National Archives

A colorized photo of the Baker detonation from Operation Crossroads. The underwater detonation rained down unanticipated fallout over a large area, covering the entire target fleet.

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In July of 1946, the US military conducted a pair of nuclear weapons tests on the previously inhabited island of Bikini, a coral atoll in the Marshall Islands chain. Advertised as a “defensive” test to see how ships would withstand a nuclear blast, the tests—code-named “Crossroads”—were described by the Manhattan Project team as “the most publicly advertised secret test ever conducted.”

The National Security Archive project at George Washington University has assembled a collection of documents and videos related to the Bikini tests—the second of which would be called “the world’s first nuclear disaster”by Atomic Energy Commission chairman Glenn T. Seaborg. The Baker explosion, detonated underwater, was the first to create significant fallout, as a “base surge” of irradiated water and debris washed over the entire fleet of target ships and Bikini’s lagoon itself.

Bikini was chosen for its deep, large lagoon, and because the island was far off international shipping routes. To prepare the site, the US Navy (which governed the Marshall Islands immediately following World War II) convinced the inhabitants of Bikini to relocate for the tests, which military governor Commodore Ben Wyatt told them was for “the good of all mankind and to end all world wars.”