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.
Rongelap Atoll
From 1946 through 1958 the United States military conducted numerous atmospheric nuclear weapons tests, including hydrogen bomb tests, primarily at Bikini Atoll, about from Rongelap Atoll. On March 1, 1954, the testing of the Castle Bravo hydrogen device produced an explosion that was 2½ times more powerful than predicted, and produced unexpected amounts of fallout that resulted in widespread radioactive contamination. The blast cloud contaminated more than of the surrounding Pacific Ocean including some of the then inhabited surrounding islands including Rongerik Atoll, Rongelap Atoll ( away) and Utirik Atoll.