Methodology

This project uses a structured three-phase approach to examine how expert judgments about the nuclear-armed sea-launched cruise missile (SLCM-N) change under different future conditions and to identify the uncertainties that most strongly shape assessments of whether the system would be stabilizing, destabilizing, or marginal in the 2030s.

First, we conducted in-depth interviews with a diverse set of experts, including proponents of SLCM-N, critics, and those with mixed views. These interviews focused on identifying the assumptions and mental models underlying expert judgments about SLCM-N’s purpose, deterrent effects, and risks. Interview data were systematically coded and mapped to reveal areas of convergence and disagreement, even when experts use similar language to justify opposing conclusions.

Second, we employed a scenario planning exercise set in the mid-2030s to test how judgments vary across different strategic environments. Rather than forecasting a single outcome, we explored how SLCM-N’s value and risks vary across four plausible futures generated by two high-impact uncertainties identified by experts: perceptions of the U.S. nuclear arsenal and the pace of technological change.

Finally, we incorporated expert probability assessments to identify early indicators of a shift in the strategic environment toward one future or another. This step provided a way to track directional change without implying prediction or false precision.

Together, these methods allow the analysis to inform policy choices despite deep uncertainty by clarifying which judgments are robust, which are contingent, and what developments would warrant reassessment.

We conducted 18 structured interviews with senior nuclear experts from think tanks and policymaking circles to examine the assumptions underlying their assessments of the security environment, nuclear escalation dynamics, and the utility of SLCM-N. These interviews were designed not only to capture substantive judgments but also to probe experts’ confidence in those judgments and the conditions under which those views might change. This approach enabled systematic comparison of where expert perspectives converged and where they diverged.

Interviews followed a common protocol of approximately 50 questions organized around three themes: (1) core assumptions and context dependencies, (2) key drivers and uncertainties, and (3) plausible future strategic environments.

To visualize patterns across respondents, we mapped experts into an “opinion space” based on the similarity of responses across interview questions (see Figure 1).¹ This visualization highlights clusters of shared assumptions as well as areas of disagreement, including cases in which experts reached different conclusions despite relying on similar underlying premises.

Experts positioned closer together expressed more similar assumptions and conclusions, while greater distance reflects more divergent perspectives.

Figure 2 uses hierarchical clustering to group experts based on similarity across the full set of coded variables. Experts who merge earlier in the tree share more closely aligned underlying judgments, while those whose branches connect later reflect deeper disagreement across multiple dimensions.

Interestingly, both the opinion-space map (Figure 1) and the hierarchical clustering (Figure 2) identify three distinct groups of experts. Though we initially expected two, those in favor of SLCM-N and those against, we also found a third group with more of a mixed or nuanced viewpoint.

Taken together, these belief patterns allow us to define three distinct “mental models,” defined as coherent frameworks of assumptions, priorities, and causal beliefs that experts use to interpret the security environment and evaluate policy choices. Group 1 aligns with a Confidence Model, emphasizing deterrence gaps, flexibility, and the stabilizing value of additional nuclear options such as SLCM-N. Group 2 reflects a Caution Model, prioritizing escalation risks, redundancy within existing forces, and the dangers of misperception or arms racing. Between these poles is Group 3, which corresponds to a Contingent Model: Experts in this group do not view SLCM-N as inherently stabilizing or destabilizing, instead assessing its value as highly dependent on future conditions, including technological change, adversary behavior, and the broader strategic context. This group draws selectively on elements of both Groups 1 and 2, helping to explain its intermediate position in the opinion space.

The Confidence Model: Flexibility and Assurance Benefit

Experts aligned with the Confidence Model view SLCM-N as a necessary tool for strengthening—and restoring—deterrence in regional conflict scenarios. Their core concern is adversary opportunism: They believe Russia or China may attempt limited, theater-level nuclear use precisely because they question whether the United States has credible, proportional response options at that level of conflict.

From this perspective, SLCM-N fills a critical gap. It provides a survivable, prompt, and precise response option that expands presidential choice without forcing an immediate leap to large-scale nuclear use (overwhelming escalation) or inaction (surrender). As one participant described the U.S. deterrence gap problem:

“[If] adversaries are losing a conventional war, they could use low-yield nuclear weapons within a specific theater to try to limit escalation. The Americans [would] have nothing to respond to in kind. They can’t go tit-for-tat or move one rung up the escalation ladder. The only options left are high-yield SLBMs [submarine-launched ballistic missiles], ICBMs [intercontinental-range ballistic missiles], or bombers—which [would be] already heavily tasked.”

A defining feature of the Confidence Model is its approach to risk. These experts do not deny escalation dangers, but they rank them below what they see as the greater threat: a deterrence posture that appears weak or constrained. In their view, deterrence fails not through inadvertent escalation but when adversaries perceive an opportunity to test U.S. resolve—particularly given Russia’s large nonstrategic nuclear arsenal and China’s rapid expansion. As one participant put it bluntly:

“[SLCM-N] enhances deterrence and is stabilizing because it increases escalation risks. It gives us the ability to escalate in response to adversary actions. I don’t see escalation itself as the problem; our ability to raise the level of violence is what gives [adversaries] pause, just like their weapons give us pause.”

Confidence Model experts also stress that SLCM-N’s flexibility derives not only from yield or promptness but also from how it can be deployed. Because it can be carried on attack submarines operating from international waters, SLCM-N allows the United States to shift capability across regions without overt basing decisions or visible force generation. One participant noted that the U.S. can “swing” Virginia-class submarines armed with SLCM-N to whichever part of the world the state leaders desire, choosing “exactly what effect [they] want the weapon to have.” Another participant agreed, saying: “Since seas are worldwide, SLCM-N can go worldwide.”

Non-visible generation is central to this logic. Unlike the air leg of the triad—which relies on visible alerting, forward basing, and host-nation approval—SLCM-N allows the United States to enhance military readiness without explicit signaling. If adversaries cannot observe when or where the capability is deployed, they must assume it could be available, increasing caution while reducing incentives for (and the likelihood of) preemption.

This emphasis on non-visible generation reflects a broader view within this group that strategic ambiguity is stabilizing—particularly in a political environment where adversaries themselves field dual-capable systems and commingle nuclear and conventional forces. As one expert explained:

“Ambiguity is a feature, not a bug. [SLCM-N] is meant to be ambiguous. Right now, [adversaries] know the answer: Every Virginia-class submarine out there does not have a nuclear weapon on board.”

Adherents of the Confidence Model argue that deterrence depends on capability and credibility. Credibility flows from visible demonstrations of strength—posture and political resolve—rather than from formal mechanisms or transparency. Strategic ambiguity is seen as a strength, not a liability, maintaining adversary caution and allied confidence. In this worldview, stability arises from mastery rather than elimination of risk. The idea is that danger, properly managed, can itself be a stabilizing force.

This endorsement of strategic ambiguity is the reason this group does not see SLCM-N’s dual-capable nature as destabilizing: Since adversaries cannot readily determine whether U.S. submarines carry nuclear or conventional payloads, they argue, their decision-making is complicated, inducing caution in a crisis. Several experts argued that SLCM-N’s dual-capable nature and its associated ambiguity could actually lower miscalculation risks compared with existing options. One expert suggested China is leveraging ambiguity similarly by integrating its conventional and nuclear forces: “China simply does not appear to be very concerned about separating its nuclear and conventional forces…In fact, [it] sees deterrent value in commingling those forces and maintaining dual-capable systems…They have to deal with that ambiguity and so do we.”

Another expert agreed, asking: “If the other guy is deploying dual-capable weapons systems, does he really care about ambiguity?”

Another key pillar of the Confidence Model is the role of SLCM-N in providing allied assurance, particularly in the Indo-Pacific. Experts frequently contrasted assurance in Asia with that in Europe, where roughly 100 U.S. B61 nuclear gravity bombs provide a visible, theater-level manifestation of extended deterrence. In Asia, they argued, no comparable forward-deployed nuclear option exists. A survivable, sea-based capability is therefore seen as essential to reinforcing U.S. commitments to Asian allies and reducing incentives for indigenous nuclear proliferation in countries such as South Korea and Japan. As one expert put the logic, “If you care about nonproliferation and the NPT [Treaty on the Non-Proliferation of Nuclear Weapons], we have to return American nuclear weapons to the Western Pacific.” Another expert stated that “renewed faith in the American umbrella is an anti-proliferant.”

