The Nuclear Sea-Launched Cruise Missile: Worth the Investment for Deterrence

COMMENTARY Defense

The Nuclear Sea-Launched Cruise Missile: Worth the Investment for Deterrence

May 16th, 2022 25 min read
COMMENTARY BY
Patty-Jane Geller

Senior Policy Analyst, Center for National Defense

Patty-Jane is a senior policy analyst for nuclear deterrence and missile defense at The Heritage Foundation.
A Tomahawk land attack missile is launched from the USS Curtis Wilbur during a live-fire demonstration on May 27, 2019 in the Philippine Sea. Taylor DiMartino / U.S. Navy

Key Takeaways

The SLCM-N would provide a regionally present, sea-based, survivable option needed to fill a gap in U.S. nuclear deterrence capabilities.

While air-based nuclear weapons remain a critical part of U.S. strategy, a sea-based regional nuclear missile can bolster these existing regional capabilities.

Because nuclear deterrence is both the Navy and DOD’s number one mission, resourcing the SLCM-N should take priority.

INTRODUCTION

As part of the United States’ effort to modernize its nuclear forces to confront the growing nuclear threat, the 2018 Nuclear Posture Review (NPR) recommended restoring the nuclear-armed sea-launched cruise missile (SLCM). The United States previously deployed a nuclear SLCM (or SLCM-N), called the Tomahawk Land Attack Missile-Nuclear (TLAM-N) during the Cold War, but has since retired the capability. The NPR proposed the SLCM-N to adjust U.S. posture in response to Russia and China’s ongoing buildups of their regional, nonstrategic nuclear capabilities. The SLCM-N would provide a regionally present, sea-based, survivable option needed to fill a gap in U.S. nuclear deterrence capabilities. It would also improve allied assurance of U.S. extended deterrence commitments and add stability to an imbalance of regional nuclear forces that exists in both the European and Indo-Pacific theaters. Fielding the SLCM-N would require overcoming practical hurdles, including redeploying nuclear weapons on forward-deployed Navy ships, reallocating limited naval resources, and added costs. But ultimately, solving these challenges is feasible given the Navy’s previous experience deploying these weapon systems. Considering the immediacy of the nuclear threat and increased potential for limited nuclear use, investing in the SLCM-N is worth overcoming any practical difficulties

BACKGROUND

The SLCM-N is a theater-range cruise missile armed with a nuclear warhead that can be launched from surface ships or submarines. During the Cold War, the United States deployed the TLAM-N on surface ships and submarines from 1983 to 1991 as part of its strategy to deter a Soviet attack on Europe. In particular, the TLAM-N supported the strategy of deploying nonstrategic nuclear weapons to link conventional forces in Europe with the U.S. strategic nuclear arsenal. Because they were deployed in theater on submarines and surface ships, they helped assure allies that the United States’ extended nuclear umbrella would hold in the event of a Soviet attack. Additionally, the TLAM-N played an important role in deterring Soviet conventional or nuclear attack at a “middle rung” on the escalation ladder. While the United States deployed strategic systems to deter major strategic attacks and tactical systems such as nuclear artillery to deter conflict at the lowest rung of the escalation ladder, the TLAM-N helped fill this middle level, especially after the 1987 Intermediate-Range Nuclear Forces (INF) Treaty banned intermediate-range ground-launched missiles. Due to their survivability on stealthy attack submarines, the TLAM-N helped convince the Soviets that initiating conflict at this middle level of the escalation ladder would be met with an equivalent assured response.

After the Cold War ended, President George H.W. Bush withdrew the TLAM-N from service. It was kept in storage until 2010 when President Barack Obama’s NPR officially retired the capability. This decision was based on an assessment of the strategic environment at the time to be far more benign than the threats facing the United States today. But since then, the strategic environment has drastically shifted. While the United States dismantled its nonstrategic nuclear capabilities, Russia and China expanded them. Currently, Russia maintains at least 2,000 tactical nuclear weapons that are integrated into its doctrine of escalating conflict to compel its adversaries to back down. China is also advancing its theater-range missiles and rapidly growing its nuclear stockpile.

