The global spread of advanced military armaments can be usefully characterized as a diffusion process, defined as the communication of innovations among the units of a social system over time. But what causes innovations in military technology to diffuse across the international system? The answer to this seemingly basic question is critically important to any understanding of the spread of arms. Despite this, it is rarely posed or addressed in so general and direct a manner. Scholars and policy analysts have written volumes of specific case studies on arms exporters, arms importers, and categories of military technologies. These studies usually contain numerous implicit and explicit explanations of why nations acquire armaments. Many descriptive and prescriptive overviews of the arms trade also attempt to explain the rationale behind arms transfers. However, there have been few if any empirical studies which attempt to systematically measure the rate of the spread of specific arms technologies across the international system as a whole. Fewer still then use this data to test theoretical causal hypotheses. This project attempts to fill this gap in our understanding of the arms proliferation phenomenon.