Across these arguments, this group of experts expressed consistently high confidence in its assessments. They generally treated uncertainty as manageable and discounted escalation risks as secondary to what they saw as the greater danger of a weak deterrence posture—one that could encourage adversaries to test U.S. resolve and increase the risk of war.

As one expert conceded, deterrence may fail not due to miscalculation but because leaders consciously choose to challenge deterrence, believing they can absorb or manage the risks.

Confidence levels and openness to counterfactual scenarios are examined in detail in later sections of the report.

The Caution Model: Redundancy and Escalation Risks

Experts aligned with the Caution Model view SLCM-N as a marginal and largely redundant addition to U.S. deterrence—or, as one expert described it, “a solution in search of a problem”—that carries disproportionate escalation and misperception risks. Rather than identifying a clear deterrence gap, they argue that perceived weakness in U.S. deterrence stems from political commitment, communication, and signaling issues, not from the absence of a particular weapons system or hardware. One expert noted that “all the weapons in the world don’t fix the political problem,” while another emphasized the relative importance of soft power over hard: “Deterrence is credibility times capability; if either credibility or capability is zero, then deterrence is zero.” Another expert concluded, “The problem isn’t that we lack nuclear options. The problem is that adversaries question our political commitment.”

The United States, they argue, already possesses a wide range of nuclear options that span the spectrum of yield, delivery mechanism, survivability, and deployment plan. As one expert summarized, “We [already] have low-yield options. We have non-ballistic options. We have survivable options. We have deployed options.” In their view, the greater danger lies not in insufficient nuclear options but in misjudging how new capabilities interact with perception, escalation, and decision-making under stress. Any additional capability therefore must be evaluated not by its technical attributes alone but also by how it is perceived and interpreted by adversaries and allies.

A central concern within the Caution Model is escalation risk driven by misperception and entanglement. Because SLCM-N would be indistinguishable from conventional cruise missiles, it could blur the line between conventional and nuclear operations. In a crisis, adversaries may be unable or unwilling to wait to determine whether an incoming strike is nuclear or conventional. This ambiguity, they argue, incentivizes worst-case assumptions, increasing pressure to act first rather than risk losing retaliatory options. One expert warned, “That ambiguity could precipitate the sort of nuclear strike that you’re trying to avoid,” adding that “everybody thinks they can control escalation, but nobody can.”

Unlike experts aligned with the Confidence Model, those in the Caution Model reject the notion that strategic ambiguity is stabilizing in a crisis. While uncertainty may have deterrent value in theory, they argue that it has the opposite effect in a live crisis: Leaders expect the worst and plan accordingly. As one expert observed, “Ambiguity might sound stabilizing in theory, but not during a crisis—because during a crisis you expect the worst…If you’re an adversary and you see a sea-launched cruise missile coming at you, you don’t know whether it’s nuclear or conventional—and that uncertainty creates pressure to act first.” In this view, once nuclear weapons are already present in a theater, the distinction between conventional and nuclear payloads matters less than the fact that nuclear use is now conceivable.

More broadly, some experts contend that the introduction of SLCM-N itself adds risk by shaping adversary perceptions and prompting reactive behavior. Adding another low-yield nuclear system, they argue, risks reinforcing fears of preemption, lowering the perceived threshold for nuclear use and prompting reciprocal deployments in an action-reaction arms race. One expert noted that U.S. decision makers “don’t seem to think beyond 10 or 15 years,” warning that by the time the system is deployed, America’s adversaries “may already have a capability out there that negates whatever advantage the U.S. was trying to achieve.” And when adversaries build more, proponents of such weapons “will say we have another deterrence gap.”

Because any nuclear weapon deployed on submarines has unavoidable strategic undertones, experts in the Caution Model also worry that allies and adversaries may perceive SLCM-N less as a theater-level option and more as a strategic delivery system, increasing fears of surprise attack or even a disarming first strike.

Finally, these experts question whether SLCM-N adds meaningful capability relative to its costs. They point to existing and planned alternatives, including the W76-2 warhead on SLBMs, air-launched cruise missiles, and the LRSO (long-range standoff weapons), and argue that any deterrent benefit from SLCM-N would likely be temporary as adversaries adapt. They also emphasize opportunity costs: SLCM-N could divert resources from already-strained modernization programs, impose operational burdens on the Navy, displace conventional weapons on attack submarines, and offer limited signaling value—even for allies—precisely because submarines are designed to remain unseen. As one expert put it bluntly, “I don’t think this is decisive for Japan or South Korea.”

Taken together, this model emphasizes restraint, predictability, and transparency as the foundations of stability. It assumes that escalation is more likely to arise from accidents, misperceptions, or system failures than it is from deliberate aggression. Accordingly, it privileges diplomacy, risk-reduction mechanisms, and clear communication as instruments of maintaining equilibrium. Ambiguity is viewed not as strategic leverage but as a source of danger—an invitation to the adversary to probe further.

Across these arguments, experts aligned with the Caution Model expressed lower confidence in their assessments than their Confidence Model counterparts. They treated uncertainty as difficult to manage and warned against assuming that additional hardware can compensate for political will.

Beneath the Arguments: Decision Styles Within Confidence and Caution

Taken together, the Confidence and Caution Models capture two dominant decision styles that experts use to think about deterrence, escalation, and uncertainty. (The Contingent Model, discussed below, reflects a shared approach rather than a shared style.) The Confidence Model centers on emboldening—showing strength to prevent adversary opportunism born of perceived weakness. This decision style treats risk as something to be managed through action rather than eliminated through control. It seeks gains in deterrence credibility and strategic advantage through decisiveness, embracing risk as a tool for shaping adversary behavior amid uncertainty.

The Caution Model, by contrast, focuses on preventing accidents, misperceptions, and inadvertent escalation arising from ambiguity. Its decision style is prevention-focused and highly sensitive to uncertainty, which it seeks to reduce through clarity, guardrails, and institutional constraints. Escalation is assumed to stem primarily from human or systemic errors—misunderstandings, misinterpretations, or miscommunications—and stability is pursued by minimizing noise and maximizing predictability. In this style, stability and confidence depend on mechanisms that constrain uncertainty and make adversary behavior more legible, such as arms-control agreements, crisis hotlines, and verification regimes. The resulting decision seeks loss avoidance through control and clarity: Risk is managed not by embracing uncertainty but by designing systems and behaviors that make it legible and containable.

Figure 3 summarizes how these two decision styles map onto the core arguments and risk preferences that experts most frequently invoked when discussing SLCM-N.

Experts aligned with the Confidence Model argue that the United States faces a significant deterrence gap vis-à-vis adversaries—and a parallel assurance gap vis-à-vis allies—and that SLCM-N helps address both. Many in this group treat SLCM-N as a nonstrategic capability precisely because it enables more proportional and flexible response options below the level of large-scale strategic exchange. Strategic ambiguity is therefore viewed as a benefit rather than a flaw: Adversaries should contemplate how, not whether, the United States would respond to a potential aggression. As one expert argued, “If you don’t provide an aggressor with probability that we have local capabilities…then deterrence is undercut.” Another expert shared this view, noting that SLCM-N not only maintains but improves the United States’ deliberate ambiguity, and “maintaining that ambiguity in our doctrine, in our policy, is very, very important.” Another framed the problem diagnostically, noting that Russia and China present “two very different deterrence gaps”—Russia poses an immediate risk, while China represents a longer-term challenge.

Experts aligned with the Caution Model take the opposite view. They argue that increasing nuclear risk—regardless of the lever that triggers it—is unacceptable and that the United States does not face a deterrence gap with Russia and China. From this perspective, SLCM-N adds at best marginal value to an already sufficient force posture. Skepticism about expanding nuclear options is central to this logic. As one expert put it bluntly, “How many options does the president need?” These experts favor transparency and restraint over ambiguity, warning that escalation risks cannot be reliably managed through signaling or force design alone, and call for “more clarity, not less clarity, about our nuclear posture.”

