How and why do nuclear delivery vehicles proliferate? This talk identifies a permissive environment for the proliferation of nuclear delivery systems in the international nuclear non-proliferation regime. There are three drivers of this dynamic: First, the multipurpose/dual-use nature of the technology to deliver nuclear weapons; second, the definitional obscurity in the non-proliferation regime about what constitutes a 'nuclear weapon'; and third, the exclusion of legally-enforceable legislation on delivery systems in the nuclear non-proliferation regime. I identify the different pathways of proliferation that both supplier and recipient states use to take advantage of these enabling factors to acquire/disseminate nuclear delivery vehicles. Using qualitative historical evidence from archives across the United States, the United Kingdom, France, and India, l use an international history approach to trace the trajectory of the nuclear non-proliferation regime's regulation of nuclear delivery vehicles.