Ongoing nuclear modernization programs in Russia, China, and the USA have reopened longstanding debates among scholars concerning whether tailored nuclear weapons are likely to have destabilizing consequences for international security. Without data to adjudicate this debate, however, these discussions have remained entirely theoretical. In this article, we introduce an experimental wargaming platform, SIGNAL, to quantify the effect of tailored nuclear capabilities on the nuclear threshold in a simulated environment. We then compare these results with a survey experiment using scenarios related to military basing, cyber operations, and nuclear threats from the wargame environment. While the survey experiments suggest that the presence of tailored nuclear capabilities increases the likelihood of conflict escalation, this trend diminishes in the wargaming context. Across both data-generating processes, we find support for the proposition that lower-yield nuclear weapons are used as a substitute for their higher-yield counterparts. These results have consequences for recent and ongoing policy debates concerning strategic posture and the future of arms control. This work also makes methodological contributions to the design and application of experimental wargaming for social science research, particularly for scenarios where data are limited or non-existent.

With the continued use of unsafeguarded naval nuclear-propulsion programs in all nuclear-weapon states, the commissioning of an Indian nuclear submarine, and the potential investment in such programs by non-nuclear-weapon states including Brazil and South Korea, movement toward a regulatory regime for nuclear material in the naval sector has become imperative. Such a framework faces a recurring debate on adequately protecting sensitive military technology while delivering assurances that naval nuclear material is not diverted to nuclear-weapon programs. In this viewpoint, we examine various prospective mechanisms to regulate naval nuclear stocks and assess them in terms of their effectiveness and scope. Drawing on lessons from the drafting, negotiation, and implementation of the Model Additional Protocol, we recommend a safeguards regime for naval nuclear material via a protocol that supplements the existing global nuclear-governance system. This protocol provides a standardized yet flexible approach to naval nuclear-material safeguards across all states (whether nuclearweapon states, non-nuclear-weapon states, or outside the Treaty on the Non-Proliferation of Nuclear Weapons) to handle variations among naval nuclear fuel cycles and technologies.

Technology enables new research designs, and more data

National security decisions are driven by complex, interconnected contextual, individual, and strategic variables. Modeling and simulation tools are often used to identify relevant patterns, which can then be shaped through policy remedies. In the paper to follow, however, we argue that models of these scenarios may be prone to the complexity-scarcity gap, in which relevant scenarios are too complex to model from first principles and data from historical scenarios are too sparse - making it difficult to draw representative conclusions. The result are models that are either too simple or are unduly biased by the assumptions of the analyst. We outline a new method of quantitative inquiry - experimental wargaming - as a means to bridge the complexity-scarcity gap that offers human-generated, empirical data to inform a variety of model and simulation tasks (model building, calibration, testing, and validation). Below, we briefly describe SIGNAL - our first-of-a-kind experimental wargame designed to study strategic stability in conflict settings with nuclear weapons. We then highlight the potential utility of this data for modeling and simulation efforts in the future using this data.

States facing the decision to develop a nuclear weapons program do so within a broader context of their relationships with other countries. How these diplomatic, economic, and strategic relationships impact proliferation decisions, however, remains under-specified. Adding to the existing empirical literature that attempts to model state proliferation decisions, this article introduces the first quantitative heterogeneous network analysis of how networks of conflict, alliances, trade, and nuclear cooperation interact to spur or deter nuclear proliferation. Using a multiplex network model, we conceptualize states as nodes linked by different modes of interaction represented on individual network layers. Node strength is used to quantify factors correlated with nuclear proliferation and these are combined in a weighted sum across layers to provide a metric characterizing the proliferation behavior of the state. This multiplex network modeling approach provides a means for identifying states with the highest relative likelihood of proliferation—based only on their relationships to other states. This work demonstrates that latent conflict and nuclear cooperation are positively correlated with proliferation, while an increased trade dependence suggests a decreased proliferation likelihood. A case study on Iran’s controversial nuclear program and past nuclear activity is also provided. These findings have clear, policy-relevant conclusions related to alliance posture, sanctions policy, and nuclear assistance.