Interestingly, disagreement over SLCM-N does not map cleanly onto whether experts view nuclear weapons as “strategic” or “nonstrategic.” Several experts across models rejected the distinction altogether. One Confidence Model expert argued that “in this era, any nuclear weapon is of strategic importance,” yet still supported SLCM-N as a useful capability. By contrast, Caution Model experts often drew the same conclusion—that any nuclear use would be “effectively strategic”—but used it to argue against adding nuclear options. As one Caution Model expert noted, “Nuclear things that come out of submarines are very strategic and very much intended to have a deterrent effect, and so that really worries me.”

This divergence highlights that the core disagreement is not about terminology but about whether recognizing the strategic nature of nuclear use implies restraint through fewer options or stability through more options.

Figure 4 complements this analysis with a descriptive word-frequency comparison of interview transcripts, illustrating how experts aligned with each mental model tended to talk about SLCM-N. We identified recurring terms across interviews and then counted uses by each expert. Experts were classified under the Confidence or Caution Model based on our prior analysis of their overall reasoning and position in the opinion space illustrated in Figure 1 (not based on word usage). Term frequencies were then aggregated within each model and visualized to highlight patterns of emphasis.

These word clouds should be read as reflecting differences in framing and emphasis, not exclusive ownership of particular terms. Experts in both models discussed escalation, risk, stability, and credibility, often in starkly different ways. What distinguishes the two models is how frequently and centrally these concepts featured in their reasoning.

These figures are not intended to suggest that all experts fall neatly into one of two camps. As shown in the opinion-space mapping and clustering analysis (see Figures 1 and 2), a third group occupies an intermediate position, drawing on both confidence- and caution-oriented assumptions. The Contingent Model discussed below reflects this conditional mode of reasoning, which does not constitute a third pole so much as a flexible position between the two dominant models.

The Contingent Model: Pragmatic and Limited Endorsement

Experts aligned with the Contingent Model do not agree on a single judgment about SLCM-N’s net effect on deterrence or strategic stability. Instead, they are united by how they evaluate the system: through conditional, context-specific reasoning rather than categorical claims. Experts in this group tended to draw on elements of both the Confidence and Caution perspectives; rely on conditional reasoning; and express low to moderate levels of epistemic confidence, having more of an information-seeking mindset and drawing multiple conclusions.

Across interviews, these experts repeatedly emphasized that SLCM-N’s effects cannot be assessed in isolation but depend on assumptions about timing, concepts of operation, signaling, adversary interpretation, and the broader strategic environment. As one expert noted, “Any new capability always faces the challenge of ‘It’s not here yet, so we don’t know how we intend to use it,’” underscoring the difficulty of evaluating a system whose employment concepts and political context remain unsettled. Whether SLCM-N is useful in a particular conflict is, per one expert, “going to be up to one person [the president] and…highly context-dependent.”

From this perspective, SLCM-N is neither inherently stabilizing nor inherently destabilizing. Its impact varies across phases of conflict and modes of employment. One interviewee maintained, “SLCM-N is not a game-changer to my mind.” As a result, experts in this group consistently rejected generalized or categorical arguments about deterrence “gaps” or escalation dynamics, instead asking how the system would function under specific conditions. As one expert put it, the relevant question is not whether SLCM-N is good or bad but “what problem is it actually trying to solve.” Another cautioned against overweighting any single capability, arguing that “we are well beyond a world in which the deployment of one nuclear-capable system has a fundamental change in the stability and instability dynamics of the present or the near future.”

A distinguishing feature of the Contingent Model is differentiation among phases of a conflict. Many experts explicitly distinguished peacetime, crisis, and wartime effects. In peacetime, SLCM-N was often viewed as neutral or modestly positive, with potential value primarily in allied assurance. In crisis scenarios, however, these experts identified both the greatest potential utility and the greatest risk: generation or deployment of SLCM-N could signal resolve and complicate adversary planning, but it could also accelerate escalation if signaling is misinterpreted. One expert summarized this tension succinctly, noting, “The study of nuclear deterrence most challengingly is the study of the inside of the head of an adversary decision maker. That’s a difficult space to access.” In wartime, SLCM-N was discussed less as a deterrent than as a possible tool for managing escalation and shaping the scope of subsequent phases of conflict.

Rather than focusing on the weapon’s technical attributes alone, experts in this group emphasized concepts of operation and employment choices as the primary determinants of risk and value. These include variables such as storage choices, fielding numbers, and commingling choices. Many of the risks referred to by the Caution Model, such as misperception and entanglement, were therefore seen as contingent on operational and political decisions rather than intrinsic features of the capability itself. As one expert explained, “It’s not just about nuclear versus conventional; it’s about where it’s being used, how it’s being used, and how the adversary assesses its own security.”

This model is marked by intragroup heterogeneity on certain issues. Variation within the Contingent Model is especially noticeable on questions of visibility versus ambiguity. Some experts argued that visible generation and clearer signaling (as with the air leg) can be stabilizing in crises as they can demonstrate resolve. Others saw ambiguity surrounding SLCM-N’s presence as potentially complicating adversary decision-making and increasing caution. Importantly, these differences were framed not as definitive conclusions but as context-dependent hypotheses. One expert stressed that ambiguity should not be treated as unique to SLCM-N, arguing that “I wouldn’t differentiate the strategic ambiguity of this system from our broader approach to all things nuclear,” while another emphasized that transparency about purpose and posture remains essential for allied confidence specifically.

Experts in the Contingent Model also expressed a pronounced tendency toward information-seeking and epistemic humility. They frequently highlighted uncertainties and were cautious about claims of control over escalation dynamics. As one interviewee noted, “I’m of two minds.” Several stressed that deterrent effects, if they exist, may be temporary as competitors adjust, and that SLCM-N’s relevance could be undercut—or amplified—by developments elsewhere, either within the U.S. force structure or in alliance or adversary politics. As one interviewee observed, “Allied assurance is like a magical, unfillable bucket.” Another added that “whatever deterrence value you squeeze out of [SLCM-N] is temporary until [adversaries] come up with a way to compete their way out of that deterred state.”

As such, the Contingent Model becomes analytically distinct from both the Confidence and Caution perspectives, understanding SLCM-N not as a decisive solution but as a contingent option whose value depends on choices yet to be made. Rather than anchoring on a dominant theory of deterrence or privileging a single risk pathway, experts in this group tend to reason through conditional logic, asking how outcomes vary across contexts, actors, and phases of interaction. Their judgments are shaped less by first principles or doctrinal commitments than by situational assessment and comparative reasoning.

Decision-making within this model emphasizes problem framing over solution advocacy. Experts tend to begin by interrogating what specific strategic or political problem a capability is intended to address, and only then do they assess whether SLCM-N meaningfully contributes under those conditions. This results in a tendency toward incremental evaluation, where capabilities are assessed as part of a broader portfolio rather than as decisive instruments in their own right.

The Contingent Model also reflects an uncertainty-acceptant decision style, and experts in this group frequently acknowledge the limits of prediction. Rather than resolving uncertainty through confident judgment (as in the Confidence Model) or treating it as a source of risk requiring constraint (as in the Caution Model), they treat uncertainty as an enduring feature of the strategic environment that must be continuously managed.

In practical terms, this decision style favors effective uncertainty management through option preservation, adaptive planning, and ongoing reassessment over early commitment or categorical judgments. It is analytically well-suited to environments characterized by deep uncertainty, but it also resists clear bottom-line conclusions, which helps explain why this group does not converge on a single verdict about SLCM-N’s net effect.

Figure 5 below lists key context-dependent factors that experts in the Contingent Model often refer to throughout their interviews.

