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.
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.”
A task force of over 42,000 people, including 38,000 from the Navy as well as over 3,000 from the Army and scientists and technicians from 15 universities and various defense contractors and other organizations, was organized for Operation Crossroads. A total of 94 vessels, ranging from aircraft carriers to landing craft, was moored in the lagoon of Bikini as a target fleet, carrying fuel and ammunition as well as a collection of tanks, trucks and other military equipment. Twenty-two of the ships were “crewed” by 109 mice, 146 pigs, 176 goats, 57 guinea pigs and 3,030 white rats (a fact that caused the tests to be widely protested by animal welfare organizations).
The fleet of target ships included aircraft carriers, battleships, cruisers, destroyers, submarines, and landing craft, among other ships. Some of the vessels had been declared excess inventory after the Navy had scaled down its forces, and others had been damaged during World War II. Three German and Japanese warships captured during the war were among the ships to be targeted.
The Able and Baker bombs were the same type of warheads used in the bombing of Nagasaki. But the results of the two tests were vastly different. Able was dropped from a B-29 Superfortress bomber, detonating in the air nearly a half mile from the intended target–the battleship USS Nevada. It sank five ships, and damaged another 40, many of them beyond potential repair. And while the Nevada survived the Able blast, neutron and gamma radiation penetrated the whole ship, killing the goats aboard standing in for its crew. Even in the deepest parts of the ship, radiation was measured at above a lethal dose. The Bulletin of the Atomic Scientist noted in its report on the test, that it showed “a large ship, about a mile away from the explosion, would escape sinking, but the crew would be killed by the deadly burst of radiations from the bomb, and only a ghost ship would remain, floating unattended in the vast waters of the ocean.”
But Able caused no significant contamination to the ships. While there was some metal aboard the ships rendered radioactive by the neutron bombardment, the ships were safely boarded within days of the Able blast, and there was little fallout.
Baker was detonated underwater, suspended 90 feet below a landing craft (of which no identifiable part was ever found after the test). Nine ships were sunk by the detonation, including the battleship USS Arkansas. Many others were damaged severely by the shockwave and the tsunami that followed the collapse of the gas bubble created by the detonation. But the entire target fleet was engulfed by a “base surge”–a cascade of radioactive flotsam that spread out from the detonation, engulfing most of the test area and contaminating everything in its path with fallout. The degree of fallout was far beyond anything the military had prepared for.
The Navy initially attempted to decontaminate many of the surviving ships from the Baker test. But nothing short of taking them down to bare metal worked, and the Navy crews were unprepared to deal with decontamination on such a large scale. Many were exposed to high levels of radiation. The radiological safety officer for Operation Crossroads, Army doctor Colonel Stafford Warren, lobbied hard to abandon the effort, and finally convinced the head of the task force, Deputy Chief of Naval Operations Admiral William H. P. Blandy, by showing him an x-ray of a fish from the lagoon–an x-ray taken using only the radiation coming from plutonium in the fish itself.