60th Anniversary of Castle BRAVO Nuclear Test, the Worst Nuclear Test in U.S. History

28 February 2014 — National Security Archive

Blast Had Far Greater Explosive Yield than Expected, Equivalent to 1,000 Hiroshimas

Fallout from the Test Contaminated the Marshall Islands and Japanese Fishermen on the Fortunate Dragon (Fukuryu Maru)

Consequences of BRAVO Created Outrage around the World and Pressure to Ban Nuclear Weapons Tests

National Security Archive Electronic Briefing Book No. 459

Posted – February 28, 2014

For more information contact:
William Burr – 202/994-7000 or nsarchiv@gwu.edu


Washington, DC, February 28, 2014 — Sixty years ago, on 1 March 1954 (28 February on this side of the International Dateline), on Bikini Atoll in the Marshall Islands, the U.S. government staged the largest nuclear test in American history. The BRAVO shot in the Castle thermonuclear test series had an explosive yield of 15 megatons, 1000 times that of the weapon that destroyed Hiroshima and nearly three times the 6 megatons that its planners expected. To recall this shocking event the National Security Archive posts today a selection of documents about the BRAVO shot and its consequences, mainly from State Department records at the National Archives.

Castle BRAVO spewed radioactive fallout around the world and gravely sickened nearby inhabitants of the Marshall Islands, then under a U.S. trusteeship, and 236 were evacuated as well as 28 American military personnel on a nearby island. Twenty-three Japanese fishermen were also contaminated, which made the test known to the world and roiled U.S-Japanese relations. While the U.S. government claimed at the time that a shift in the wind spread the fallout far from the test site, a recent U.S. government report demonstrates that it was the volcanic nature of the explosion that dumped the fallout nearby. The adverse health effects for inhabitants of Rangelop Atoll, 110 miles away from the test site, were severe and some islands remained uninhabitable for years. This radiological calamity had a significant impact on world opinion and helped spark the movement for a nuclear test moratorium which ultimately led to the 1963 Limited Test Ban Treaty.

Included in this posting is a U.S. Air Force documentary film on the Joint Task Force 7 commander’s report on the Castle Series. It includes footage of the BRAVO shot as well as coverage of the evacuation of U.S. personnel and Marshall Islanders in the wake of the test. The documentary is sanitized at points apparently to protect nuclear weapons design information. A Freedom of Information request by the Archive for a fresh review and a subsequent appeal failed to dislodge more details.

Documents in this posting include:

* Japanese government accounts of the Fukuryu Maru incident
* The May 1954 petition by Marshall Islanders for an end to nuclear tests in the area
* U.S. Embassy Tokyo telegrams on BRAVO’s adverse impact for U.S.-Japanese relations
* Internal U.S. government consideration of compensation to the Japanese government and the Marshall Islands for losses incurred by nuclear testing
* Decisions to delay the return of the inhabitants to Rongelap Atoll because of unsafe conditions
* A comprehensive Defense Threat Reduction Agency report from 2013 on Castle BRAVO exposing “legends and lore” about the test

Why and how exactly U.S. scientists miscalculated the yield remains classified but what made the 15-megaton Bravo shot the worst nuclear test in U.S. history is no secret. The device detonated on an islet in a coral reef, producing massive levels of fallout that quickly reached the stratosphere before falling to earth. It is worth comparing BRAVO to the most powerful nuclear test ever, the Soviet Union’s 50-megaton “Tsar Bomba” of 30 October 1961. That test’s radiological consequences were far less severe because the “Tsar Bomba’s” fireball never touched the earth’s surface producing significantly less fallout than BRAVO. Historian of science Alex Wellerstein has written that Castle BRAVO is a “cautionary tale about hubris and incompetence in the nuclear age — scientists setting off a weapon whose size they did not know, whose effects they did not correctly forecast, whose legacy will not soon be outlived.”

While the “Tsar Bomba” was almost immediately known to the world, the architects of the Castle test series worked in secrecy; the Eisenhower administration wanted to keep words like “hydrogen” and “thermonuclear” out of public discourse and only the fact that tests would be held in the Pacific in 1954 went to the public. After the BRAVO shot occurred, the AEC and the Defense Department sought to control what could be known about the event. But the cat was out of the bag when the Fukuryu Maru crew returned to port which gave Washington a serious damage control problem as information about the 1 March test began to reach the public. At the end of the month AEC chairman Lewis Strauss gave a generally misleading press conference about BRAVO but he managed to alarm the public when he acknowledged that hydrogen bombs could be “made large enough to take out a city … any city.”

Until recently, an extensive collection of documents on nuclear testing in the Marshall Islands was readily available on a Departmen
t of Energy Web site, The Marshall Islands Document Collection. It no longer has an on-line presence. In the fall of 2013, at the time of the U.S. government shut-down, this important collection disappeared from the Web. It is unclear whether the Department intends to restore it as a distinct Web page. Many documents on the Marshall Islands can be found on the Energy Department’s OpenNet but whether they are essentially the same items is also unclear at present. Moreover other documents on nuclear testing in the Marshall Islands that the Energy Department declassified in the 1990s and were once available at the National Archives or on-line were reclassified early in the last decade after the Kyl-Lott amendment went into effect in 1999.


Unique non-U.S. government documents about the consequences of nuclear testing in the Marshall Islands are also at risk. The case files of the Nuclear Claims Tribunal for the Marshall Islands, which went out of existence in 2010, are an irreplaceable record of the impact of nuclear testing on a vulnerable population. The collection of paper records resides in a building in Majuro, the Marshall Island’s capital city, but no arrangements are in place to assure their long-term preservation.


Check out today’s posting at the National Security Archive’s Nuclear Vault – http://www2.gwu.edu/~nsarchiv/nukevault/ebb459/

Find us on Facebook – http://www.facebook.com/NSArchive

Unredacted, the Archive blog – http://nsarchive.wordpress.com/


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THE NATIONAL SECURITY ARCHIVE is an independent non-governmental research institute and library located at The George Washington University in Washington, D.C. The Archive collects and publishes declassified documents acquired through the Freedom of Information Act (FOIA). A tax-exempt public charity, the Archive receives no U.S. government funding; its budget is supported by publication royalties and donations from foundations and individuals.

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