Nuclear fission Mexico, which was the scientific hub for research on bomb development and design. Other sites, notably the Berkeley Radiation Laboratory and the Metallurgical Laboratory at the University of Chicago, played important contributing roles. Overall scientific direction of the project was managed by the physicist J. Robert Oppenheimer. In July 1945, the first atomic explosive device, dubbed "Trinity", was detonated in the New Mexico desert. It was fueled by plutonium created at Hanford. In August 1945, two more atomic devices – "Little Boy", a uranium-235 bomb, and "Fat Man", a plutonium bomb – were used against the Japanese cities of Hiroshima
Nuclear arms race on Bikini Atoll. Scientists significantly underestimated the size of the bomb, thinking it would yield 5 megatons. However, it yielded 14.8 megatons, which is the largest nuclear explosion tested by the U.S. The explosion was so large the nuclear fallout exposed residents up to 300 miles away to significant amounts of radiation. They were eventually evacuated, but most of them experienced radiation poisoning and resulted in one death from a crew member of a fishing boat 90 miles from the explosion. The Soviet Union detonated its first "true" hydrogen bomb on November 22, 1955, which had a yield of 1.6