Rather than maintain the same nuclear posture meant for the previous strategic environment, the 2018 NPR recognized that U.S. posture must adapt to reflect the changed threat and proposed the development of two supplemental capabilities to increase the diversity and flexibility of U.S. nuclear forces. The first capability is a low-yield warhead for submarine-launched ballistic missiles (SLBM), the W76-2, which was deployed in early 2020. The second, long-term supplemental capability is to restore the SLCM-N within 10 years. The 2018 NPR required the Navy to conduct an Analysis of Alternatives for development of the SLCM-N. The AoA will answer questions on SLCM-N development and concept of operations, including the platforms on which SLCM-N will be deployed, the number of missiles to acquire, and whether the SLCM-N will utilize old TLAMs, technology from the LongRange Standoff Weapon program (LRSO), or new technology. To advance the discussion, this paper will assume that the SLCM-N can be deployed on attack submarines such as the Virginia-class and surface ships such as Zumwalt-class destroyers, as suggested by then commander of U.S. Strategic Command (STRATCOM) General John Hyten in 2018.

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For fiscal year (FY) 2022, Congress fulfilled President Joe Biden’s budget request of $5.2 million for the Navy to begin SLCM-N research and development efforts and $10 million for the National Nuclear Security Administration to begin work on an accompanying warhead, which will be an alteration of the W80-4 warhead currently being life-extended for the LRSO.7 The SLCM-N will likely take 7 to 10 years to deploy. While the Congressional Budget Office estimates that the SLCM-N might cost about $9 billion over 10 years, this assessment is very preliminary, and a more accurate cost will depend on the results of the AoA.9 The 2018 NPR called for reducing costs by taking advantage of existing technologies, so the extent to which SLCM-N utilizes technology from the LRSO currently under development or the Tomahawk missile has the potential to drive down costs.

STRATEGIC CONTEXT

The 2018 NPR proposed the SLCM-N to address the threat environment, which has changed dramatically over the past decade. The 2010 NPR claimed Russia to be no longer an adversary, and at that time there was still hope for China to rise peacefully. The 2010 NPR also established nuclear force modernization plans in line with the New Strategic Arms Reduction Treaty (New START) that the Department of Defense (DOD) is in the early stages of pursuing today. This current force structure reflects the more benign strategic environment of 2010, but Russia and China have significantly built up their nuclear forces since then. As STRATCOM commander Admiral Charles Richard recently noted, “For the first time in our history, the nation is on a trajectory to face two nuclear-capable, strategic peer adversaries at the same time, who must be deterred differently.” In addition, North Korea continues to improve its nuclear capabilities despite denuclearization efforts. Deterrence at a nonstrategic or regional level is becoming particularly challenging as Russia and China develop their nonstrategic nuclear capabilities while unconstrained by New START and North Korea bolsters its nuclear arsenal. While adversaries grow and advance their nuclear forces, U.S. nuclear posture remains static, as modernization plans consist of replacing existing systems on a one-to-one basis. Additionally, compared to adversaries’ nonstrategic arsenals, the United States only deploys a couple hundred B61 gravity bombs overseas that are not counted under New START.

To compensate for a perceived inferiority of conventional forces, Russia has sought to build a “deterrence ladder” that would enable it to employ nonstrategic nuclear weapons should the United States or NATO inflict unacceptable damage to its conventional forces. The 2018 NPR Russia maintains a diverse arsenal of delivery systems capable of carrying these nonstrategic weapons, ranging from short-range missiles to anti-ship cruise missiles, torpedoes, artillery, and potentially the defensive S-400 system.

China is also undertaking what Admiral Richard described as “a breathtaking expansion” of its nuclear forces. While China is completing a strategic nuclear triad accompanied by an assured second-strike capability, its advancement of regional nuclear forces means, as Richard noted, “they can do any plausible nuclear employment strategy regionally.” The People’s Liberation Army Rocket Force deploys several road- and rail-mobile ballistic missiles with medium and intermediate ranges that can strike an array of targets across the Indo-Pacific with precision. Most missiles are dual-capable, and the DF-17 missile might be able to carry a nuclear-capable hypersonic weapon. Additionally, China’s H-6K bomber can carry nuclear weapons, and China’s sea-based capabilities will improve with the development of the JL-3 SLBMs. These forces enable the Chinese to backstop their conventional forces in the region. For instance, should China decide to forcefully take Taiwan, it can use its regional nuclear forces to coerce the United States and constrain U.S. response options.

North Korea’s advancing nuclear capabilities will also increase the challenge of deterring nuclear use at the regional level. Despite diplomatic efforts, the Kim regime continues to produce fissile material to build more nuclear weapons. It maintains an arsenal of short- and medium-range ballistic missiles that can strike a range of targets in the Indo-Pacific. The presence of two nuclear-armed states increasingly hostile to the United States in the Indo-Pacific presents an increasingly complex strategic deterrence challenge to the United States.

