In the 1960s and early 1970s, U.S. policymakers maintained a complex effort to limit the dissemination of gas centrifuge technology for enriching uranium, which they saw as an inherent nuclear proliferation risk. Recognizing that controls could not stop scientific research and development, U.S. officials nevertheless believed the overseas development of gas centrifuge technology could be slowed. To prevent further dissemination overseas, the United States supported cooperation with European allies that were already developing the technology. Cooperation involved implementation of secrecy and export controls, although a U.S. initiative to include Japan failed because nuclear secrecy was incompatible with Japanese law. The United States tried to deflect Japan's interest in the gas centrifuge by offering to share an alternative technology, gaseous diffusion, for enrichening uranium. That initiative failed, but the U.S. government remained committed to keeping enrichment technologies under secrecy controls.