Conant mentioned the thermonuclear and asked Oppenheimer what gestation period that much more violent mechanism would require; Oppenheimer estimated a minimum of three years. The Los Alamos director took the floor then to review the explosive forces involved. First-stage bombs, he said, meaning crude bombs like Fat Man and Little Boy, might explode with blasts equivalent to 2,000 to 20,000 tons of TNT. That was an upward revision of the estimate Bethe had supplied the Target Committee at Los Alamos in mid-May. Second-stage weapons, Oppenheimer went on—meaning presumably advanced fission
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