The United States was engaged in a Cold War nuclear arms race with the Soviet Union to build more advanced bombs from 1947 until 1991 . The first series of tests over Bikini Atoll in July 1946 was code named Operation Crossroads . The first test was dropped from an aircraft and detonated above the target fleet . The second was '' Baker '' and was suspended under a barge . It produced a large Wilson cloud and contaminated all of the target ships . Chemist Glenn T. Seaborg was the longest-serving chairman of the Atomic Energy Commission , and he called the second test " the world 's first nuclear disaster . " The second series of tests in 1954 was code named Operation Castle . The first detonation was Castle Bravo , which tested a new design utilizing a dry fuel thermonuclear bomb . It was detonated at dawn on March 1 , 1954 . Scientists miscalculated and the 15 megaton ( Mt ) nuclear explosion far exceeded the expected yield of 4 to 8 Mt ( 6 Mt predicted ) , and was about 1,000 times more powerful than each of the atomic bombs dropped on Hiroshima and Nagasaki during World War II . The scientists and military authorities were shocked by the size of the explosion , and many instruments were destroyed which they had put in place to evaluate the effectiveness of the weapon . Authorities had promised the Bikini Atoll 's residents that they would be able to return home after the nuclear tests . A majority of the island 's family heads agreed to leave the island , and most of the residents were moved to the Rongerik Atoll and later to Kili Island . Both locations proved unsuitable to sustaining life , and the United States had to provide residents with on-going aid . Despite the promises made by authorities , this and further nuclear tests ( Redwing in 1956 and Hardtack in 1958 ) rendered Bikini unfit for habitation , contaminating the soil and water , making subsistence farming and fishing too dangerous . The United States later paid the islanders and their descendants $ 125 million in compensation for damage caused by the nuclear testing program and their displacement from their home island . A 2016 investigation found radiation levels on Bikini Atoll as high as 639 mrem yr & minus ; 1 , well above the established safety standard for habitation . However , Stanford University scientists reported " an abundance of marine life apparently thriving in the crater of Bikini Atoll " in 2017 . Research is being undertaken on how marine organisms are surviving in a radiation-filled environment , which could lead to improved understanding of cancer and increased longevity
Castle Bravo
Castle Bravo
Nuclear testing at Bikini Atoll