Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946 . They were the first nuclear weapon tests since Trinity in July 1945 , and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9 , 1945 . The purpose of the tests was to investigate the effect of nuclear weapons on warships
Trinity
Trinity (nuclear test)
Operation Crossroads