The nuclear testing at Bikini Atoll program was a series of 23 nuclear devices detonated by the United States between 1946 to 1958. Test weapons were detonated on the reef itself, on the sea, in the air and underwater. The actual island, Bikini Atoll, is one island of 23 islands that comprises the Marshall Islands in the Pacific Ocean. Nuclear testing began in July of 1946 with Operation Crossroads. The nukes rendered the island and surrounding area uninhabitable due to radioactivity, stemming mostly from caesium-137.