Why do countries want nuclear weapons? This question has plagued non- proliferation and U.S. intelligence experts since the beginning of the nuclear era. Motivations for nuclear weapons typically are viewed as the product of external variables (perceived insecurity, prestige, etc.). This thesis asserts that a different level of analysis is appropriate. It is a society's beliefs about nuclear technology that at least partially explains nuclear proliferation. The 1939 U.S. decision to develop nuclear weapons is examined in light of early American beliefs about nuclear technology. I show that various cultural texts and statements by influential elites made policy makers believe in the military utility of nuclear energy. If these texts and statements had not existed, President Roosevelt might not have launched the Manhattan Project.