THE CASE FOR THE NUCLEAR SLCM

The nuclear threat to the United States is unprecedented. Russia and China’s nuclear buildups indicate that they believe they can gain an advantage over the United States. So long as Russia and China continue to advance their regional nuclear forces and the United States simply maintains the same force posture designed for a different threat environment, this imbalance in regional nuclear forces will persist. As a result, the United States must take action to respond to this change in threat environment—doing nothing will jeopardize U.S. deterrence. The rest of this paper analyzes the 2018 NPR’s proposal to develop the SLCM-N in response to this change in threat, which the 2018 NPR states will provide a “needed nonstrategic regional presence” that will “strengthen the effectiveness of the sea-based nuclear deterrent force.”

What matters in determining a sufficient nuclear deterrent is the perceptions of adversaries of U.S. willingness to use nuclear force, not what the United States believes is necessary to deter. The argument for the SLCM-N is not necessarily that current U.S. forces are incapable of deterring Russian, Chinese, and North Korean regional nuclear threats, as it is impossible to know exactly why adversaries decide not to take certain actions. But because there is evidence that adversaries may believe they can gain an advantage by growing their nuclear forces or even employ their regional nuclear forces to compel the United States to back down in an ensuing conflict, more is needed to ensure certainty in the minds of adversaries that the United States can and will retaliate to even limited nuclear use. The SLCM-N has several unique attributes that would contribute to the credibility and flexibility of U.S. deterrence and allied assurance.

First, the SLCM-N can be deployed to the European or Indo-Pacific regions, increasing flexibility by providing the president with a proportional, credible response option. The SLCM-N will be deployed on sea-based platforms—likely destroyers or submarines—that can operate in theaters of conflict as opposed to U.S. strategic nuclear forces such as intercontinental ballistic missiles (ICBMs) located in the U.S. homeland or SLBMs deployed from nuclear ballistic missile submarines further out at sea. Russian and Chinese nonstrategic or regional nuclear buildups and strategies indicate that they may incorrectly perceive the United States to be reluctant to retaliate against a limited strike using a strategic nuclear weapon, which may disproportionally escalate the conflict further, and instead back down.24 While the United States may be confident in its ability to respond using strategic systems, what matters for deterrence is what adversaries perceive. Deploying a regional nuclear system that can more proportionally respond to limited nuclear employment can convince adversaries with more certainty of U.S. willingness and capability to respond to even a limited nuclear attack.

The need for a regional nuclear capability is especially acute in the Indo-Pacific theater, where the United States does not forward deploy any nuclear weapons. To respond to nuclear employment at the lower rungs of the escalation ladder in the Indo-Pacific, the United States would need to respond with a strategic nuclear weapon or relocate tactical weapons to the theater. While one cannot definitively say whether adversaries will view U.S. ICBMs, SLBMs, and strategic bombers as a credible deterrent against their tactical nuclear weapons, Russia and China’s massive regional nuclear force buildups indicate that they believe they can gain an advantage over the United States—an advantage that the United States must seek to limit. As the threat of regional nuclear forces grows, the SLCM-N can convince an adversary with more certainty that any nuclear use will be met with a proportionate U.S. response. The key is affecting threat perceptions in an enemy’s mind that the United States has viable options all along the escalation ladder that it can employ, not a quantitative matching of warheads.

Critics argue that the existing nuclear triad suffices to deter the growth in China and Russia’s nuclear capabilities, especially since the United States deployed the W76-2 low-yield SLBM in 2020. However, keeping U.S. force posture “as is” will allow this imbalance to persist in regional nuclear forces—which is profoundly destabilizing. The SLCM-N provides a unique capability to deter this growth in threat because it is nonstrategic, not limited to New START’s numeric caps, and can be forward deployed to directly deter adversary regional systems. The W76-2 provided a limited capability to have an option for a more proportional response to low-yield nuclear use in the short term, but more is needed to address the ongoing numeric growth in Chinese and Russian nuclear arsenals. Since it is not treaty-constrained, the SLCM-N enables the United States to add more deployed nuclear systems in the longer term to ensure the United States maintains sufficient capacity to deter the growing threat. Additionally, while the W76-2 provides a useful option to respond with a low-yield weapon, a regionally present system may be a more appropriate response for many limited-use scenarios than a launch from a strategic SLBM.