How Confidence and Counterfactual Reasoning Shape Nuclear Risk Assessments

The key dimensions differentiating experts’ views on SLCM-N include not only the conclusions they reach but also the degree of confidence with which they reach them and how they engage uncertainty through counterfactual reasoning. To examine confidence, we asked how certain experts felt in their judgments about SLCM-N relative to other nuclear policy questions. Additionally, to observe how experts handled uncertainty, we asked them to envision plausible futures in which SLCM-N produced effects opposite to those they anticipated—an exercise designed to probe whether uncertainty was treated as something to be resolved or as something to be explored and incorporated into their assessments. Higher self-reported confidence was typically associated with constrained uncertainty—treating key assumptions about SLCM-N as relatively fixed—whereas lower or more qualified confidence reflected greater openness to alternative futures.

Experts aligned with the Confidence Model often grounded their certainty in long experience in the field. As one expert stated, “I’m equally confident in all of [my views] because I’ve been in the business for a long time. I am very firm in my views.” Another attributed confidence to institutional trust, noting that “my high confidence is because I have innate trust…[and] an unspoken assumption in the fact that [the United States] as a democracy behaves responsibly.” The same expert contrasted this with “zero trust…with the Russians and the Chinese” based on long experience engaging with them on nuclear and arms control issues.

Many experts aligned with the Confidence Model argued that under current and anticipated threat conditions vis-à-vis Russia and China, SLCM-N functions as a stabilizing counterweight. Within this framing, the risks of not deploying SLCM-N were consistently judged to outweigh the risks of deployment. This logic extended to cost considerations as well; one expert argued that SLCM-N is “absolutely worth the price, even at [$]30 billion.” Counterfactual scenarios in which SLCM-N became destabilizing were generally described as either highly unlikely or contingent on profound structural shifts in the international system that experts viewed as implausible. As one interviewee put it, only in a world where “catastrophic peace [has] broken out…[and] everything’s fine” would SLCM-N have little or no strategic effect—an intentionally ironic way of underscoring how unlikely they view that scenario.

By contrast, we observed that experts aligned with the Caution and Contingent Models exhibited a markedly different relationship with uncertainty, treating it as an inherent component of their logic. Several explicitly flagged uncertainty in their judgments, using phrases such as “I genuinely don’t know” or “I’m not very confident.” Notably, in this model, the expressions of uncertainty were often paired with the same deep professional experience that we found in the Confidence Model. “I’ve stared at this problem a lot, so I feel pretty comfortable in how I think about it,” one expert noted. This highlights a central distinction between the models: While both draw on experience, Confidence Model experts tend to use it to justify firmer conclusions, whereas Caution and Contingent Model experts invoke experience to emphasize epistemic humility and openness to revision.

Taken together, these differences suggest that disagreement over SLCM-N reflects not only substantive judgments about deterrence and escalation but also deeper differences in how experts reason amid uncertainty—how firmly they anchor their conclusions, how seriously they engage counterfactuals, and how willing they are to revise beliefs as future conditions unfold.

Areas of Agreement Across Expert Views

Across interviews, several areas of agreement emerged regarding both SLCM-N’s potential role and its limits. Most notably, experts broadly agreed that SLCM-N is not a “magic bullet” for deterrence. While many acknowledged that the system could strengthen U.S. deterrence posture under certain conditions, few viewed it as a decisive or standalone solution to perceived credibility gaps. Instead, deterrence effectiveness was widely seen as hinging on communication, signaling, and broader force posture rather than arsenal size alone—a noteworthy point given that the number of SLCM-Ns to be deployed remains classified.

Second, experts across different mental models generally agreed that SLCM-N could play an effective role in signaling U.S. commitment to allies, particularly in the Indo-Pacific, where partners such as South Korea and Japan increasingly question the credibility of U.S. extended deterrence. At the same time, most emphasized that SLCM-N would be only one component of alliance assurance, insufficient on its own to resolve underlying political or strategic concerns.

Third, there was broad agreement that SLCM-N would be more effective in the Indo-Pacific than in Europe, reflecting the region’s maritime geography, the lack of forward-deployed U.S. nuclear options, and distinct threat perceptions. By contrast, many experts viewed the system as offering more limited benefits in Europe, where existing dual-capable aircraft already provide a visible manifestation of extended deterrence.

If expert judgments are shaped by underlying mental models rather than facts about the system, an important question is whether structured engagement with alternative futures can meaningfully alter how experts think about the system. Phase II of the project used scenario planning to test how those assumptions operate under stress. In practice, scenario planning does not dissolve mental models; it surfaces them.² By placing participants in systematically different futures, the exercise forces them to apply their assumptions under conditions that disrupt present-day defaults.³ This does not eliminate underlying biases, but it does temper them by diminishing anchoring effects, challenging preferred trajectories, and revealing how each mental model responds when key variables shift.⁴ The result is not a harmonized view but a clearer understanding of why experts diverge and how their divergences depend on contingent features of the future.

To move from present-day judgments to forward-looking assessment, we conducted a structured scenario-planning exercise grounded in insights from Phase I. Building on what experts believed—and why their beliefs differed—we examined how competing assumptions about deterrence, escalation, and signaling would shape judgments across plausible future strategic environments in which SLCM-N might operate.

The exercise began with a horizon-scanning process, identifying a broad set of political, technological, and military factors that could shape SLCM-N’s future relevance. Participants then assessed these factors using two criteria: uncertainty about their future values and their potential impact on the value and risks of SLCM-N. Through facilitated discussion and clustering, we narrowed this list, eliminated overlapping variables, and focused on those that most consistently structured disagreement in Phase I rather than those that simply reflected present-day debates.

Two drivers emerged as both highly uncertain and highly consequential because they operate as system-level modifiers rather than marginal inputs. The first is the pace of technological change: whether advances in sensing, tracking, and strike capabilities unfold at a steady pace or through disruptive breakthroughs. This variable matters not only for technical performance but also because it shapes assumptions about survivability, escalation control, and the durability of existing deterrence relationships. Small changes in its trajectory can therefore produce nonlinear effects on perceived stability.

The second driver is how U.S. nuclear posture is perceived by allies and adversaries—specifically, whether U.S. nuclear forces, including SLCM-N, are interpreted as primarily defensive and stabilizing or as increasingly offensive and threatening. This variable is critical because deterrence hinges on interpretation rather than capability alone: The same system can reassure allies or provoke adversaries depending on how intent is inferred. As a result, perceptions of U.S. posture directly mediate whether SLCM-N functions as a stabilizing signal or a source of escalation risk.

Together, these variables capture key aspects of both the material and interpretive dimensions of deterrence and help explain why similar capabilities can generate sharply different risk profiles across plausible futures.

Using these two drivers, we constructed a two-by-two matrix that generates four distinct futures for SLCM-N (Figure 6). Each quadrant represents a different combination of technological change (steady versus disruptive) and perception of U.S. nuclear forces (defensive versus offensive).

Participants were then assigned to one future and asked to assess how SLCM-N functions within that environment: how it shapes allied and adversary perceptions, affects escalation dynamics, and operates across peacetime, crisis, and conflict. The sections that follow examine each future in turn, identifying the conditions under which SLCM-N is stabilizing, destabilizing, or largely neutral.

Future 1: Managed Deterrence

Tech Pace: Steady
U.S. Posture: Viewed as defensive
SLCM-N’s Role: Neutral baseline, selective hedge, limited distinct value

In this future, steady technological change converges with a widespread belief that the United States maintains a fundamentally defensive nuclear posture. Steady advances in sensing, anti-submarine warfare, missile defense, and autonomy improve performance at the margins but do not fundamentally undermine the survivability of existing forces. Command-and-control systems and delivery platforms evolve slowly due to complexity and institutional constraints. U.S. nuclear modernization is interpreted as planned and evolutionary rather than transformative, reinforcing perceptions of a primarily defensive posture.

Steady technological change still creates pressure but not disruption. Improvements in Chinese undersea sensing modestly increase risks to U.S. submarines, prompting incremental responses: investments in survivability and resilience rather than wholesale changes to force structure. Missile-defense developments follow similar trajectories: Allies largely see them as reassurance tools, while adversaries view them as manageable adjustments. Taken together, these trends do not materially destabilize the strategic environment.

