Operation Castle 1954

Six tests. Bravo (15 Mt) was the largest nuclear test ever conducted by the United States — 2.5x the expected yield. The error caused catastrophic radiological contamination: a Japanese fishing boat (Daigo Fukuryu Maru) was irradiated, crew members died, and widespread fallout rained on inhabited atolls. The Bravo shot yielded 1,000 Hiroshimas.

Castle Bravo's fallout poisoned the people of Rongelap and Utirik and the crew of the Lucky Dragon, galvanizing the global movement that would lead to the 1963 atmospheric test ban.