Castle Bravo
Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of "Operation Castle". Detonated on March 1, 1954, the device was the most powerful nuclear device detonated by the United States and its first lithium deuteride fueled thermonuclear weapon. Castle Bravo's yield was 15 megatons of TNT, 2.5 times the predicted 6.0 megatons, due to unforeseen additional reactions involving Li, which led to the unexpected radioactive contamination of areas to the east of Bikini Atoll.
Castle Bravo
The US Navy tanker was at Enewetak Atoll in late February 1954. "Patapsco" lacked a decontamination washdown system, and was therefore ordered on 27 February, to return to Pearl Harbor at the highest possible speed. A breakdown in her engine systems, namely a cracked cylinder liner, slowed "Patapsco" to one-third of her full speed, and when the Castle Bravo detonation took place, she was still about 180 to 195 nautical miles east of Bikini. "Patapsco" was in the range of nuclear fallout, which began landing on the ship in the mid-afternoon of 2 March. By this time "Patapsco" was 565 to 586 nautical miles from ground zero. The fallout was at first thought to be harmless and there were no radiation detectors aboard, so no decontamination measures were taken. Measurements taken after "Patapsco" had returned to Pearl Harbor suggested an exposure range of 0.18 to 0.62 R/hr. Total exposure estimates range from 3.3 R to 18 R of whole-body radiation, taking into account the effects of natural washdown from rain, and variations between above- and below-deck exposure.