Within that context, participants judged SLCM-N to have limited distinct value. Because both the technological environment and perceptions of U.S. intent remain relatively predictable, SLCM-N is seen as largely redundant with existing capabilities and unlikely to reshape escalation dynamics or change how adversaries interpret U.S. intentions. Its relevance is therefore narrow: a selective hedge for specific regional contingencies where other options carry clear operational or signaling liabilities. Participants emphasized, for example, that B61 gravity bombs are not forward-deployed in Asia; air-launched cruise missiles have long flight times; and low-yield submarine-launched ballistic missiles (SLBMs) can be misread because any SLBM launch might be interpreted as strategic. Against this backdrop, SLCM-N can offer a lower-visibility option in the limited set of scenarios in which timeliness, survivability, and escalation management matter more than raw capability. Even then, its value lies in preserving options, not in shifting the broader balance.

Expectations remain modest: Participants emphasized that leaders tend to think in categorical terms (nuclear versus non-nuclear), which limits how much an additional “tailored” option can influence real crisis behavior. As a result, SLCM-N may marginally expand a menu of politically viable responses, but it does not become a decisive tool for shaping escalation.

To assess how these dynamics vary across stages of state interaction, participants evaluated SLCM-N’s effects in peacetime, crisis, and conflict. In peacetime, SLCM-N provides marginal reassurance and niche deterrence value with low misinterpretation risk because adversary paranoia is limited and U.S. intent is relatively trusted. In crisis, it offers some additional flexibility for signaling and messaging, but participants generally agreed it would not significantly alter crisis dynamics. Allies tended to view it as a useful hedge, while adversaries assigned it only modest deterrent weight in a context where technological trajectories are steady and perceptions of U.S. posture remain defensive. In conflict, SLCM-N is unlikely to drive escalation dynamics, with effects overshadowed by larger nuclear systems; even under heightened stress, adversary fears of U.S. first use remain limited in this future precisely because the baseline expectation is restraint rather than opportunism.

Overall, Managed Deterrence is a future where steady technological change and trusted defensive U.S. intent keep deterrence architecture stable. In that setting, SLCM-N stays in the background: a neutral baseline capability and a selective hedge for narrow contingencies, not a central driver of strategic competition or stability.

Future 2: Assertive Stability

Tech Pace: Steady
U.S. Posture: Viewed as offensive
SLCM-N’s Role: Conditionally stabilizing—with limits

In this future, steady technological change converges with a persistent belief that the United States is pursuing a more assertive, offensive nuclear posture. Even routine modernization is viewed as part of a counterforce-oriented strategy: Force structure adjustments, visible deployments, and public messaging are read as signals that Washington aims to shape regional environments and may be willing to act preemptively in a severe crisis. Allies generally welcome strong U.S. commitment but are also uneasy about cues that suggest shorter decision timelines or more aggressive deterrence concepts.

Within that context, participants judged SLCM-N to be stabilizing only conditionally—and in ways that varied across phases of state interaction. In peacetime and early in crises, the system was seen as strengthening U.S. reassurance and signaling, contributing to deterrence without materially altering the strategic balance. Adversaries interpreted SLCM-N through a generally skeptical lens, viewing it as part of a broader suite of U.S. regional capabilities, but steady technological change and clear U.S. presence were judged to reinforce restraint.

As tensions rise short of war, U.S. forward presence and regional commitments become more salient, and SLCM-N is seen as contributing to deterrence messaging alongside long-range strike and other flexible systems. Its stabilizing effects were judged to persist, but participants emphasized that these benefits had clear limits: SLCM-N shaped expectations and enhanced allied resilience to coercion, yet it did not decisively influence whether conflict would occur. Visibility and scale were seen as important, however, as larger or more prominent deployments increased adversary concern about U.S. counterforce options, even when adversaries doubted Washington’s ability to neutralize their arsenals.

During conflict, participants judged that the stabilizing logic would be reversed. In wartime, SLCM-N becomes one of several capabilities that heighten adversary anxiety, compress decision time, and increase the risk of inadvertent escalation. Adversaries, particularly China, are seen as fearing that the United States might use SLCM-N or related assets to preemptively degrade command and control or to blunt escalation options. Narrative effects amplify these concerns: Years of U.S. messaging framing SLCM-N as a response to regional challenges could, in wartime, reinforce perceptions that it is optimized for rapid, limited counterforce use. Missile defense further complicates interpretation, as even modest improvements activated worst-case thinking and could prompt adversaries to accelerate arsenal expansion or escalate earlier than intended.

Overall, in this future, SLCM-N is stabilizing only up to a point: It strengthens deterrence messaging and alliance confidence before a conflict, but once fighting begins, its association with a broader counterforce-oriented posture amplifies adversary anxiety and escalation risk. The conditional stability of this future stems not from the weapon itself but from how SLCM-N is interpreted within an already skeptical strategic framing of U.S. intent.

These mixed effects stem from the broader strategic frame: steady technological evolution combined with persistently negative perceptions of U.S. intent. Because adversaries already view the U.S. posture as offensive, they read SLCM-N as part of a wider architecture built for early advantage, not as a discrete deterrent tool. This interaction between perception and capability is what produces the conditional stability of Future 2.

Future 3: Adaptive Deterrence

Tech Pace: Disruptive
U.S. Posture: Viewed as defensive
SLCM-N’s Role: Stabilizing under narrow conditions/conditionally stabilizing with limits

In this future, rapid and disruptive technological change converges with a widespread belief that the United States maintains a fundamentally defensive nuclear posture. Advances in autonomy, decision support, sensing, counterforce capabilities, integrated air and missile defense, and new delivery systems (including long-range strike) produce a continually shifting landscape. These developments compress operational timelines, obscure the survivability of long-standing force structures, and create persistent uncertainty for both allies and adversaries. While the perception of a defensive U.S. posture is perhaps not intuitive in this environment, the belief emerges as a product of how U.S. declaratory policy, alliance reassurance practices, and visible investments in command-and-control resilience continue to signal restraint even as capabilities evolve. Despite technological disruption, the United States is widely perceived as maintaining a defensive, deterrence-oriented nuclear posture (centered on restraint, assurance, distributed command and control, and continuity of extended deterrence commitments).

Within the working group’s interpretation of this environment, SLCM-N is treated as a central stabilizing feature of the deterrence architecture. Their view is that rapid technological disruption does not reduce SLCM-N’s utility or introduce vulnerabilities distinct from those faced by other nuclear systems. Even in scenarios of increased “ocean transparency,” in which advances in sensing technologies make submarines easier to detect, or in futures marked by new anti-submarine capabilities, fractional orbital bombardment systems, or more layered missile defenses, SLCM-N is described as no more vulnerable than other legs of the force and as adaptable to technological evolution over time.

From this perspective, SLCM-N’s value lies in its prompt availability, flexibility, and independence from host-nation support or overflight permissions. Participants emphasized its ability to put an expanded, evolving target set at risk as adversaries modernize and to preserve ambiguity in U.S. decision-making under conditions of rapid change. In a highly dynamic environment, SLCM-N was treated as strengthening both central and extended deterrence, particularly for allies such as Japan, South Korea, and Poland, who were assumed to seek visible and credible indicators of U.S. resolve amid technological disruption.

Participants further argued that adversary advancements—expanding arsenals, new delivery systems, and destabilizing technologies—would otherwise erode the credibility of existing U.S. options. In this context, SLCM-N, integrated with broader modernization efforts such as Columbia-class nuclear-powered ballistic missile submarines (SSBNs), long-range standoff weapons (LRSO), and the B-21 bomber, can slow or reverse erosion of the current posture. This group also discussed potential evolution of SLCM-N, including hypersonic variants, variable-yield or insertable-core warheads, and possible deployment from additional platforms such as surface combatants or even road-mobile systems. In their view, such adaptations would ensure continued relevance as technological conditions evolve and would preserve ambiguity and flexibility for national decision makers.

The scenario design originally asked whether SLCM-N would be stabilizing, neutral, or destabilizing under conditions of rapid technological disruption and a U.S. deterrent posture. Interestingly, the group moved quickly to a conclusion that it would be stabilizing across peacetime, crisis, and conflict. They did not engage deeply with how alternative assumptions might shift that outcome, nor did they explore how allied or adversary perceptions could diverge from U.S. intent. They focused instead on how SLCM-N could be integrated into a broader vision of posture adaptation and resilience in a disruptive technological era.

