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Operation Crossroads 1946 Nuclear Tests

Operation Crossroads was a series of nuclear weapon tests conducted by the United States in the summer of 1946. The series consisted of two detonations, each with a yield of 23 kilotons: Able detonated at an altitude of 520 feet (158 m) on 1 July 1946; Baker detonated 90 feet (27 m) underwater on 25 July 1946. A third planned burst, Charlie, was canceled. The Crossroads tests were the fourth and fifth nuclear explosions done by the USA (following the Trinity test and the bombings of Hiroshima and Nagasaki). They were the first nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand.

A series of three tests was recommended to study the effects of nuclear weapons on ships, equipment, and material. Test site requirements were specified:

* A protected anchorage at least six miles wide
* A site which was uninhabited, or nearly so
* A location at least 300 miles from the nearest city
* Weather patterns without severe cold and violent storms
* Predictable winds directionally uniform from sea level to 60000 feet
* Predictable water currents away from shipping lanes, fishing areas, and inhabited shores
* Controlled by the United States

Timing became critical because Navy manpower required to move the ships was being released from active duty, and civilian scientists knowledgeable about atomic weapons were leaving federal employment for college teaching positions requiring their attendance when the fall semester started.

A fleet of more than 90 vessels was assembled in Bikini Lagoon as a target. This target fleet consisted of older U.S. battleships Arkansas, New York, Nevada, and Pennsylvania, aircraft carriers Saratoga and Independence, heavy cruisers Pensacola and Salt Lake City, destroyers, submarines, numerous auxiliary and amphibious vessels, and three surrendered German and Japanese ships. Military equipment was arrayed on some of the ships as well as amphibious craft that were berthed on Bikini Island. Technical experiments were also conducted to study nuclear weapon explosion phenomena. Some experiments included the use of live animals.[2] Bikini target ship USS Burleson (APA-67) brought 200 pigs, 60 guinea pigs, 204 goats, 5000 rats, 200 mice, and grains containing insects to be studied for genetic effects by the National Cancer Institute.

The support fleet of more than 150 ships provided quarters, experimental stations, and workshops for most of the 42,000 men (more than 37,000 of whom were Navy personnel) of Joint Task Force 1 (JTF 1), the organization that conducted the tests. Additional personnel were located on nearby atolls such as Eniwetok and Kwajalein. Navy personnel were allowed to extend their obligated service for one year if they wanted to to participate in the tests and see an atomic bomb explode. Many of the civilian scientists also volunteered for project participation to see an atomic bomb explode. The islands of the Bikini Atoll were used primarily as recreation and instrumentation sites.

Before the first test, all personnel were evacuated from the target fleet and Bikini Atoll. These men were placed on units of the support fleet, which sortied from Bikini Lagoon and took safe positions at least 10 nautical miles (18.5 km) east of the atoll. Test personnel were issued special dark glasses to protect their eyes, but a decision was made shortly before test Able that the glasses might not be protective; and personnel were instructed to turn away from the blast, shut their eyes, and cradle their arm across their face for additional protection. A few observers who disregarded the recommended precautions advised the others when the bomb detonated. Most shipboard observers reported feeling a slight concussion and hearing a disappointing little "poom".

Ships sunk during test Able
A painting of USS Gilliam and Carlisle under the blast.

* Sakawa, an Imperial Japanese Navy cruiser
* USS Anderson (DD-411)
* USS Lamson (DD-367)
* USS Carlisle (APA-69)
* USS Gilliam (APA-57)

Ships sunk during test Baker, 25 July 1946

* Nagato, an Imperial Japanese Navy battleship
* USS Arkansas (BB-33)
* USS Saratoga (CV-3)
* USS Apogon (SS-308)
* USS Pilotfish (SS-386)
* Concrete Auxiliary Repair Dock (ARDC-13)
* Landing Ship USS LSM-60 (Surface Zero Ship)
* District Craft YO-160

The ex-German heavy cruiser Prinz Eugen survived both the Able and Baker tests but was too radioactive to have leaks repaired. In September 1946 she was towed to Kwajalein Atoll where she capsized on 22 December 1946.

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Added: Nov-13-2008 
By: Thyrsoid
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Tags: Operation Crossroads, 1946, Nuclear, Tests, United States
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