The Castle Bravo hydrogen bomb test went badly wrong
On this day · 1 March 1954
On this day in 1954, America's largest nuclear test exploded at nearly triple its predicted force, scattering fallout across the Pacific.
On March 1, 1954, the United States detonated Castle Bravo at Bikini Atoll in the Marshall Islands, its largest nuclear test ever. Planners expected about 6 megatons. The device delivered 15, roughly 1,000 times the Hiroshima bomb, because they had badly underestimated how much energy the lithium-7 in its fuel would release.
The oversized blast vaporized millions of tons of coral and seawater, hurling a radioactive cloud some 100 miles wide downwind. Fallout dusted the inhabited atolls of Rongelap and Utirik, whose residents were evacuated only after days of exposure, and showered the Japanese fishing boat Lucky Dragon No. 5, sickening its crew and killing one man.
The explosion was more than two and a half times greater than expected.
The accident triggered an international outcry, fueled fears about thermonuclear weapons, and left a legacy of contamination and displaced communities that endures in the Marshall Islands today.
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