Second, because the SLCM-N will be deployed on a sea-based platform, it adds a more survivable option to U.S. capabilities below the strategic nuclear threshold. Currently, the United States’ only systems that can be forward deployed are air-based. In Europe, the United States forward deploys a couple hundred B61 tactical nuclear gravity bombs that can be deployed on either U.S. fighters or NATO dual-capable aircraft. However, the storage locations of these bombs are known and therefore vulnerable to Russian attack. Without enough warning time during a crisis, Russia can destroy those bombs, leaving the United States without this option. In the Indo-Pacific, the United States does not forward deploy any nuclear weapons to counter the growing Chinese nuclear threat. The United States can send nuclear-capable bombers to both regions during a crisis, but doing so requires long flight times and avoiding advancing air defenses. In fact, advancing adversary anti-access/area denial (A2/AD) environments indicates that adversaries may find U.S. air-based capabilities to lack credibility. According to a DOD report:

Given the major investment both Russia and China have made in A2/AD capabilities (especially advanced integrated air defense systems), each may come to believe it can effectively impede U.S. regional nuclear capabilities in executing their deterrence missions and thereby secure an exploitable coercive advantage. Dual-capable aircraft may be vulnerable, or perceived as vulnerable, to advanced defensive systems despite enhancements to their stealth and standoff features.

While air-based nuclear weapons remain a critical part of U.S. strategy, a sea-based regional nuclear missile can bolster these existing regional capabilities by more effectively operating against Russian and Chinese air defense systems. Sea-based, survivable submarines or even destroyers can operate in an extensive area and are difficult to find and destroy. Submarines are difficult to detect, and even Navy destroyers dispersed throughout the waters can make targeting difficult, especially if they have low observable characteristics, such as the Zumwalt-class. They can also operate in regional seas during both peacetime and crisis; they do not require long periods of time to deploy. As bombers, fighters, and their bases remain vulnerable to improving enemy A2/AD capabilities, the United States needs an additional regional nuclear option that is sea-based. The argument is not that the SLCM-N on sea-based platforms would be impervious to detection and attack compared to air-based nuclear forces, but rather that expanding options would improve the U.S. deterrence posture by making an adversary’s attack calculus more complicated.

Third, a SLCM-N’s cruise missile trajectory contributes to the U.S. ability to effectively hold targets at risk and complements ballistic missile options. For deterrence to be effective, the United States must ensure it can credibly hold targets at risk. Sea-launched cruise missiles fly at low altitudes, making them much more difficult to detect and intercept by adversary air defenses. The SLCM-N missile itself may incorporate advanced stealth capabilities if it is designed similarly to the LRSO. Ships can also launch multiple cruise missiles from multiple platforms simultaneously at independent targets, which complicates adversary air defenses and strengthens deterrence. This capability is similar to the ALCM, which also flies on a cruise missile trajectory, but is complementary, rather than redundant, especially considering adversary efforts to make airspace for bombers and fighters increasingly prohibitive. Additionally, unlike bombers that cannot remain in the same position for a long period of time without risk of being shot down, sea-based platforms can loiter close to targets. This attribute makes SLCMs particularly effective for striking time-sensitive targets. For instance, Russia, China, and North Korea all rely on the use of transporter erector launchers (TELs) to load and launch their mobile ballistic missiles. The SLCM-N can strike these targets promptly.

Therefore, the SLCM-N complements U.S. ballistic missiles—and the W76-2 low yield weapon in particular—by forcing the adversary to contend with missiles flying on both trajectories, in addition to missiles launched from both air and sea. This is not to argue that the United States cannot target time-sensitive targets such as TELs with other nuclear capabilities today or that a cruise missile would perform better than other capabilities. Rather, the SLCM-N increases the uncertainty and risk in adversaries’ behavior, as having to deal with both kinds of threats increases the demands on their advancing defense systems. Additionally, given the rapidly advancing threat and the time it takes to deploy new capabilities, commencing efforts now to increase the clarity in U.S. capability and will to respond is essential. Fielding the SLCM-N sends a strong signal that the United States will not tolerate regional aggression.

