Arguments that the Navy should deploy a nuclear-armed sea-launched cruise missile (SLCM-N)—particularly arguments centered on low-yield characteristics—contribute important points to ongoing discourse about U.S. nuclear modernization.1 But there is more to consider than yield. Senior policy-makers need to understand SLCM-N in the context of a broader question: How should the United States bolster theater deterrence distinct from but reinforced by strategic deterrence?2
While yield matters, focusing on it diminishes other considerations and plays into established opposition. Recall that the 2022 Nuclear Posture Review (NPR) canceled SLCM-N in part because “the W76-2 low yield submarine-launched ballistic missile warhead, globally deployable bombers, dual-capable fighter aircraft, and air-launched cruise missiles” were considered sufficient for theater deterrence.3
There are three stronger arguments for SLCM-N than firepower per se. First, it improves theater deterrence options by decreasing reliance on aircraft-delivered weapons. Second, it could complement or replace the W76-2, distributing some of the theater deterrence role to attack submarines (SSNs) while reserving ballistic-missile submarines (SSBNs) for higher levels of conflict. Third, SLCM-N contributes to U.S. arms control, assurance, and nonproliferation objectives as complementary facets of U.S. nuclear strategy. These arguments align with the 2023 Strategic Posture Commission’s recommendations that “U.S. theater nuclear force posture should be urgently modified to: Provide the President a range of militarily effective nuclear response options to deter or counter Russian or Chinese limited nuclear use, . . . address the need for U.S. theater nuclear forces deployed or based in the Asia-Pacific, . . . [and] address allied concerns about extended deterrence.”4
Yielding Theater Deterrence
Theater deterrence is not a lesser included case of strategic deterrence. Deterring peer adversaries from limited nuclear use far from the U.S. homeland is different from deterring all-out nuclear strikes on the continental United States. This underlies the credibility issues with threatening large-scale retaliation for small-scale theater attacks. The United States abandoned such “massive retaliation” in favor of “flexible response” during the Kennedy administration. Since then, “U.S. presidents have sought a range of nuclear employment options so that they would not be forced into a choice of either ordering an all-out cataclysmic retaliatory nuclear attack or accepting that a nuclear attack would go unanswered.”5
Flexible response relies on philosophies about what “limited” means in the context of a nuclear exchange. “Limited war” does not refer only to limits on the political ends of a conflict; pursuing limited objectives with unlimited means is a recipe for escalating to total war. Rather, the concept must include limits on both ways and means—for example, which weapons are employed, from what platforms, and against what targets.6 Expanding the conflict along these dimensions is an escalation of intensity (vertical) or scope (horizontal). Conversely, mutually accepted restraints are the result of a tacit bargaining process that manages escalation and limits the overall war. This logic applies directly to theater deterrence predicated on possessing nuclear capabilities that are distinct from strategic weapons.
Paul Nitze wrote in 1956 that it is “to the interest of the West that the means employed in [nuclear] warfare and the area of engagement be restricted to the minimum level which still permits us to achieve our objectives.”7 The United States pioneered this understanding of theater dynamics during the Cold War, but Russia and China have been vigorously operationalizing it during the past decade. Nearly 70 years after Nitze’s comment, the Defense Department 2023 China military power report states, “[Chinese] military writings as of 2017 noted that while strategic nuclear weapons remain the foundation of deterrence, tactical nuclear weapons with high hit precision and smaller yield would be effective in lowering the cost of war.”8
If conflict crosses the nuclear threshold, lower yields would signal a clear interest in limiting its intensity. Fundamentally, yield is about the destructive force of the weapon—the effects it can impose on a target and its potential for collateral damage. A lower yield decreases a strike’s destructive force and therefore is a method of waging war with limited means. But defining a “low yield” threshold is notoriously difficult. Moreover, fixating on yield distracts from other important considerations.
The delivery system and host platforms are critical factors. Their combined capabilities and limitations govern responsiveness, tactics, logistics, vulnerabilities, command and control, and other operational requirements. How the United States addresses these requirements and thereby wields its theater deterrence platforms is a powerful source for signaling and shaping the limited nature of a potential nuclear exchange.
Controlling the weapon’s origin and flight path also signals limits on the conduct of nuclear exchanges. Adversaries will likely try to discern viable points of origin before a potential strike is launched and will almost certainly try to identify the origin after an attack. That information may be used to destroy the launch locations preemptively or in retaliation. This is one reason why U.S. intercontinental ballistic missiles (ICBMs), for example, are reserved for higher levels of destruction, stake, and resolve.
