the blinding flash of the explosion that normally obscures the target area was mostly unseen as it was underwater. The large Wilson cloud and the vertical water column are characteristic Baker shot features and the clear images of the surrounding ships give a good sense of the scale of the mushroom cloud.

Sources:

rarehistoricalphotos.com
wikipedia.org