Bikini Atoll mushroom cloud

Suspended 90 feet below the sea, anchored beneath an auxiliary craft in the midst of the target ghost fleet, the detonation of Test Baker marked the first-ever underwater nuclear explosion when the 23 kiloton device was detonated on July 25, 1946, at the Bikini Atoll lagoon, Marshall Islands, in the Pacific Ocean.

The device, which displaced 2 million tons of water, was the fifth of over 2,000 nuclear explosions conducted to date by the U.S. military. Only a few of the tests were underwater explosions, carried out primarily to research the impact to ships and submarines.

Test Baker, and Test Able on July 1, 1946, were part of "Operation Crossroads," a series of nuclear tests conducted during 1946. The massive project sought to answer questions about the effects of nuclear weapons on a fleet of ships and living animals. The operation involved 42,000 personnel, 242 ships, 156 airplanes, and the relocation of all 162 residents from the Bikini Atoll.

The Marshall Islands became quite familiar with the nuclear studies of the U.S. military. The Bikini Atoll became the site of another nuclear first when a B-52 dropped the first airborne hydrogen bomb on May 21, 1956.

The mushroom cloud and water column seen here resulted from the underwater Test Baker nuclear explosion of July 25, 1946, as seen from an observation tower on Bikini Island, 3.5 miles away from ground zero.
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Photo by: U.S. Navy / Caption by:

Detonation of Test Baker

A fleet of more than 90 vessels was assembled in Bikini Lagoon as a target with which to study the effects of the blast.

This target fleet consisted of older U.S. capital ships, three captured German and Japanese ships, surplus U.S. cruisers, destroyers, and submarines, and a large number of auxiliary and amphibious vessels.
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Photo by: U.S. Navy / Caption by:

Mushroom cloud with ships below

The mushroom cloud from Test Baker with ships visible below during Operation Crossroads nuclear weapons test on Bikini Atoll.

Military equipment was also arrayed on some of the ships, and amphibious craft were berthed on Bikini Island. Following the test, the target fleet remained too radiologically contaminated for several weeks to do anything more than brief on-board research activities.

The inability to complete inspections on much of the target fleet threatened the success of the operation after Test Baker.
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Photo by: U.S. Navy / Caption by:

Able and Baker, the fourth and fifth tests

The blast from the 23 kiloton underwater nuclear weapons effects test, known as Operation Crossroads.

The bombs that ended World War II on August 6 and August 9, 1945, at Hiroshima and Nagasaki were the second and third nuclear detonations on Earth. The first bomb was detonated at Alamagordo, N.M., on July 16, 1945.

Operation Crossroads tests Able and Baker were the fourth and fifth tests, seeking a greater understanding of these powerful tools of war.
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Photo by: U.S. Navy / Caption by:

Water falls back from the stem

As water falls back from the stem, it forms a dense highly radioactive cloud called the "base surge." The stern of one of the target fleet ships, the USS Saratoga, can be seen rising 43 feet on the crest of the first wave, which was measured to be 94 feet high and 1,000 feet from surface zero. Waves six feet high were seen 22,000 feet from the explosion.
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Photo by: U.S. Navy / Caption by:

Mushroom cloud with ships below

Mushroom cloud with ships below during Operation Crossroads nuclear weapons test on Bikini Atoll. About 750 cameras and 75,000 radiation recorders were set up to watch the destructive scientific event and better understand the forces involved, pressure, shockwave velocity, accelerations, and intensity of gamma radiation.
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Photo by: U.S. Navy / Caption by:

Contaminated ships

Following Test Baker at Bikini Atoll, a program of target vessel decontamination was begun August 1, 1946. Here, a Navy fireboat washes down battleship New York to reduce radioactive contamination after the blast passed over it.

Operation Crossroads consisted of two 23 kiloton nuclear detonations. Test Able detonated at an altitude of 520 feet on July 1, 1946, and Test Baker was detonated 90 feet underwater on July 25, 1946.

A third planned detonation, Test Charlie, was canceled after the United States Navy was unable to decontaminate ships used in the Test Baker experiments.
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Photo by: U.S. Navy / Caption by:

Decontamination efforts aboard Prinz Eugen

In an attempt to remove radioactive contamination, sailors scrub down the German cruiser Prinz Eugen during decontamination efforts aboard the German cruiser Prinz Eugen. The Navy was unable to decontaminate the target ships used in Test Baker, which led to the cancellation of a third shot, Test Charlie, which had been planned as part of Operation Crossroads.
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Photo by: U.S. Navy / Caption by:

Target ships at Pearl Harbor

Prospective target ships to be used as part of the Operation Crossroads tests including the Gilliam-class attack transports USS Crittenden, Catron, Bracken, Burleson, Gilliam, Fallon, and USS Fillmore are seen here at Pearl Harbor prior to the nuclear testing.
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Photo by: U.S. Navy / Caption by:

Drones, 1946

The Grumman F6F-3 Hellcat used to monitor radio activity at Bikini after the Test Baker blast is located at the Smithsonian's National Air and Space Museum's Udvar-Hazy Center.

The plane was launched unmanned soon after the bomb was detonated on July 25, 1946. Instruments on board and photographic plates taped to the control stick obtained data on radioactivity. Unmanned drones -- which at the time were a huge feat for the military -- played numerous roles in these early nuclear tests.

It was the first operation in which takeoff, flight, and landing were accomplished with no one aboard. Drones are common in today's advanced military, but in 1946, the feat was an impressive one: many experts had thought it could never be accomplished with planes of this size.
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Photo by: Smithsonian Institution / Caption by:

Mushroom cloud cake

Admiral William H.P. Blandy, left, his wife, and Rear Admiral F.J. Lowry, right, cut into a mushroom cloud cake on November 7, 1946, to celebrate the end of Operation Crossroads.
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Photo by: U.S. Navy / Caption by:

Radioactivity has entered the food chain

Following the two tests conducted during Operation Crossroads, scientific surveys in the Marshall Islands sought to determine the effects of the nuclear blasts.

U.S. National Museum curator Leonard Schultz, kneeling at right, reviews specimens collected as part of the Bikini Resurvey in 1947. Also pictured, from left, are Vernon Brock, the director of fish and game division for the territory of Hawaii, A.C. Cole, professor of zoology and entomology at the University of Tennessee, and R.W. Hiatt of the U.S. Fish and Wildlife Service.

Scientists concluded: "Clearly radioactivity had entered the food chain. Plankton glowed on photographic plates, as did the intestinal tracts of the fish that fed on them. Only long term studies would show if the atoll would ever return to the ecological balance it enjoyed before Able Day."

Half a century later in 1997, the International Atomic Energy Agency reported that the Bikini Atoll was still uninhabitable.
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Photo by: National Museum of Natural History, Smithsonian Institution / Caption by:
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