Lawrence Livermore National Laboratory’s Brad Roberts assesses that using theater-based weapons “might not be seen to be inviting or legitimizing a nuclear retaliatory strike on the American homeland.”9 In-theater platforms can deliver nuclear effects with fewer risks of horizontal escalation. By increasing options for the ways and means by which an attack is delivered, one gains flexibility in signaling and negotiating—kinetically, if need be—the limits of a conflict. This premise has likely informed Russia’s development of its theater nuclear arsenal and China’s reported interest in these capabilities.
Target choice is essential to signaling limitations. Targets must be valuable to the adversary, meet U.S. objectives, and be well-suited to nuclear effects but not so critical as to impel catastrophic escalation. This would be difficult in practice, however. Potential nuclear targets may have been destroyed or defeated earlier by conventional means. Others might have been intentionally avoided because of robust defenses or the risks of escalation and collateral damage. The degree of control for targeting is therefore a function of having weapons that can reliably reach a broad set of relevant maritime and terrestrial targets despite complex air-defense systems. This is even more important for tailored deterrence, which requires the ability to threaten a range of targets that differ by adversary and scenario.
Finally, deterrence success and deterrence failure have distinct playbooks, but they are mutually reinforcing and must be considered simultaneously. This paradox is especially relevant to theater dynamics and is why SLCM-N ultimately would help raise the nuclear threshold by ensuring potential adversaries see no possible advantage in limited nuclear escalation.
Diversifying Options
The U.S. nuclear weapon enterprise is dedicated to providing meaningful options for the President. Unfortunately, as the Strategic Posture Commission’s report shows, the current arsenal is suboptimal for theater deterrence. As nuclear policy expert Franklin Miller notes, “Nothing could be more dangerous than a president trying to manage a crisis with a nuclear-armed adversary assuming—and basing decision-making on—options that do not exist.”10
While the United States employs a robust nuclear triad for strategic deterrence, it relies on a near-monad of air-delivered capabilities for theater deterrence. Other than the W76-2, the NPR says the President’s options for theater deterrence are “bombers, dual-capable fighter aircraft, and air-launched cruise missiles.” These are valuable deterrence tools, and the justification for SLCM-N does not rest on being “more valuable” than them. Rather, it rests on “giving the President as many options as possible.” “Maintaining calculated ambiguity complicates an adversary’s decision calculus,” as Admiral Christopher Grady stated in 2021.11
Aviation assets are rightly lauded for their agility and scalable visibility and the option to recall them. Yet, for theater deterrence, they also bring several challenges. For one, launching a strike from a U.S. airfield poses concerns similar to those of launching an ICBM. Deploying aircraft and nuclear weapons forward to a theater requires airfields that can meet security, sustainment, and air-defense requirements. This demands deep cooperation with host and overflight nations—who may have reservations in peacetime, never mind in wartime. U.S. operations could expose them to preemptive or retaliatory nuclear strikes. Many allies willingly shoulder this burden as part of U.S. extended deterrence relationships and in recognition of greater threats from China and Russia. But prudence demands the President have options that are not contingent on local basing while minimizing risks to U.S. territory.
Deploying SLCM-Ns on board SSNs would do exactly that. It would offer a persistent, mobile, responsive platform that can launch from international waters outside allied territory and positions that minimize overflight requirements. Logistically, underway replenishments can keep SSNs at sea for long patrols. Whereas aircraft require a large degree of concentrated support in executing a nuclear strike (e.g., in-flight refueling, escort, suppression of enemy air defenses, etc.), SSNs can contribute to strike packages with minimal added signature and while remaining otherwise available for their conventional missions.
Given that U.S. forces are no longer structured to fight two major wars simultaneously, SLCM-N also would improve the President’s options for maintaining deterrence in a secondary theater. According to the NPR, “The Joint Force will need to be postured with military capabilities—including nuclear weapons—that can deter and defeat other actors who may seek to take advantage” of the U.S. military being principally engaged elsewhere. If such a scenario arises, deploying nuclear-armed SSNs to the secondary theater would impose fewer logistics and security burdens than deploying aircraft, which in any case might be needed for conventional operations in the primary theater.
Opponents argue that increasing theater-oriented nuclear options could encourage arms racing, incentivize nuclear warfighting, and invite a tit-for-tat escalatory spiral.12 The U.S. State Department’s Bureau of Arms Control, Verification, and Compliance rebutted such critiques in 2020, pointing out that, “while limited response options are not guaranteed to work, a massive response to a limited attack is even less likely to restore deterrence and more likely to spur further escalation.” The Bureau also notes that critiques often “conflate the possession of low-yield weapons with a doctrine of responding symmetrically. . . . The United States has no such doctrine.”13 Whether one views these statements as cognitive dissonance (both eschewing and threatening massive retaliation) or deliberate ambiguity, the fact remains that SLCM-N could significantly improve the President’s symmetric response options without constraining asymmetric ones.
