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.
Bokak Atoll
While en route from the US to Asia in April, 1953, LST 1138, later commissioned as , dropped anchor at Bokak to search for rumored Japanese stragglers. The landing party noted the remains of the wartime outpost, but found no signs of any current occupants.
In 1954, the experience of large scale fallout from the Castle Bravo nuclear test on Bikini Atoll led to a pre-planned aerial survey of atolls adjacent to the subsequent Castle Romeo test, timed at one and four hours after the shot. The aircraft were equipped with gamma radiation detectors designed to measure ground contamination from altitudes of . An overflight of Sibylla Island measured 1.0 mrem/hr (10 μGy) an hour after the shot, dropping to 0.4 mrem/hr (4 μGy) three hours later. In 1957, Bokak was surveyed as a site for nuclear weapons testing as a part of Operation Hardtack, but due the number of improvements required to develop it, was passed over in favor of reusing the Bikini, Enewetak, and Nevada test sites. The atoll came under renewed consideration for use during Operation Dominic, but by that time the potential for political fallout from nuclear testing within a United Nations Trust Territory was deemed too great.