A regional, sea-based, cruise missile option would play an important role in both the European and Indo-Pacific theaters by convincing adversaries that attempts to escalate conflict will bring unacceptable risk. During the Cold War, the TLAM-N limited Soviet options for destroying U.S. forces deployed in Europe because even if the Soviets destroyed all the U.S. intermediate-range nuclear missiles, they could never be sure they could locate and destroy TLAM-Ns. In fact, the former commander of the U.S. Sixth Fleet, Vice Admiral J. D. Williams, recalled Soviet leader Mikhail Gorbachev remarking in a meeting with U.S. president George H.W. Bush that: “We have read every one of your submarine messages for ten years and have been unable to find or kill even one of them. We quit.” Now, the United States does not even deploy nuclear missiles to Europe—only B61 bombs, of which Russia knows the locations. With more survivable SLCM-Ns lurking in regional waters, Russia would have to think twice before escalating conflict to the point where it believes it can employ nuclear weapons and win.

The SLCM-N may play a more critical role in the Indo-Pacific theater. The dual-capable nature of China’s theater-range ballistic missiles combined with its advancing early-warning and command and control capabilities indicate that its nuclear forces could backstop a strategy to take Taiwan and compel the United States to back down during a crisis. China’s growing regional nuclear forces can constrain U.S. response options if the United States cannot effectively deter nuclear use at the lower end of the escalation ladder. According to Admiral Richard, “We’ll be the ones that are getting deterred if I don’t have the capability to similarly deter them.” It is important to note that effective deterrence depends on the successful completion of the modernization of the entire U.S. nuclear enterprise—including warheads, delivery platforms, and command and control systems—but as a part of that effort, the deployment of SLCM-Ns would fill an important gap that exists today.

SLCM-N AND ALLIED ASSURANCE

Allies may question the credibility of a U.S. response to limited employment of nuclear weapons in Europe or the Indo-Pacific using its high-yield, strategic nuclear forces. They may also question U.S. assurance commitments in general should the United States ignore the growing disparity with Russia and China. A nuclear capability that can be deployed in allies’ own regions can help reinforce that the United States is committed to the extension of its nuclear umbrella. Additionally, because it is sea-based, the SLCM-N can provide this benefit without the need for additional basing requirements. For this reason, NATO and Pacific allies would likely support the SLCM-N because it would improve deterrence of their aggressive neighbors without provoking domestic protests against nuclear weapons basing.

Maintaining allied confidence in the U.S. nuclear umbrella is critical as allies in Europe, and even more so the Indo-Pacific, become increasingly threatened by Russian and Chinese aggression. For instance, former commander of U.S. Indo-Pacific Command Admiral Philip Davidson predicts that China could invade Taiwan within the next six years. At the same time, allies have reason to doubt U.S. commitments to extended deterrence, as the United States has sought to minimize its role in the world over the course of recent administrations. If the United States cannot modernize and maintain force levels of its own nuclear forces, allies will likely question the U.S. commitment to maintaining a nuclear force capable of deterring attacks against allies as well. Especially as allies such as Japan and South Korea have the technical capabilities to produce their own nuclear weapons, the United States must ensure its extended deterrence commitment remains credible. Developing the SLCM-N would aid in this effort.

SLCM-N AND STABILITY

Critics of nuclear deterrence argue that the SLCM-N will negatively impact stability with U.S. adversaries or start an arms race. China and Russia’s nuclear buildups threaten strategic stability. Their expanding and diversifying arsenals may provide both nations options to escalate conflicts in novel ways to which the current U.S. nuclear posture would be challenged to respond. This trend erodes deterrence; China and Russia may be more willing to take risks or even strike first as the credibility and efficacy of a U.S. response diminish. Adding the SLCM-N to the U.S. arsenal is therefore stabilizing because it would begin to rectify this imbalance.

The SLCM-N would also not start an arms race. Both Russia and China are already expanding their nuclear forces, as well as developing new and novel nuclear systems. The SLCM-N is a modest response to these significant expansions—and would not be the cause of them. Senior military leaders have also consistently emphasized that the United States does not intend to match either nation system for system; however, doing nothing means ceding an advantage to adversaries and reducing the United States’ ability to deter nuclear use. Russia and China will of course seek to disparage the SLCM-N effort as destabilizing. Doing so is in their interest since the SLCM-N would help close in on the advantages they seek—not because it would disrupt any existing strategic stability that Russia and China have already been acting to squander.