Reserving Boomers
Credibly deterring and—if needed—waging limited nuclear war requires decoupling theater and strategic deterrence platforms. The United States relies on its SSBN force as the most survivable leg of its strategic nuclear triad and the guarantor of an assured second strike. Yet, as the only platform capable of delivering the low-yield W76-2 warhead, SSBNs could be called on early in a theater nuclear exchange. The SSBN force is thoroughly capable of this mission, but it would be a dangerous blurring of the line between theater and strategic roles, undermining efforts to demarcate the boundaries of a limited nuclear exchange.
By commingling theater and strategic weapons on SSBNs, the United States increases the risk that an adversary pursuing theater objectives could breach a red line by accidental, preemptive, or retaliatory targeting of an SSBN (read: strategic asset). If an adversary were to sink an SSBN, would the United States interpret that as strategic escalation? Even if the President did not prefer that interpretation, what retaliatory pressure might he or she perceive from military advisors, Congress, or allies and partners? In addition, any missile launched from an SSBN would expose its location and provide adversaries with a validated example of wartime procedures for the most survivable U.S. deterrence platform; an SSBN launch also might be misinterpreted as the beginning of a strategic attack. While SSBNs may never fully shed their theater deterrence role, it is unwise to risk these strategic assets during the earliest stages of a conflict if less vital platforms can be brought to bear.
Deploying SLCM-Ns on board attack submarines (SSNs) would bring important operational benefits. For one, there are many more SSNs that can be distributed in theater against only 14 Ohio-class SSBNs. Further, the 14 Ohio-class boats will eventually be replaced by just 12 Columbia-class SSBNs, each of which will have only 16 missile tubes, versus 20 per Ohio. Total SSBN tubes will decrease from 280 to 192—a little over 30 percent—putting a premium on magazine space that must be allocated to SLBMs for strategic deterrence missions rather than theater roles.14 While an adversary would have to assume all SSNs are nuclear armed, decoupling U.S. theater deterrence from strategic SSBNs would strengthen bulwarks for deterrence and improve escalation control options if deterrence fails.
Arms Control, Extended Deterrence, and Nonproliferation
Arms control, assurance, and nonproliferation serve the fundamental purpose of U.S. nuclear strategy—deterring aggression. These complementary endeavors reduce the number and type of nuclear threats for which the United States must account.
Arms control agreements reduce risks by negotiating limits on the means of warfare. For decades, nuclear agreements between Washington and Moscow protected strategic stability and constrained the threats each posed to the other, saving them from the costs of unconstrained competition. As arms control frameworks have degraded, the security environment has become more threatening, precarious, and expensive. Because China is not constrained by and refuses to discuss meaningful arms control, its role as a third peer in deterrence calculations exacerbates this.
Deploying SLCM-N would be an unmistakable signal of a U.S. commitment to safeguard itself and its allies by force when pressed. The Atlantic Council’s Matthew Kroenig suggests that if a new arms race is afoot, “It may be the type of arms race in which the United States must compete and win in order to protect itself and its allies.”15 However, deploying SLCM-N (along with other activities) would increase pressure on adversaries and could help revitalize arms control, much as deployment to Europe of U.S. Pershing II missiles in the 1980s encouraged negotiation of the Intermediate-Range Nuclear Forces Treaty. Rather than trade SLCM-N away, the negotiation objective should be an overall numerical cap on theater weapons. As Kroenig puts it: The United States “should view arms control not as an end in itself but rather as a useful tool that can be employed to advance U.S. and allied interests.”16
Last, extended deterrence goes hand in hand with nonproliferation. By minimizing the number of nuclear weapon programs in the world through cooperation on the peaceful uses of nuclear energy, extended deterrence guarantees, counterproliferation activities, etc., the United States is acting to protect its interests. Francis Gavin describes these “strategies of inhibition” as designed to favorably shape the strategic environment—hardly anathema to U.S. nuclear deterrence policy.17
Escalation Management
Submarine-based SLCM-Ns would be especially useful in the Indo-Pacific, where the United States lacks a permanent theater deterrence capability. They would signal the gravity of U.S. extended deterrence commitments and the ability to fulfill them without increasing risk to U.S. or allied territory. If deterrence fails, the United States could manage escalation by firing from the sea, thereby shifting some escalatory burden to the adversary by disincentivizing retaliatory strikes against targets ashore.
