Findings

This study yields nine core findings.

1. Disagreement over the nuclear-armed sea-launched cruise missile (SLCM-N) reflects competing mental models, not disputed facts. Expert disagreement is driven less by different assessments of SLCM-N’s technical performance or force structure than by divergent underlying models of deterrence, escalation, and risk. Confidence-, Caution-, and Contingent-oriented experts often reference the same strategic trends—such as Chinese nuclear expansion and the concerns of South Korea and Japan—but reach opposing conclusions because they reason from different assumptions about adversary behavior, crisis dynamics, and escalation control. As a result, debates over SLCM-N persist even when factual premises largely converge.

2. SLCM-N’s value is conditional, not intrinsic. Across the four futures examined, SLCM-N proves decisive only in a narrow set of conditions. It matters most when U.S. resolve is actively contested and escalation dynamics remain relatively predictable—specifically, given a more assertive U.S. posture and steady technological change. In more benign environments, SLCM-N adds little marginal value; in highly disruptive environments, it can increase misperception and escalation risk. No future supports a claim that SLCM-N is either categorically stabilizing or categorically destabilizing.

3. How U.S. actions are interpreted matter as much as what capabilities are deployed. Across interviews and scenarios, outcomes are shaped less by the presence of SLCM-N than by how adversaries—particularly China—interpret U.S. intent. The same deployment can deter coercion and reassure allies in one future while provoking arms racing or escalation in another. This finding reinforces a practical lesson: Posture choices cannot be evaluated independently of how they are read by others. Declaratory policy, signaling, and communication strategy therefore shape escalation risk as much as hardware.

4. U.S. nuclear posture tracks the pace of technological change. Forecasting results show that the two most likely futures sit diagonally from one another: Assertive Stability (steady technological change with a more assertive U.S. posture) and Adaptive Deterrence (disruptive technological change with a more defensive posture). This pattern indicates that experts do not view technological change and U.S. posture as independent drivers. When technological change is steady, leaders feel more confident in escalation dynamics and signaling, making offensive nuclear posture appear manageable. When technological change is disruptive, uncertainty pushes the United States toward defensive nuclear strategy.

5. Experts judge Adaptive Deterrence as the most likely future in 2035. The most likely future is characterized by disruptive technological change combined with a U.S. posture perceived as defensive. Interestingly, Adaptive Deterrence is not the future where SLCM-N has the greatest utility.

6. The Indo-Pacific is where SLCM-N’s effects matter most—and where risks concentrate. Experts broadly agree that SLCM-N has greater potential relevance in the Indo-Pacific than in Europe given maritime geography, the lack of forward-deployed U.S. nuclear weapons, and alliance assurance dynamics involving Japan and South Korea. Forecasts indicate a meaningful probability of large-scale Chinese military action against Taiwan alongside a low likelihood of explicit nuclear threats or an abandonment of China’s No First Use policy. This combination suggests that escalation risks are driven primarily by conventional conflict dynamics rather than immediate nuclear signaling. U.S. policy should therefore prioritize crisis management, early-warning coordination with allies, and avoiding posture changes that heighten Chinese threat perceptions during conventional crises.

7. Alliances and norms remain the strongest stabilizing force. Experts consistently assessed NATO cohesion and allied nonproliferation as durable across most futures, with low probabilities of alliance fracture or allied nuclear proliferation. Importantly, these assessments were made before the recent tensions over Greenland and the end of the New START arms reduction treaty. While the forecasts suggest that alliance stability is robust under baseline conditions, the analysis also indicates that risks rise significantly in futures marked by more offensive state behavior, a pattern recent developments may help illuminate.

8. SLCM-N is a contested and highly conditional bargaining chip for future arms control. Experts were divided on whether SLCM-N would provide meaningful leverage in future arms control negotiations. Some viewed it as a potential negotiating chip that could be traded for limits on nonstrategic nuclear weapons or emerging systems, particularly if broader arms control frameworks are revived. Others argued that its value as a bargaining chip is limited by verification challenges, its role in alliance assurance, and the risk that giving it up would yield little reciprocal restraint. Additionally, SLCM-N effects in the four futures indicate that its bargaining value could depend on timing and context: It may be tradable in an environment of bounded competition and credible arms control, but it risks undermining deterrence and assurance if it’s used for bargaining in more competitive conditions.

