 Neddermeyer discarded Serber and Tolman 's initial concept of implosion as assembling a series of pieces in favor of one in which a hollow sphere was imploded by an explosive shell . He was assisted in this work by Hugh Bradner , Charles Critchfield , and John Streib . L. T. E. Thompson was brought in as a consultant , and discussed the problem with Neddermeyer in June 1943 . Thompson was skeptical that an implosion could be made sufficiently symmetric . Oppenheimer arranged for Neddermeyer and Edwin McMillan to visit the National Defense Research Committee 's Explosives Research Laboratory near the laboratories of the Bureau of Mines in Bruceton , Pennsylvania ( a Pittsburgh suburb ) , where they spoke to George Kistiakowsky and his team . But Neddermeyer 's efforts in July and August at imploding tubes to produce cylinders tended to produce objects that resembled rocks . Neddermeyer was the only person who believed that implosion was practical , and only his enthusiasm kept the project alive . 
