The gas centrifuge revolutionized uranium processing for nuclear power, but it also enabled countries to make nuclear weapons more easily. It is widely known that the Manhattan Project failed to make a viable centrifuge; the first successful machines were produced in the 1950s by German prisoners of war in the Soviet Union. Little has been written about what it took to perfect the device or why it became the proliferation machine it is today. This article traces its development by exploring the role of technological change, tacit knowledge, and secrecy. This history argues that, contrary to popular understanding, constructing basic centrifuges has never been cutting-edge or resource-intensive. This breaks with the Manhattan Project mythology that nuclear weapons require techno-industrial greatness. Consequently, technology-based nonproliferation policies flowing from such thinking were arguably misinformed; it is likely that nuclear proliferation has been, or will be, controlled more by motivations than by technological constraints.