1946 nuclear weapon tests at Bikini Atoll
Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity on July 16, 1945, and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9, 1945. The purpose of the tests was to investigate the effect of nuclear weapons on warships.
The Crossroads tests were the first of many nuclear tests held in the Marshall Islands and the first to be publicly announced beforehand and observed by an invited audience, including a large press corps. They were conducted by Joint Army/Navy Task Force One, headed by Vice Admiral William H. P. Blandy rather than by the Manhattan Project, which had developed nuclear weapons during World War II. A fleet of 95 target ships was assembled in Bikini Lagoon and hit with two detonations of Fat Man plutonium implosion-type nuclear weapons of the kind dropped on Nagasaki in 1945, each with a yield of .
The first test was "Able". The bomb was named "Gilda" after Rita Hayworth's character in the 1946 film "Gilda" and was dropped from the B-29 Superfortress "Dave's Dream" of the 509th Bombardment Group on July 1, 1946. It detonated above the target fleet and caused less than the expected amount of ship damage because it missed its aim point by .
The second test was "Baker". The bomb was known as "Helen of Bikini" and was detonated underwater on July 25, 1946. Radioactive sea spray caused extensive contamination. A third deep-water test named "Charlie" was planned for 1947 but was canceled primarily because of the United States Navy's inability to decontaminate the target ships after the "Baker" test. Ultimately, only nine target ships were able to be scrapped rather than scuttled. "Charlie" was rescheduled as Operation Wigwam, a deep-water shot conducted in 1955 off the coast of Mexico (Baja California).
Bikini's native residents were evacuated from the island on board the "LST-861", with most moving to the Rongerik Atoll. In the 1950s, a series of large thermonuclear tests rendered Bikini unfit for subsistence farming and fishing because of radioactive contamination. Bikini remains uninhabited as of 2017[ [update]], though it is occasionally visited by sport divers. 
Planners attempted to protect participants in the Operation Crossroads tests against radiation sickness, but one study showed that the life expectancy of participants was reduced by an average of three months. The "Baker" test's radioactive contamination of all the target ships was the first case of immediate, concentrated radioactive fallout from a nuclear explosion. Chemist Glenn T. Seaborg, the longest-serving chairman of the Atomic Energy Commission, called "Baker" "the world's first nuclear disaster."
Background.
The first proposal to test nuclear weapons against naval warships was made on August 16, 1945, by Lewis Strauss, future chairman of the Atomic Energy Commission. In an internal memo to Secretary of the Navy James Forrestal, Strauss argued, "If such a test is not made, there will be loose talk to the effect that the fleet is obsolete in the face of this new weapon and this will militate against appropriations to preserve a postwar Navy of the size now planned." With very few bombs available, he suggested a large number of targets widely dispersed over a large area. A quarter century earlier, in 1921, the Navy had suffered a public relations disaster when General Billy Mitchell's bombers sank every target ship the Navy provided for the ship-versus-bomb tests. The Strauss test would be designed to demonstrate ship survivability.
In August 1945, Senator Brien McMahon, who within a year would write the Atomic Energy Act and organize and chair the Congressional Joint Committee on Atomic Energy, made the first public proposal for such a test, but one designed to demonstrate the vulnerability rather than survivability of ships. He proposed dropping an atomic bomb on captured Japanese ships and suggested, "The resulting explosion should prove to us just how effective the atomic bomb is when used against the giant naval ships." On September 19, the Chief of the United States Army Air Forces (USAAF), General of the Army Henry H. Arnold, asked the Navy to set aside 10 of the 38 captured Japanese ships for use in the test proposed by McMahon.
Meanwhile, the Navy proceeded with its own plan, which was revealed at a press conference on October 27 by the Commander in Chief, United States Fleet, Fleet Admiral Ernest King. It involved between 80 and 100 target ships, most of them surplus U.S. ships. As the Army and the Navy maneuvered for control of the tests, Assistant Secretary of War Howard C. Peterson observed, "To the public, the test looms as one in which the future of the Navy is at stake ... if the Navy withstands [the tests] better than the public imagines it will, in the public mind the Navy will have 'won.'"
The Army's candidate to direct the tests, Major General Leslie Groves, head of the Manhattan Project which built the bombs, did not get the job. The Joint Chiefs of Staff decided that because the Navy was contributing the most men and materiel, the test should be headed by a naval officer. Commodore William S. "Deak" Parsons was a naval officer who had worked on the Manhattan Project and participated in the bombing of Hiroshima. He had been promoted to assistant to the Deputy Chief of Naval Operations for Special Weapons, Vice Admiral William H. P. Blandy, whom Parsons proposed for the role. This recommendation was accepted, and on January 11, 1946, President Harry S. Truman appointed Blandy as head of Army/Navy Joint Task Force One (JTF-1), which was created to conduct the tests. Parsons became Deputy Task Force Commander for Technical Direction. USAAF Major General William E. Kepner was Deputy Task Force Commander for Aviation. Blandy codenamed the tests Operation Crossroads.