9. Resumed U.S. nuclear testing would have grave consequences. Our scenario planning phase showed that any U.S. test—regardless of yield—would carry disproportionate signaling consequences, affecting global norms, alliance confidence, and competitor threat perceptions, and could prompt reciprocal testing by China or Russia. Decisions about testing should therefore be evaluated primarily as strategic signals rather than as technical measures.

The findings above carry several implications for U.S. nuclear policy and force planning.

1. The nuclear-armed sea-launched cruise missile (SLCM-N) should be treated as a hedge, not a fix. Our analysis does not support treating SLCM-N as a cornerstone of extended deterrence or a singular response to perceived deterrence gaps. Its contribution is contingent and time-bound. Overreliance on the system risks crowding out attention to broader posture, signaling, and alliance-management challenges that ultimately determine credibility.

Because SLCM-N’s relevance varies across strategic conditions, decisions about its development, deployment, and signaling should be tied to observable indicators rather than treated as a static requirement. Policymakers should focus in particular on:

• Whether adversary perceptions of U.S. escalation options are narrowing
• Whether technological trends undermine air-delivered or dual-capable systems
• Whether Russia integrates U.S. sea-based systems into force-planning narratives
• Whether Chinese nuclear signaling becomes more explicit or assertive

Adjusting SLCM-N development or deployment in response to these indicators would allow the United States to manage uncertainty without overcommitting to a capability that may have limited relevance in more stable futures.

2. Concept of operations (CONOPS) ambiguity is now a strategic variable. Unresolved questions about deployment patterns, visibility, commingling with conventional payloads, and command-and-control procedures are not merely technical. They will shape how SLCM-N is interpreted and therefore how it affects stability. Leaving these questions unresolved increases the risk that the system’s effects will be driven by adversary inference rather than U.S. intent.

3. Modernization interactions matter more than individual systems. SLCM-N will emerge alongside long-range standoff weapons (LRSO), the B-21 bomber, low-yield submarine-launched ballistic missiles (SLBMs), missile-defense developments, and possible testing decisions. Its impact will be cumulative, not discrete. Policymakers should therefore evaluate SLCM-N as part of an evolving portfolio rather than in isolation, especially given how adversaries aggregate signals across systems.

4. Alliance assurance is poorly specified but strategically decisive. Throughout this project, “assurance” functions as a shorthand rather than a clearly articulated requirement. Allies appear reassured by the existence of capability but uncertain about its meaning, employment, and implications. This ambiguity can stabilize or destabilize depending on context. Without a clearer understanding of what allies actually find reassuring, SLCM-N risks becoming a symbolic substitute for sustained political engagement.

5. China’s interpretation is the central crux point. Across all futures, China’s response functions as the decisive crux point. Whether SLCM-N stabilizes or destabilizes depends less on U.S. intent than on Beijing’s beliefs about U.S. escalation thresholds, warfighting concepts, and confidence in defenses. Monitoring Chinese doctrinal signals and perception shifts is therefore as important as tracking the system’s technical development.

Based on these findings and implications, the report offers seven recommendations aimed at improving nuclear decision-making amid deep uncertainty.

1. Plan for sustained nuclear competition with China and Russia. Expert forecasts show a strong consensus that we should expect Chinese nuclear expansion and ongoing Russian doctrinal adaptation. These developments represent a durable trend toward a more contested nuclear environment even under otherwise stable geopolitical conditions. Policymakers should expect pressure on extended deterrence, increased signaling risks, and narrower margins for misinterpretation in crises. This trend strengthens the importance of flexible, resilient force options but also elevates the need for disciplined communication and transparency to prevent unintended escalation.

2. Treat technological disruption as a source of uncertainty, not a prediction. Experts do not agree on whether disruptive technologies—such as improved submarine sensing, advanced missile defense, or novel intelligence, surveillance, and reconnaissance (ISR) capabilities—will decisively transform the military balance, even as many anticipate increasing technological pressure on existing deterrence assumptions. Policymakers should therefore avoid planning anchored to assumptions of either continuity or imminent, system-wide disruption. Instead, force design should prioritize modularity, platform diversity, and hedging options that mitigate the risk of surprise. Investments that reduce reliance on any single survivability assumption (undersea, airborne, or space-based) are most robust across the range of futures identified.

3. Stress-test the nuclear-armed sea-launched cruise missile (SLCM-N) across futures before committing to a scale or posture. Rather than assuming a single future, policymakers should evaluate how different deployment choices perform across the four possible worlds. This approach identifies where SLCM-N is robust, where it is fragile, and where mitigating measures are required.