As a result, the working group’s version of Future 3 reflects a strong presumption that technological disruption itself increases the value of SLCM-N. In this interpretation, rapid change is understood to erode confidence in the credibility, usability, and proportionality of existing nuclear response options, creating new deterrence gaps and signaling risks. Under conditions of compressed timelines and heightened ambiguity, SLCM-N is framed as a means of restoring interpretive clarity, offering a flexible and visibly distinct capability that reassures allies, mitigates perceived response shortfalls, and reinforces extended deterrence as technological change accelerates.

However, the original scenario design could have allowed for a different baseline assumption about how stability is produced. In that alternative framing, technological disruption would not automatically generate instability requiring new nuclear capabilities. Instead, stability arises from the interaction between disruptive technologies and a U.S. posture that is clearly defensive—one emphasizing reassurance, transparency, diversified planning, and continuity of commitments. Within this logic, SLCM-N functions as a flexible hedge rather than a primary stabilizer: a supporting capability that complements a stability-producing posture rather than the principal source of stability.

The working group’s discussion diverged from this logic by elevating SLCM-N to a central pillar of deterrence, advocating expansion across multiple platforms, and assuming that ambiguity and capability growth would be interpreted as stabilizing.

Taken together, these interpretations illustrate that Future 3 contains a wide range of plausible outcomes. Depending on how technological change interacts with perceptions of U.S. intent, SLCM-N could remain a limited adaptive tool, become a more assertive posture element, or land somewhere between these positions.

In peacetime, high transparency and rapid technological change increase uncertainty across the strategic environment, but assessments diverge on whether this uncertainty is stabilizing or destabilizing. Within the working group’s interpretation, visibility into U.S. capabilities, including SLCM-N, reinforces perceptions of restraint and defensive intent, particularly when coupled with alliance consultation and consistent signaling. From this perspective, SLCM-N functions as an assurance mechanism that mitigates perceived deterrence gaps and reduces incentives for adversaries to probe U.S. commitments.

Under the alternative baseline, however, the same transparency interacts with technological disruption to heighten anxiety and reinforce worst-case thinking. Rather than reassuring, visibility amplifies concern about latent escalation dynamics, and SLCM-N is interpreted as evidence of coercive U.S. intent. In this framing, arms racing, force dispersal, and hedging behavior accelerate even in the absence of an acute crisis.

During crises, these differences become more pronounced. The working group views SLCM-N as strengthening deterrence by expanding credible response options without requiring early or escalatory employment. Its mobility and survivability are assumed to complicate adversary calculations and discourage opportunistic escalation, while reassuring allies of U.S. resolve and commitment. In this interpretation, SLCM-N contributes to clearer signaling by reducing pressure for rapid escalation.

By contrast, the alternative baseline assumes hypervigilant adversaries operating under compressed timelines, for whom SLCM-N movements are interpreted as preparation for early nuclear use. Allies respond unevenly: Some experience reassurance, while others express heightened fears of entrapment or inadvertent escalation. As competitive adaptation accelerates, signaling becomes increasingly ambiguous, undermining efforts to communicate either restraint or resolve.

In conflict, the working group anticipates that SLCM-N contributes to escalation management rather than escalation pressure. Integrated with broader modernization efforts, it is seen as preserving ambiguity for U.S. decision makers while sustaining deterrence credibility and alliance cohesion under stress.

The alternative baseline, however, suggests that the cumulative effects of mistrust, compressed decision timelines, and ambiguous signaling erode escalation control. In this case, SLCM-N’s presence does not stabilize behavior but instead narrows the space for calibrated nuclear decision-making, increasing the risk of rapid and uncontrolled escalation.

Taken together, assessments of SLCM-N in Future 3 highlight its fundamentally contingent effects on strategic stability. Under the working group’s interpretation, SLCM-N functions as a stabilizing capability that enhances assurance, expands credible response options, and supports escalation management in an environment of rapid technological change. Under the alternative baseline, however, SLCM-N’s effects are not intrinsic to the system itself. Its stabilizing potential depends on the surrounding posture, the quality of signaling and consultation, and how technological disruption shapes interpretation rather than capability alone. In this future, SLCM-N remains conditionally stabilizing, valuable as a hedge under narrow circumstances but insufficient as a primary source of stability in an environment defined by rapid technological change.

Crucially, the effects of SLCM-N in this future are shaped less by any single factor than by the interaction among technological disruption, signaling practices, and institutional cognition under stress. Rapid innovation amplifies the volume and speed of signals while simultaneously degrading shared interpretive frameworks, increasing the risk that actions intended as reassurance are read as preparation or coercion. Transparency, alliance consultation, and posture continuity can mitigate these dynamics, but only imperfectly and unevenly across actors. Where interpretive capacity is strong, SLCM-N can function as a bounded hedge within a clearly defensive posture. Where it is weak, the same capability interacts with compressed timelines and worst-case reasoning to magnify anxiety and competitive adaptation. In this sense, SLCM-N’s stabilizing or destabilizing effects emerge from second-order interactions among technology, perception, and decision-making processes rather than from the presence of the capability itself.

Future 4: Technological Coercion

Tech Pace: Disruptive
U.S. Posture: Offensive
SLCM-N’s Role: Tilts towards destabilizing

In this future, rapid technological change converges with a widespread belief that the United States has an offensive nuclear posture. Breakthroughs in AI-enabled sensing, autonomous maritime systems, hypersonic delivery platforms, and integrated missile defenses, including a fully operational Golden Dome missile defense system, convince adversaries that Washington seeks early warfighting options and has growing confidence in its ability to blunt or absorb retaliation. Military movements are highly visible, attribution is fast, and states operate with continuous transparency and hypervigilance. Adversaries interpret nearly every new U.S. capability as aggressive, hardening their threat perceptions and reducing their risk tolerance.

Adversaries respond by expanding and diversifying arsenals and by experimenting with more reactive postures. Russia and China increase both strategic and nonstrategic nuclear forces and invest in systems that complicate U.S. operations and defenses. China increasingly embraces low-yield options, develops a wider range of warhead types, adopts “put a nuclear option on everything” thinking, and seeks asymmetric advantages in space and counterspace. Under pressure, Chinese planners consider greater automation in nuclear decision-making and more rapid launch postures. Russia, constrained conventionally, leans on cyber-operations, gray-zone activities against allies, and disruptive behavior in regions such as the Middle East and the Korean Peninsula. Both states explore space-based nuclear or anti-satellite systems and other “exotic” capabilities that challenge U.S. sensing and missile defense architectures.

Allies become more capable and operationally autonomous. In Europe, long-standing investments in conventional forces reduce day-to-day reliance on U.S. power even as NATO’s strategic alignment endures. In both Europe and Asia, however, leaders worry about entrapment in crises shaped by a U.S. posture that appears increasingly aggressive. Some allies view new American capabilities, including SLCM-N, as overdue demonstrations of resolve. Others see them as evidence that Washington has shifted away from a primarily defensive role and now accepts higher escalation risks, particularly under the perceived protection of advanced defenses and strike systems.

Within this setting, SLCM-N fits neatly into a broader pattern of new and modernized U.S. capabilities that adversaries read collectively as coercive. Its deployment at sea, with invisibility and unknown employment concepts, reinforces their belief that the United States wants flexible options early in a conflict and is willing to shorten decision times by operating close to their territory. This perception amplifies paranoia, accelerates efforts to disperse and harden forces, and strengthens arguments for launch-under-attack or even launch-on-warning postures. The discrimination challenge, especially amid eroding trust in sensors and data, raises the risk that any movement or signaling involving SLCM-N will be interpreted as preparation for first use.