Under pressure from the Army, Blandy agreed to crowd more ships into the immediate target area than the Navy wanted, but he refused USAAF Major General Curtis LeMay's demand that "every ship must have a full loading of oil, ammunition, and fuel." Blandy's argument was that fires and internal explosions might sink ships that would otherwise remain afloat and be available for damage evaluation. When Blandy proposed an all-Navy board to evaluate the results, Senator McMahon complained to Truman that the Navy should not be "solely responsible for conducting operations which might well indeed determine its very existence." Truman acknowledged that "reports were getting around that these tests were not going to be entirely on the level." He imposed a civilian review panel on Operation Crossroads to "convince the public it was objective."
Opposition.
Pressure to cancel Operation Crossroads altogether came from scientists and diplomats. Manhattan Project scientists argued that further testing was unnecessary and environmentally dangerous. A Los Alamos study warned "the water near a recent surface explosion will be a witch's brew" of radioactivity. When the scientists pointed out that the tests might demonstrate ship survivability while ignoring the effect of radiation on sailors, Blandy responded by adding test animals to some of the ships, thereby generating protests from animal rights advocates. J. Robert Oppenheimer declined an invitation to attend the test and wrote President Truman about his objections to it, arguing that any data obtained from the test could be obtained more accurately and cheaply in a laboratory.
Secretary of State James F. Byrnes, who a year earlier had told physicist Leo Szilard that a public demonstration of the bomb might make the Soviet Union "more manageable" in Europe, now argued the opposite: that further display of U.S. nuclear power could harden the Soviet Union's position against acceptance of the Acheson–Lilienthal Plan, which discussed possible methods for the international control of nuclear weapons and the avoidance of future nuclear warfare. At a March 22 cabinet meeting he said, "from the standpoint of international relations it would be very helpful if the test could be postponed or never held at all." He prevailed on Truman to postpone the first test for six weeks, from May 15 to July 1. For public consumption, the postponement was explained as an opportunity for more Congressional observers to attend during their summer recess.
When Congressmen complained about the destruction of $450 million worth of target ships, Blandy replied that their true cost was their scrap value at $10 per ton, only $3.7 million. Veterans and legislators from New York and Pennsylvania requested to keep their namesake battleships as museum ships, as Texas had done with , but the JTF-1 replied that "it is regretted that such ships as the cannot be spared."
Preparation.
A series of three tests was recommended to study the effects of nuclear weapons on ships, equipment, and materiel. The test site had to be in territory controlled by the United States. The inhabitants would have to be evacuated, so it was best if it was uninhabited, or nearly so, and at least from the nearest city. So that a B-29 Superfortress could drop a bomb, there had to be an airbase within . To contain the target ships, it needed to have a protected anchorage at least wide. Ideally, it would have predictable weather patterns and be free of severe cold and violent storms. Predictable winds would avoid having radioactive material blown back on the task force personnel, and predictable ocean currents would allow material to be kept away from shipping lanes, fishing areas, and inhabited shores. Timing was critical because Navy manpower required to move the ships was being released from active duty as part of the post-World War II demobilization, and civilian scientists knowledgeable about atomic weapons were leaving federal employment for college teaching positions.
On January 24, Blandy named the Bikini Lagoon as the site for the two 1946 detonations, "Able" and "Baker". The deep underwater test, "Charlie", scheduled for early 1947, would take place in the ocean west of Bikini. Of the possible places given serious consideration, including Ecuador's Galápagos Islands, Bikini offered the most remote location with a large protected anchorage, suitable but not ideal weather, and a small, easily moved population. It had come under exclusive United States control on January 15, when Truman declared the United States to be the sole trustee of all the Pacific islands captured from Japan during the war. The Navy had been studying test sites since October 1945 and was ready to announce its choice of Bikini soon after Truman's declaration. On February 6, the survey ship "Sumner" began blasting channels through the Bikini reef into the lagoon. The local residents were not told why.
The 167 Bikini islanders first learned their fate four days later, on Sunday, February 10, when Navy Commodore Ben H. Wyatt, United States military governor of the Marshall Islands, arrived by seaplane from Kwajalein. Referring to Biblical stories which they had learned from Protestant missionaries, he compared them to "the children of Israel whom the Lord saved from their enemy and led into the Promised Land." He also claimed it was "for the good of mankind and to end all world wars." There was no signed agreement, but he reported by cable "their local chieftain, referred to as King Juda, arose and said that the natives of Bikini were very proud to be part of this wonderful undertaking." On March 6, Wyatt attempted to stage a filmed reenactment of the February 10 meeting in which the Bikinians had given away their atoll. Despite repeated promptings and at least seven retakes, Juda confined his on-camera remarks to, "We are willing to go. Everything is in God's hands." The next day, LST-861 moved them and their belongings east to the uninhabited Rongerik Atoll, to begin a permanent exile. Three Bikini families returned in 1974 but were evacuated again in 1978 because of radioactivity in their bodies from four years of eating contaminated food. As of 2022, the atoll remains unpopulated.
Ships.
To make room for the target ships, of dynamite were used to remove coral heads from Bikini Lagoon. On the grounds of the David Taylor Model Basin outside Washington, DC, dress rehearsals for "Baker" were conducted with dynamite and model ships in a pond named "Little Bikini." A fleet of 93 target vessels was assembled in Bikini Lagoon. At the center of the target cluster, the density was 20 ships per square mile (7.7 per km2), three to five times greater than military