Project 4.1
In 1994, a 1953 "Castle Bravo" program prospectus was found which included reference to Project 4.1 apparently written before the "Bravo" shot had occurred. The U.S. government responded that someone had gone back into the project list after the "Bravo" test to insert Project 4.1; thus, according to the U.S. government, the acts were not premeditated. All other U.S. documents point to Project 4.1 having been established after the "Bravo" test—most sources point to its having been organized on March 7, 1954. The final Project 4.1 report began in its preface with the statement that "Operation CASTLE did not include a biomedical program" (it mentions this in discussing the ad hoc nature by which the project personnel were assembled). All official and mainstream historical accounts of the "Bravo" test indicate that its high level of fallout was a result of a miscalculation in relation to its design and was not deliberate (see the Castle Bravo article for more information on the alleged accident).
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.