the Soviet Union in August 1949 came earlier than Americans expected, and over the next several months there was an intense debate within the U.S. government, military, and scientific communities over whether to proceed with the development of the far more powerful, nuclear fusion-based hydrogen bomb, then known as "the Super". Oppenheimer had been aware of the possibility of a thermonuclear weapon since the days of the Manhattan Project and had allocated a limited amount of theoretical research work toward the possibility at the time, but nothing more than that, given the pressing need to develop a fission weapon. Immediately following the end of the war, Oppenheimer argued against continuing work on the Super at that time, due to both lack of need and the enormous human casualties that would result from its use. Now in October 1949, Oppenheimer and the GAC recommended against the development of the Super. He and the other GAC members were motivated partly by ethical concerns, feeling that such a weapon could only be strategically used, resulting in millions of deaths: "Its use therefore carries much further than the atomic bomb itself the policy of exterminating civilian populations." They also had practical qualms, as there was no workable design for a hydrogen bomb at the time. Regarding the possibility of the Soviet Union developing a thermonuclear weapon, the GAC felt that the United States could have an adequate stockpile of atomic weapons to retaliate against any thermonuclear attack. In that connection, Oppenheimer and the others were concerned about the opportunity costs that would be incurred if nuclear reactors were diverted from materials needed for atom bomb production to the materials such as tritium needed for a thermonuclear weapon. A majority of the AEC subsequently endorsed the GAC recommendation, and Oppenheimer thought that the fight against the Super would triumph, but proponents of the weapon lobbied the White House vigorously. On January 31, 1950, Truman, who was predisposed to proceed with the development of the weapon anyway, made the formal decision to do so. Oppenheimer and other GAC opponents of the project, especially James Conant, felt disheartened and considered resigning from the committee. They stayed on, though their views on the hydrogen bomb were well known. In 1951, Edward Teller and mathematician Stanislaw Ulam developed what became known as the Teller-Ulam design for a hydrogen bomb. This new design seemed technically feasible and Oppenheimer officially acceded