If a nuclear response is required, the President must have options to limit the scale and scope of a strike while the United States works to restore deterrence. SLCM-N would fill a gap in theater delivery capabilities necessary to meet that obligation.
Air Force General Anthony Cotton, commander of U.S. Strategic Command, affirmed the prospective value of SLCM-N, stating, “A low-yield, non-ballistic nuclear capability to deter, assure and respond without visible generation (similar to the characteristics of SLCM-N) offers additional options and supports an integrated deterrence approach.”18 Although the 2022 NPR canceled SLCM-N, renewing it would be consistent with the larger promise: “To deter theater attacks and nuclear coercion of Allies and partners, we will bolster the Triad with capabilities that further strengthen regional deterrence.”
1. CDR Paul Giarra, USN (Ret.), “Time to Recalibrate: The Navy Needs Tactical Nuclear Weapons . . . Again,” U.S. Naval Institute Proceedings 149, no. 7 (July 2023); and Brandon Patterson, “The Navy Needs a Low-Yield Nuclear Weapon,” U.S. Naval Institute Proceedings 148, no. 12 (December 2022).
2. The NPR primarily uses “regional” deterrence. “Theater” deterrence is arguably more appropriate because it conveys greater focus on deterring theater use by actors capable of strategic nuclear warfare while more clearly emphasizing escalation control.
3. Office of the Secretary of Defense, 2022 National Defense Strategy of the United States, including the Nuclear Posture Review and Missile Defense Review (Washington, DC: U.S. Department of Defense, 27 October 2022), media.defense.gov/2022/Oct/27/2003103845/-1/-1/1/2022-NATIONAL-DEFENSE-STRATEGY-NPR-MDR.PDF.
4. Congressional Commission on the Strategic Posture of the United States, America’s Strategic Posture (Washington, DC: Institute for Defense Analysis, October 2023).
5. Charles Glaser and Brian Radzinsky, “Basics of Deterrence and U.S. Nuclear Doctrine and Forces,” in Managing U.S. Nuclear Operations in the 21st Century, Charles Glaser, Austin Long, and Brian Radzinsky eds. (Washington, DC: Brookings Institution Press, 2022).
6. See Jeffrey Larsen, “Limited War and the Advent of Nuclear Weapons,” in On Limited Nuclear War in the 21st Century, Jeffrey Larsen and Kerry Kartchner eds. (Stanford, CA: Stanford University Press, 2014).
7. Paul H. Nitze, “Atoms, Strategy and Policy,” Foreign Affairs 34, no. 2 (1 January 1956).
8. Office of the Secretary of Defense, 2023 Report on Military and Security Developments Involving the People’s Republic of China (Washington, DC: Department of Defense, October 2023).
9. Brad Roberts, The Case for U.S. Nuclear Weapons in the 21st Century (Stanford, CA: Stanford University Press, 2016).
10. Franklin C. Miller, “Establishing the Ground Rules for Civilian Oversight,” in Managing U.S. Nuclear Operations, Glaser, Long, and Radzinsky eds.
11. “Senate Armed Services Committee Advance Questions for Admiral Christopher W. Grady” (Washington, DC, December 2021).
12. Andrew Reddie and Bethany Goldblum, “Evidence of the Unthinkable: Experimental Wargaming at the Nuclear Threshold,” Journal of Peace Research 60, no. 5 (September 2023): 760–76.
13. Bureau of Arms Control, Verification, and Compliance, Strengthening Deterrence and Reducing Nuclear Risks: The Supplemental Low-Yield U.S. Submarine-Launched Warhead (Washington, DC: Department of State, 24 April 2020).
14. Ronald O’Rourke, Navy Columbia (SSBN-826) Class Ballistic Missile Submarine Program: Background and Issues for Congress, 2 October 2023, crsreports.congress.gov/product/pdf/R/R41129.
15. Matthew Kroenig, The Logic of American Nuclear Strategy: Why Strategic Superiority Matters (New York: Oxford University Press, 2018).
16. Kroenig, The Logic of American Nuclear Strategy.
17. Francis J. Gavin, “Strategies of Inhibition: U.S. Grand Strategy, the Nuclear Revolution, and Nonproliferation,” International Security 40, no. 1 (2015): 9–46.
18. Bryant Harris, “New U.S. Nuclear Chief Takes Fresh Stance on Sea-Launched Cruise Missile,” Defense News, 14 March 2023.