Six very large nuclear tests were conducted at the Bikini Atoll and the Enewetak Atoll as part of Operation Castle in 1954 . The most notable was Castle Bravo , which was the first deployable ( dry fuel ) hydrogen bomb developed by the United States . Its yield , at 15 Mt , was over twice as powerful as was predicted , and remains the largest weapon ever detonated by the United States . It spread nuclear fallout over a wide area , including the Enewetak Atoll , Rongerik Atoll , Ailinginae Atoll , and Rongelap Atoll . The U.S. Navy evacuated the islanders within the next few days , but many of the natives exposed suffered from cancers and a high incidence of birth defects in the years following the event . The fishermen aboard the Japanese fishing vessel , the '' Daigo Fukuryu Maru '' , were additionally exposed and one man died soon after from complications of radiation sickness , resulting in considerable international controversy
Castle Bravo
Castle Bravo
Pacific Proving Grounds