For allies, SLCM-N’s effects tilt toward destabilization rather than reassurance. In peacetime, some see it as a needed adjustment that closes perceived gaps relative to expanding Chinese and Russian dual-capable systems and signals U.S. readiness to respond across escalation levels. But others view it as another indicator that U.S. nuclear policy has become less predictable and that Washington may rely on nuclear tools more readily under the Golden Dome’s perceived protection. In crisis conditions, these divergent interpretations complicate alliance management and undermine coherent signaling. While SLCM-N may reassure some actors and deter certain forms of aggression, in an environment shaped by technological coercion, its marginal effect is to amplify existing anxieties about U.S. offensive intent and accelerate competitive nuclear and technological adaptation.⁵

In a variant of Future 4 suggested by some group members, rapid technological disruption still reshapes the strategic environment, but U.S. nuclear posture is interpreted by many actors as restrained and rule-bound rather than coercive. This pathway rests on the assumption that shared interpretive frameworks remain sufficiently robust that signaling, declaratory policy, and alliance consultation continue to anchor assessments of intent even as capabilities evolve. Although new capabilities increase baseline uncertainty, they do not consistently trigger worst-case threat perceptions because U.S. signaling, declaratory policy, and alliance consultation anchor expectations of defensive intent. In this pathway, SLCM-N adds options to the U.S. deterrence toolkit but remains secondary to the broader posture shaping perceptions of intent. Allies are generally supportive, interpreting the system as consistent with established commitments, and adversaries tolerate its presence as one element within a highly competitive but familiar technological environment. This reading diverges from the dominant Future 4 logic by assuming that transparency and signaling can still encourage benign interpretations of U.S. intent.

During crises in this alternative Future 4, emerging technologies generate noise and ambiguity, compressing timelines and increasing cognitive strain, but U.S. intent is not widely assumed to be escalatory. Misinterpretation risks thus stem primarily from technical complexity, sensor saturation, and information overload rather than from fears of deliberate early nuclear use. SLCM-N can in some cases clarify U.S. commitment—particularly in Asia—by reinforcing extended deterrence at moments of stress. This stands in contrast to the dominant Future 4 variant, in which the same signals are read as coercive and heighten fears of preemption or entrapment.

During a conflict in this alternative, assessments of SLCM-N’s effects hinge on U.S. employment concepts and signaling discipline. If SLCM-N is embedded within a clearly articulated escalation management framework, it may contribute to stabilizing outcomes by preserving decision space and offering options short of large-scale escalation. However, this pathway remains fragile. Even modest shifts in perception—toward viewing U.S. capabilities as enabling warfighting rather than deterrence—would quickly collapse this stabilizing logic and pull dynamics back toward the dominant Future 4 pattern of technological coercion.

In this alternative Future 4, outcomes are driven by the effects of interaction among technological acceleration, signaling discipline, and persistent shared interpretive frameworks. Rapid innovation increases uncertainty and compresses decision timelines, but its destabilizing potential is mediated by how signals are processed rather than by capability growth alone. Where transparency, alliance consultation, and declaratory consistency reinforce expectations of restraint, new capabilities are incorporated into existing mental models instead of triggering worst-case escalation dynamics. SLCM-N’s effects therefore depend on its interaction with these interpretive and institutional buffers: When embedded within a posture that reliably communicates defensive intent, it functions as an additional option within that posture; when those buffers weaken, the same capability risks tipping perceptions toward coercion. Stability in this variant is thus an emergent property of these interactions, not a direct consequence of technological restraint or capability limitation.

Futures Assessment

Encompassing the spectrum of uncertainty about how technology and perceptions will interact to shape strategic stability, these four futures show that SLCM-N’s effects are not intrinsic to the system but contingent on broader structural conditions. When the pace of technological change is stable and U.S. posture is perceived as defensive, SLCM-N exerts limited influence. When perceptions shift towards offensive or technological change is disruptive, it becomes an accelerant of misperception and competitive adaptation. The alternative futures demonstrate the wide range of plausible environments in which policymakers may evaluate SLCM-N’s risks, signaling value, and potential contribution to regional deterrence a decade from now.

SLCM-N’s Marginal Versus Decisive Value

SLCM-N’s influence varies widely across the four futures. It is most decisive in Future 2 (Assertive Stability), in which steady technological evolution and adversary perceptions of an assertive U.S. posture elevate the importance of visible regional capabilities. In this environment, SLCM-N becomes a meaningful instrument for shaping expectations about U.S. presence and commitment, particularly in the Indo-Pacific. It reinforces extended deterrence, strengthens early-crisis resolve, and signals that Washington intends to remain engaged even as escalation risks rise. These effects give SLCM-N disproportionate leverage relative to its size within the broader force posture.

In Future 1 (Managed Deterrence), by contrast, SLCM-N is marginal. Sustained positive perceptions of the U.S. posture and predictable technological change lower the demand for additional flexible nuclear options. Assurance is already strong, adversary paranoia is muted, and crisis stability is robust. In this setting, SLCM-N functions as a supplemental hedge or niche deterrent rather than as a capability that alters strategic dynamics. It is likewise marginal in Future 3 (Adaptive Deterrence), in which disruptive technological change introduces uncertainty but the United States is still viewed as a stabilizing actor. Although it can contribute to reassurance in specific regional contexts, its peacetime reassurance effects are overshadowed by the broader volatility introduced by rapid technological shifts and are reversed during conflicts. Its value depends heavily on signaling and employment concepts rather than on the system itself.

In Future 4 (Technological Coercion), SLCM-N is not decisive in the constructive sense, but it is highly consequential as a contributor to instability. Disruptive technological change, pervasive transparency, and negative interpretations of U.S. intent create an environment in which adversaries read SLCM-N as a coercive tool designed for early use. It becomes an accelerant of arms racing, misperception, and preemptive incentives. Although its impact on outcomes is significant, it does not decisively improve deterrence; instead, it deepens crisis instability.

Taken together, these distinctions show that SLCM-N has a positive impact or is considered useful only when perceptions of U.S. assertiveness raise the value of forward engagement but technological conditions remain stable enough to prevent runaway escalation (Future 2, Assertive Stability). In all other futures, the capability is either marginal or contributes primarily to instability rather than deterrence.

SLCM-N in the Indo-Pacific Theater

The scenario planning exercise reinforced one of our findings from Phase I of the project: that SLCM-N has the most relevance for the Indo-Pacific, though that value also varies across futures. In that region, it delivers its greatest strategic utility in Future 2 (Assertive Stability), in which technological change is steady but U.S. intentions are interpreted as more offensive, because U.S. allies in the Indo-Pacific face intense coercive pressure and place a premium on visible indicators of U.S. commitment. SLCM-N strengthens extended deterrence by demonstrating that Washington is prepared to remain engaged even as escalation risks rise, and it signals deeper U.S. interest in the region without requiring early movement of strategic forces. Adversaries, particularly China, are expected to read the capability as evidence that the United States will not be pushed out of theater, which can temper coercion at the conventional level and reinforce allied resilience in the early stages of crises.

By contrast, SLCM-N’s value is more modest in Future 1 (Managed Deterrence), when positive perceptions of U.S. intent reduce the need for additional regional signaling. Its regional utility becomes mixed in Future 4, in which disruptive technological change and negative interpretations of U.S. posture generate acute misperception risks that diminish the stabilizing benefit SLCM-N might otherwise provide. In Future 3 (Adaptive Deterrence), while rapid technological change creates uncertainty, benign interpretations of U.S. behavior keep SLCM-N’s role context-dependent rather than decisive.

Together, these comparisons show that SLCM-N’s Indo-Pacific value is highest when allies seek reassurance, adversaries test U.S. resolve, and the broader environment remains technologically manageable enough to avoid runaway escalation dynamics.

Crux Point: China’s Reaction

A crux point is a factor that plays an outsize role in determining which strategic path emerges when underlying conditions are otherwise similar. Such points matter because they show where outcomes depend most on how situations are interpreted, signaled, and acted upon rather than material capabilities alone.

Across all scenarios, discussion repeatedly returned to the question of China’s interpretation of the U.S. posture. Beijing’s reaction to SLCM-N constitutes the central crux point in this analysis, influencing whether similar technological and geopolitical pressures translate into stabilizing or destabilizing pathways.

