Manhattan Project: Operation Crossroads, Bikini Atoll, July 1946

OPERATION CROSSROADS
(Bikini Atoll, July 1946)
Events > Postscript -- The Nuclear Age, 1945-present

Even after the Trinity test and the bombings of Hiroshima and Nagasaki, military officials still knew far less than they would have liked about the effects, especially on naval targets, of nuclear weapons. Accordingly, the Joint Chiefs of Staff requested and received presidential approval to conduct a series of tests during summer 1946. Vice Admiral W. H. P. Blandy, head of the test series task force, proposed calling the series Operation "Crossroads." "It was apparent," he noted, "that warfare, perhaps civilization itself, had been brought to a turning point by this revolutionary weapon."

Experience with the radiological hazards of Trinity and the two bombs dropped on Japan strongly influenced the decision to locate Crossroads at Bikini Atoll in the Marshall Islands of the central Pacific, far from major population centers. Bikini was a typical coral atoll. With a reef surrounding a lagoon of well over 200 square miles, Bikini offered ample protected anchorage for both a target fleet and support ships. As a test site, the atoll held two drawbacks: the distance from the continental United States imposed extraordinary logistical demands, and the humid climate created numerous problems for sophisticated electronic and photographic equipment. The military removed the native population of 162 to another atoll and brought in a large, invited audience of journalists, scientists, military officers, congressmen, and foreign observers.

The first test, Shot "Able" (left), a plutonium bomb dropped from a B 29 on July 1, performed as well as the plutonium devices used at Trinity and Nagasaki. Able nonetheless failed to fulfill its pre-test publicity buildup. Partly this was because expectations had been too extravagant and observers were so far from the test area that they could not see the target array. Partly it was because the drop had missed the anticipated ground zero by some distance and the blast sank only three ships. In any event, the general conclusion reached by the media at Bikini was that the "atomic bomb was, after all, just another weapon." (Click here for a video clip of the Able test.)

The second test, Shot "Baker," proved much more impressive. Detonated ninety feet underwater on the morning of July 25, Baker produced a spectacular display as it wreaked havoc on a seventy four vessel fleet of empty ships and spewed thousands of tons of water into the air. As with Able, the test yielded explosions equivalent to 21,000 tons of TNT. Baker, as one historian notes, "helped restore respect for the power of the bomb." (Click here for a video clip of the Baker test.)

Baker also created a major radiation problem. The test produced a radioactive mist that deposited active products on the target fleet in amounts far greater than had been predicted. As the Joint Chiefs of Staff evaluation board later noted, the contaminated ships "became radioactive stoves, and would have burned all living things aboard them with invisible and painless but deadly radiation." Decontamination presented a significant radiation hazard, and, as a result, over a period of several weeks personnel exposure levels began to climb. A worried Stafford Warren (right), who headed the testing task force's radiological safety section, concluded that the task force faced "great risks of harm to personnel engaged in decontamination and survey work unless such work ceases within the very near future." With exposure data in hand, Warren prevailed and decontamination operations ceased. A planned third shot, to be detonated on the bottom of the lagoon, was canceled. Able and Baker were the final weapon tests conducted by the Manhattan Project and the last American tests until the Atomic Energy Commission's Sandstone series began in spring 1948.

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Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: Terrence R. Fehner and F. G. Gosling, Origins of the Nevada Test Site (DOE/MA-0518; Washington: History Division, Department of Energy, December 2000), 32-34. See also Barton C. Hacker, The Dragon's Tail: Radiation Safety in the Manhattan Project, 1942-1946 (Berkeley, CA: University of California Press, 1987), 116-153; and the History Office publications: Richard G. Hewlett and Oscar E. Anderson, Jr., The New World, 1939-1946: Volume I, A History of the United States Atomic Energy Commission (Washington: U.S. Atomic Energy Commission, 1972), 580-581, and F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 55. The photograph of the evacuation of Bikini islanders is reproduced from Fehner and Gosling, Origins of the Nevada Test Site, 37. The two black and white photographs of the Baker test are courtesy the "Atomic Century" web site (now defunct). The photograph of Able, the color photograph of Baker, and the two video clips are courtesy the Federation of American Scientists. The photograph of Stafford Warren is reprinted in Vincent C. Jones, Manhattan: The Army and the Atomic Bomb, United States Army in World War II (Washington: Center of Military History, United States Army, 1988), 414.

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