Chapter [II — The Bravo Accident “Bravo’, the first atomic test in the Castle series. was a large thermonuclear device detonated on the reef at Bikin: Atoll on March 1. 1954. An unexpected shift in winds caused an unprecedented accidental fallout. Two hundred and thirty-nine Marshallese on Rongelap, Ailingnae, and Utirik Atolls. 28 American ser- vicemen on Rongerik Atoll, and 23 Japanese fishermen on their ship, the Lucky Dragon, received significant exposure to radioactive fallout. At midnight the weatherstill held, but low altitude winds now light and vari- able raised chancesof fallout in the wrong piace. Bikini’s weather outlook was downgraded to unfavorable, and the task force ordered its ships 50 miles further out to sea. Assuming the worst, some winds might blow toward the nearest inhabited atolls, but predicted speeds and altitudes seemed to preclude any real danger: debris could reach Rongelap or Rongerik only after 12 to 15 hours, by then having decayed to safe levels. Two hours before shot time the earlier forecast remained valid. Task force commander Clarkson confirmed his orderto fire at 06:45. piKIN' a -- AILINGINAE. 7 RONGELAP . S yTIRIK , 5 * . Winds high aloft carried the radioactive cloud . a < \ KWAJALEIN . 9 , in an easterly direction, depositing seriously high fallout on a Japanese fishing vessel and on 2 the inhabited atolls of Rongelap, Ailingnae, 9 oa ° 9 mauRO To wT _ The actualyield of the detonation was considerably more than expected, a surprising 15 megatons (almost one thousand timesthe yield of the bombs over Hiroshima and Nagasaki). Rongerik, and Utirik. Several naval vessels, thirty miles east of Bikini, unexpectedly encountered heavyfallout with white flakes falling on the decks of the ships. Top-speed retreat was ordered and, with crews below decks andsalt water washing down on the decks, the-hazard was greatly reduced. (Later, several sailorsdeveloped. mild radiation burns ofthe skin.) 2... : ae eaepeingeee re Fallout ares in the Marshall Islands.“« - tM The realizationofthe. extensivenessof the fallout in the area edatof Bikini emerged slowly . because ofiaseries of confusing and overlapping © events. Difficulties were encountered with the cloud-tracking planes and there was confusion A. Early Events Most of the following events were excerpted from Barton C. Hacker’s report: Elements of Controversy: A History ofRadiation Safety in the Nuclear Testing Program (B-6). As was usual, numerous meteorological observations were madeto insure that the about the radiological situation on Rongerik atoll, where 28 American servicemen manned a radiological safety weather station. On Rongerik, a blast wavehit the island and shook the buildings about eleven minutes . radioactive cloud from the detonation would not movein the direction of the inhabited atolls to the east. * 2 ~~ Tp ee ee ee oes ee amy proumn alrr Qoe a a 7 a aewe tee a —a - eo ele me -- after the men had observed the flash from the detonation. About four to six hourslater, a mist-like haze was noted. At seven hours, the needle on a radiation- measuring instrument went off scale at 100 plus mr/hr. The Task Force