The forecasting discussed in the next section reinforces this conclusion. Chinese nuclear expansion is the area of strongest expert consensus; China’s potential signaling behavior around Taiwan is the most uncertain geopolitical variable; and any doctrinal shifts in either would have disproportionate effects on U.S. force planning. Together, these patterns highlight that China’s response is both highly consequential and highly sensitive to interpretation.

These dynamics underscore once again that SLCM-N’s utility is not inherent to the capability itself (as scenario discussions revealed) but contingent on how Beijing interprets the deployment’s purpose, risks, and escalation thresholds. In futures where China views the U.S. posture as defensive and predictable, SLCM-N adds limited marginal value. In futures where Beijing interprets U.S. actions as competitive or coercive, SLCM-N becomes a focal point for counter-posture, signaling cycles, and crisis instability. As a result, China’s reaction consistently distinguishes stabilizing from destabilizing trajectories across all four alternatives.

In the forecasting stage, we asked experts to assign probabilities to a set of 15 questions about the strategic environment in the year 2035. Our goal was to identify indicators of drift to examine which of the four futures gain or lose plausibility in light of expert judgments about key developments, not as forecasts of inevitability or predictions of a single future.

The future scenarios developed earlier—Managed Deterrence, Assertive Stability, Adaptive Deterrence, and Technological Coercion—are treated as alternative strategic baselines against which forecasting results were interpreted. Each represents a distinct configuration of technological conditions, geopolitical behavior, and perceptions of U.S. nuclear posture.

We developed forecasting questions to capture observable developments that could signal movement toward or away from any of the four potential futures. The questions focused on changes in strategic stability conditions, posture and doctrinal adaptation, and political or behavioral shifts relevant to the scenarios. (To examine the full set of questions, refer to Figure 7.)

We then classified forecasting indicators by functional role—structural, posture/doctrinal, or political/behavioral—and weighted them according to their relevance for each scenario. We assigned weights using two criteria: (1) necessity, capturing whether a development is required for a given scenario to exist coherently, and (2) constraint power, capturing the extent to which an indicator would limit strategic choices by altering survivability, warning time, or escalation control. We applied ordinal weights using the maximum of these two criteria.

Finally, we applied expert probability assessments to the weighted indicators to evaluate patterns of reinforcement and refutation across scenarios. Rather than aggregating probabilities numerically, the analysis examines whether high-weight indicators are judged likely or unlikely and whether reinforcing indicators cluster within particular futures. This pattern-based interpretation allows the forecasting results to discriminate among the four futures, revealing which ones are being reinforced, weakened, or left contingent, and to assess how the strategic relevance of specific capabilities, including SLCM-N, varies across the four plausible futures.

Discriminating Patterns Among Scenario Futures

According to forecasting data, Managed Deterrence (tech pace steady; U.S. posture defensive) is increasingly difficult to sustain as a baseline future. Experts assign relatively low probabilities to destabilizing geopolitical shocks such as alliance withdrawal, treaty exit, explicit nuclear threats, or rapid allied proliferation (see Figure 7). But these signals are outweighed by higher probabilities of structurally disruptive developments, including expectations of significant Chinese nuclear force expansion, plausible erosion of undersea survivability, and growing confidence in missile defense effectiveness. These signals collectively undermine the structural continuity on which Managed Deterrence depends. Even in the absence of overt nuclear brinkmanship, these developments weaken the assumptions of stable mutual vulnerability and bounded competition. As a result, Managed Deterrence appears increasingly implausible as a durable trajectory toward which the strategic environment is heading. This would not be the case if technological change stalls, proves strategically inconsequential, or is distributed and absorbed across systems in ways that preserve stable mutual vulnerability, all of which would make Managed Deterrence appear to be a coherent and durable baseline future.

Assertive Stability (tech pace steady; U.S. posture offensive) remains a plausible but fragile pathway. Forecasting data show meaningful probabilities of posture and doctrinal indicators associated with competitive signaling, including Russian doctrinal revision referencing SLCM-N, nontrivial expectations of U.S. nuclear testing, and the potential deployment of SLCM-N. These developments align with a world characterized by heightened nuclear signaling and visible posture adjustment within an otherwise intact deterrence framework. Curiously, during scenario planning, members assigned to this future felt that it was the most plausible one.

However, Assertive Stability presumes that technological conditions underpinning survivability and escalation control remain largely stable. The same structural indicators that undermine Managed Deterrence also strain this assumption. As technological uncertainty increases, the signaling logic central to Assertive Stability becomes harder to sustain, rendering this world viable but increasingly contingent on technological disruption proving more limited than many experts expect. This assessment would change if technological conditions remain sufficiently stable to preserve survivability, warning, and escalation control and if competitive signaling and posture adjustments consolidate into a durable equilibrium rather than eroding under growing technological uncertainty.

Adaptive Deterrence (tech pace disruptive; U.S. posture defensive) emerges as the most strongly reinforced (or anticipated) future. Expert forecasts converge most clearly on indicators associated with technological disruption: large-scale Chinese nuclear expansion, plausible erosion of undersea survivability, and growing belief in the effectiveness of missile defense against limited strikes. At the same time, experts assign relatively low probabilities to explicit nuclear threats, alliance breakdown, or treaty exit. This combination—structural disruption without overt geopolitical rupture—is precisely the condition under which Adaptive Deterrence arises. In this world, states adapt to eroding assumptions about survivability, warning, and escalation control through greater flexibility, hedging behavior, and probing, even as institutional frameworks and formal restraint largely persist. This assessment would be altered if technological disruption either fails to materialize (or stalls) or drives overt geopolitical rupture—such as explicit nuclear coercion, alliance breakdown, or rapid abandonment of restraint—rather than adaptation within existing institutional frameworks.

Technological Coercion (tech pace disruptive; U.S. posture offensive) remains a plausible but unlikely future. While several structural prerequisites for coercive leverage appear increasingly plausible, the political and behavioral indicators required to align with this future—explicit nuclear threats, China’s abandonment of a No First Use policy, alliance or treaty collapse, or overt nuclear coercion—remain comparatively unlikely, according to expert assessments. Absent convergence across these categories, Technological Coercion does not dominate. Instead, it represents a plausible escalation pathway should multiple high-impact thresholds be crossed. This assessment would change if political and behavioral indicators converge with structural developments—most notably through explicit nuclear threats, abandonment of No First Use, alliance or treaty collapse, or sustained coercive signaling—elevating Technological Coercion from a contingent pathway to a dominant strategic trajectory.

Taken together, the forecasting results reinforce Adaptive Deterrence as the most plausible trajectory toward which our strategic landscape is headed, with Assertive Stability as a secondary but fragile alternative. Managed Deterrence is increasingly ruled out, while Technological Coercion remains a contingent risk dependent on additional geopolitical escalation.

Importantly, the two futures experts judged to be most likely, Assertive Stability and Adaptive Deterrence, sit diagonally opposite one another on the scenario matrix (Figure 6). This pattern suggests that technological change and U.S. nuclear posture are not independent variables but interact in ways that shape leaders’ confidence, risk tolerance, and strategic judgment. When technological change is relatively steady, as in Assertive Stability, leaders tend to believe they understand escalation dynamics, signaling pathways, and adversary responses with sufficient clarity. That confidence makes greater risk-taking and a more assertive U.S. nuclear posture appear both manageable and stabilizing, reinforcing the view that firmness and capability can be exercised without losing control.

By contrast, when technological change is disruptive, as in Adaptive Deterrence, uncertainty expands faster than shared understanding. Compressed timelines, opaque system interactions, and unclear escalation thresholds weaken leaders’ confidence in their ability to predict how actions will be interpreted or where escalation might lead. In this environment, caution becomes a stabilizing strategy. The United States is more likely to emphasize restraint, reassurance, and defensive signaling, not because threats are lower but because the costs of misinterpretation and unintended escalation are perceived to be higher.

This interaction helps explain why SLCM-N’s value varies across futures. Its utility depends less on the capability itself than on whether the strategic environment rewards flexibility and assertiveness or favors restraint and caution. The diagonal pattern therefore reflects an expectation that U.S. nuclear strategy adjusts to levels of technological uncertainty.