This article discusses how West European governments reacted to U.S. efforts to control the emergence and spread of gaseous diffusion and ultracentrifuge technology for uranium enrichment. The article focuses on Dutch, British, and West German Cold War perspectives on nuclear technological cooperation with the United States. U.S. insistence on maintaining secrecy around the ultracentrifuge was driven not only by technological and nuclear nonproliferation concerns but also by overarching Cold War dynamics at the time of the 1961 Berlin crisis and NATO's nuclear modernization. The Dutch–West German exploration of bilateral nuclear cooperation on gas centrifuges and the subsequent U.S. classification efforts also reveal a story of transatlantic competition over technological ambitions, commercial interests, and Western Europe's strategic potential. The article thus highlights the intersection of the history of science and technology and Cold War diplomatic and nuclear history, combining fresh material from Dutch archives with U.S. and British primary sources.