Nuclear testing at Bikini Atoll

Nuclear testing at Bikini Atoll consisted of the detonation of 24 nuclear weapons by the United States between 1946 and 1958 on Bikini Atoll in the Marshall Islands. Tests occurred at 7 test sites on the reef itself, on the sea, in the air, and underwater.^[1] The test weapons produced a combined yield of about 75 Mt of TNT in explosive power. After the inhabitants agreed to a temporary evacuation, two nuclear weapons were detonated in 1946. About ten years later, additional tests with thermonuclear weapons in the late 1950s were also conducted. The first thermonuclear explosion was much more powerful than expected, and created a number of issues, but did demonstrate the dangers of such devices.

The United States and its allies were engaged in a Cold War nuclear arms race with the Soviet Union to build more advanced bombs from 1947 until 1991.^[2] The first series of tests over Bikini Atoll in July 1946 was codenamed Operation Crossroads. The first bomb, named Able, was dropped from an aircraft and detonated 520 ft (160 m) above the target fleet. The second, Baker, was suspended under a barge. It produced a large Wilson cloud and contaminated all of the target ships. Chemist Glenn T. Seaborg, the longest-serving chairman of the Atomic Energy Commission, called the second test "the world's first nuclear disaster."^[3] A third test, Charlie, was cancelled due to concerns over the lingering radiation from Baker's detonation.

The second series of tests in 1954 was codenamed 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: the 15 Mt of TNT nuclear explosion far exceeded the expected yield of 4–8 Mt of TNT (6 predicted).^[4] This was about 1,000 times more powerful than either of the atomic bombs dropped on Hiroshima and Nagasaki during World War II.^[5] The scientists and military authorities were shocked by the size of the explosion, and many of the instruments that they had put in place to evaluate the effectiveness of the weapon were destroyed.^[2]

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 provides residents with on-going aid. Despite the promises made by authorities, these 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 has paid more than $300 million into various trust funds to compensate the islanders and their descendants.^[6] A 2016 investigation found radiation levels on Bikini Atoll as high as 639 mrem yr⁻¹ (6.39 mSv/a), well above the established safety standard for habitation.^[7][8] However, Stanford University scientists reported "an abundance of marine life apparently thriving in the crater of Bikini Atoll" in 2017.^[9]