 As much of the Manhattan Project data leaked by the spies Klaus Fuchs , Theodore Hall , and David Greenglass to the Soviet Union concerned Fat Man , the Soviet Union 's first nuclear weapon , designated " Joe @-@ 1 " by the United States , was based closely on Fat Man 's design . " Joe 1 " was detonated on 29 August 1949 as part of Operation " First Lightning " . 