4. Link SLCM-N development and deployment to observable indicators. Decisions about numbers, visibility, and employment should be tied to indicators such as adversary signaling behavior, technological developments affecting survivability, and alliance confidence trends. This enables an adaptive posture rather than a static commitment.

5. Clarify concept of operations (CONOPS) early to shape perception. Even if some ambiguity is retained, the United States should articulate internally coherent concepts of operation and externally consistent messaging. Allowing adversaries to infer intent from silence increases the risk of worst-case interpretation.

6. Invest in alliance consultation as a stabilizing mechanism. Allies differ in how they interpret ambiguity, visibility, and escalation risk. Tailored consultation, rather than uniform messaging, will better align expectations and reduce crisis miscalculation.

7. Make underlying mental models explicit in policy deliberations using futures tools. Policy discussions should explicitly surface the assumptions driving expert advice and recommendations. Doing so clarifies whether disagreements stem from facts or from competing theories of escalation and deterrence, reducing circular debates and improving analytic rigor. Futures tools—such as forecasting, scenario planning, red teaming (mimicking real-world threats), pre-mortems, and competing hypothesis analysis—can help expose untested assumptions embedded in expert judgments. This process clarifies risks and improves policy resilience.

This study shows that disagreements over the nuclear-armed sea-launched cruise missile (SLCM-N) stem less from disputes over evidence than from fundamentally different assumptions about how deterrence works, how crises unfold, and how adversaries respond to U.S. actions.

Two research-relevant implications follow.

1. Additional evidence alone is unlikely to resolve policy disagreement. Because experts weigh risks differently and prioritize different failure modes, new technical analyses or capability comparisons tend to reinforce existing positions rather than create consensus. What appears to be a factual disagreement is often a disagreement about which risks matter most and which can be managed. Research that treats disagreement as an information gap risks missing the real sources of contention.

2. Mental models act as “hidden drivers” of expert recommendations and positions. The Confidence, Caution, and Contingent Models identified in the study produce consistent differences in how experts evaluate ambiguity, flexibility, and restraint. Policymakers assessing expert advice therefore need to understand which model a recommendation reflects to understand why it is being made.

Each mental model privileges certain risks and downplays others. For example:

• The Confidence Model may underweight misinterpretation risks.
• The Caution Model may overstate the escalatory impact of marginal posture changes.
• The Contingent Model may underestimate moments when clarity and commitment become decisive.

Making these tendencies explicit helps identify where planning and analysis may be skewed. These implications point to several research extensions that would improve policy-relevant understanding of SLCM-N and nuclear risk more broadly.

3. Scenario-driven war-gaming of SLCM-N in crisis and conflict. A direct continuation of this project would adapt the four futures into war games that would force participants to make concrete choices about deployment, signaling, and escalation under time pressure. This would clarify when SLCM-N meaningfully alters outcomes, when it does not, and which assumptions about adversary behavior drive those judgments.

4. A focused study of alliance assurance requirements and/or track II dialogues (which are informal discussions among former officials, experts, and academics intended to explore sensitive issues outside official diplomatic channels). Throughout this report, “assurance” often functions as shorthand for a complex and poorly specified set of allied expectations. A focused follow-on study or track II dialogues could examine what allies—particularly Japan and South Korea—actually find reassuring or destabilizing, how nuclear versus non-nuclear signals are interpreted, and whether SLCM-N contributes directly to confidence or merely signals U.S. presence. This would replace assumption-driven reasoning with empirically grounded insight that would strengthen both alliance management and force-planning decisions.

5. Longitudinal forecasting to track shifts in expert beliefs. A natural extension of our project’s forecasting effort would be a study in which the same cohort of experts periodically revisits its judgments as geopolitical conditions, technologies, and doctrines evolve. Iterated elicitation would allow researchers to observe how beliefs update over time, which indicators drive reassessment, and where consensus hardens or fragments. Such a study would create a dynamic risk-tracking capability directly relevant to long-term posture planning.

Beyond these core potential research extensions, several additional lines of inquiry could address persistent analytical gaps, including:

• How Chinese and Russian strategists interpret specific U.S. posture changes
• How emerging technologies compress decision time and affect escalation pathways
• How bureaucratic roles, civil-military relations, and domestic political incentives shape expert judgment and nuclear decisions