was a series of above-ground test nuclear detonations carried out by the U.S. in 1954. They took place at the Pacific Proving Grounds on Bikini
and Eniwetok Atoll
s. The most memorable shot was the second ('Castle Bravo') detonation.
This thermonuclear explosion contaminated a vast swath of the Pacific, with fallout reaching the inhabited Marshall Islands. A Japanese fishing trawler (the Fifth Lucky Dragon) was caught in the fallout region; several of the 23 crew died of radiation poisoning.
The Castle Bravo shot was a surprise for those who designed and fired it. It had been expected to produce a yield of approximately 3 megatons - however it produced one of 15. Sadly, it appears that there is evidence that the U.S. Military knew the weather conditions before the shot, and in fact noted that it might contaminate the Marshall Islands in the wind's path, but went ahead with the test anyhow. Although it doesn't excuse them, the fact that the test was 5 times the yield predicted meant that the fallout levels and spread pattern were much, much larger than had been forecast.