How do states build their nuclear forces? What about the global nuclear non-proliferation regime allows states to proliferate the means of nuclear delivery? Most studies of nuclear proliferation explain why states build the nuclear bomb and how they do it. What they miss, however, is how states develop the wherewithal to deliver these nuclear weapons – a crucial part of operationalizing any nuclear force. My dissertation posits an original framework to understand how states build the forces to deliver their nuclear weapons. It addresses the empirical puzzle of why the non-proliferation order – instead of constraining the spread of the means of nuclear delivery – enables it. I argue that there exists a Zone of Ambiguity in this order that consists of definitional ambiguity, multipurpose technology, and an indeterminate legal and normative framework. This Zone creates a permissive environment for the transfer of technology related to the means of nuclear delivery through three enabling logics. Each of these logics – economic, geopolitical, and alliance-related – highlight different political interests that states have in proliferating nuclear delivery vehicles. To demonstrate the argument, I conduct historical case studies based on the nuclear force development of three states – the United Kingdom, France, and India. I use newly declassified material from the archives of multiple states to bring forward new historical evidence and uncover an international history of the development of nuclear forces. In the process, I also trace the historical trajectory of the evolution of the global nuclear non-proliferation regime as it relates to the means of nuclear delivery.