Another concern is that because the United States also deploys conventionally armed cruise missiles, Russia or China will confuse a U.S. conventional cruise missile with a nuclear one and launch a nuclear attack in response. However, the logic that a state can characterize a warhead based on missile trajectory is fundamentally flawed when it is technically possible to put a nuclear payload on any type of delivery system. This problem is also not unique to the SLCM-N, as countries have deployed dual-capable weapons for years and this mistaken escalation has never occurred. In an escalating conventional conflict, a Russian or Chinese preemptive nuclear strike after a U.S. cruise missile launch is implausible. Because Russia and China have clear assured second-strike options available after a U.S. missile launch, preemptively launching nuclear weapons and risking nuclear retaliation when a chance exists that the U.S. missile launch was conventional would not be a rational response.

SLCM-N AND ARMS CONTROL

Developing the SLCM-N may also play a useful role in future arms control negotiations. The NPR states that the SLCM-N “may provide the necessary incentive for Russia to negotiate seriously a reduction of its non-strategic nuclear weapons.” Russia has historically refused to even discuss its growing nonstrategic nuclear stockpile, much less negotiate on numbers and types. The Trump administration reached an agreement in principle for Russia to freeze all nuclear warhead growth in exchange for a short-term New START extension, but Russia reneged on that agreement after the U.S. 2020 election. Just as the U.S. deployment of Pershing II intermediate-range ballistic missiles in Europe led to the INF Treaty in 1987, SLCM-N deployment—or even mere development—might compel Russia to the negotiating table. Deploying the SLCM-N may have a similar impact on China, which has thus far refused to participate in arms control discussions. Moreover, failing to respond to either nation’s nuclear buildups would likely decrease adversaries’ incentives for meaningful arms control by reinforcing their views that expanding their nuclear forces provides them a military advantage.

To be clear, the SLCM-N ought not be developed solely for the purpose of eventually being negotiated away. Given Russia and China’s regional nuclear force buildups, the United States should pursue the SLCM-N to help deter these threats. As General John Hyten testified when he was STRATCOM commander in 2018, “That [SLCM] capability is against the threat. However, that capability also gives our negotiators something to talk about. If you do not have something to talk about, it is very hard to sit down and negotiate. But it is not a bargaining chip because it is to counter the threat.”

PRACTICAL CONSIDERATIONS TO ADDRESS

The case for the SLCM-N’s contribution to deterrence and national security is clear, as initially made by the 2018 NPR. The more important questions and concerns lie in the practical and feasibility implications of acquiring the SLCM-N. DOD will have to decide on which platforms it will deploy the SLCM-Ns, where any outcome would likely impact critical conventional naval missions. The Navy will also need to fit the SLCM-N into an already-constrained budget. While decisions such as platform, number of missiles, missile technology, and concept of operations have been examined in the AoA, this paper discusses potential options and outcomes to inform future policymaking. Ultimately, while developing the SLCM-N will require trade-offs, its development would provide a significant operational impact and is possible at a low cost.

The SLCM-N will likely be deployed on surface ships, attack submarines, or a combination of the two. In 2018, General Hyten specified that DOD would examine deploying SLCM-Ns on different types of submarines and the Zumwalt-class destroyer. While the Ohio-class, or future Columbia-class SSBNs, will likely not be an option, the Virginia-class attack submarines (SSNs) would be the likeliest candidate for submarine deployment. The U.S. Navy currently maintains 19 Virginia-class boats and will continue procuring about two more per year as the older Los Angeles-class SSNs retire. The Virginia-class has both vertical launch tubes and torpedo tubes that can carry the conventional TLAMs. Most Virginia-class boats being procured now and in subsequent years will carry the new Virginia Payload Module (VPM), an 84-foot-long section that can carry additional missile tubes, increasing capacity for missiles by about 76 percent. Given the Cold War experience of deploying SLCM-Ns, it is very plausible that new versions of this weapon could approximate the size of TLAMs and presumably fit in the VPMs or torpedo tubes of the Navy’s submarines.

As hinted by General Hyten, the Zumwalt-class destroyer (DDG-1000) could also deploy SLCM-Ns. The Navy owns three Zumwalt-class ships, with no plan for further procurement. The mission of the Zumwalt-class has recently expanded to include both surface warfare and land-attack capabilities. It carries the 80-cell Vertical Launch System capable of carrying TLAMs, making it a strong candidate for carrying SLCM-Ns. Surface ships can be seen and tracked, which would increase their vulnerability during conflict, but they can provide a powerful deterrence signal to U.S. adversaries. If deployed to the Indo-Pacific, announced in April 2021 that one of the Zumwalt-class ships would carry the Navy’s Common Hypersonic Glide Body, which would require missile tube alterations to fit the larger hypersonic missiles. Acquiring the hypersonic mission would not rule out the SLCM-N mission—if anything, carrying both systems would fit the Zumwalt’s new mission of blue-water strike. However, limited space on the Zumwalt-class may require trade-offs in the number of hypersonic versus nuclear cruise missiles it can hold. While this trade-off may be offset by future deployment of hypersonic missiles on the VPMs, policymakers will need to consider capacity limits.

Indeed, policymakers have already expressed concern with the SLCM-N detracting from core naval missions, “such as tracking enemy submarines, protecting United States carrier groups, and conducting conventional strikes on priority land targets,” according to introduced legislation. The Navy will also lose missile tubes when the Ohio-class guided-missile submarines (SSGNs) retire in the FY 2026 to FY 2028 timeframe. While the VPMs are intended to make up for lost space provided by the large SSGNs, the Navy’s total missile capacity will still decrease.

Deploying nuclear weapons on conventionally armed platforms brings several issues because DOD manages nuclear weapons differently than conventional weapons. Nuclear and conventional weapons use different fire control systems, requiring the Navy to add fire control stations to conventional ships that would deploy SLCM-Ns. Nuclear weapons management also requires separate personnel training and special security measures. Adding nuclear weapons to conventional ships is not as simple as inserting the missiles into tubes—doing so involves additional, hidden costs.

While these challenges are significant, the Navy can consider potential arrangements to find an amenable concept of operations, as it did during the Cold War. To avoid nuclear certification complications, the Navy could retrofit a block of submarines as dedicated SLCM-N carriers. But that could constrain those submarines from conducting their existing conventional missions. Instead, the Navy might retrofit a portion of its attack submarines to carry SLCM-Ns in addition to conventional weapons, allowing those boats to continue their conventional missions. During the Cold War, the deployment of TLAM-Ns on ships along with conventional missiles did not change the ships’ general mission to implement the Navy’s maritime strategy. One advantage of this option is that U.S. adversaries would not know which boats carried nuclear weapons, increasing uncertainty and deterrence. Indeed, much of the SLCM-N’s contribution to deterrence may be achieved with a relatively modest deployment, creating another opportunity to manage trade-offs.

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While delivery platform selection and nuclear certification processes may be complex and create additional costs, development of the missile itself may be simpler. Because the SLCM-N is not a new capability, the Navy can exploit existing technology and know-how to build the SLCM-N. As former secretary of defense James Mattis stated, “[B]y going back to a weapon that we had before, there is a fair amount of already sunk technology costs that we will not have to redo, will not have to come back up and ask for again.” The $9 billion cost estimated by the Congressional Budget Office is based on an assumption that the SLCM-N would be similar to the LRSO. However, the Navy has the option to simplify the SLCM-N development even further by just updating the TLAM-N. Even if the Navy does opt to build a brand-new missile, it could minimize costs by leveraging the technologies used to build the LRSO. In fact, the National Defense Authorization Act for FY 2020 required that DOD report on opportunities to do just that.57 The decision to alter the W80-4 Life Extension Program (the warhead being developed for the LRSO) to fit the SLCM-N could also help minimize costs and simplify the effort. While deploying SLCM-Ns on ships may require additional burdens and costs, the Navy does not need to reinvent the wheel to develop the SLCM-N itself.

CONCLUSION

Ultimately, while issues with nuclear certification, personnel training, and resource allocation present valid challenges, they are not insurmountable and are worth resolving, considering the SLCM-N’s role in deterring the advancing global nuclear threat. Evidence is growing that nuclear war is likeliest to begin at the lower levels of the nuclear escalation ladder in either the European or Indo-Pacific theaters. Regional nuclear forces could also be used to coerce and constrain U.S. response options. This rising threat must serve as the prime driver for U.S. deterrence strategy. Because the SLCM-N can be deployed on a sea-based platform to the theater of conflict and provide a survivable cruise missile option, it can help convince both U.S. adversaries and allies of the United States’ will and capability to respond to a limited, regional nuclear strike. In this sense, it would increase stability among peers by helping to offset an imbalance between U.S. and adversary regional nuclear forces.

Practical considerations such as cost and resource allocation should not preclude the execution of this threat-driven strategy. While indeed challenging, concepts of operations for SLCM-N deployment exist that could lessen the burden on the Navy. The Navy has deployed SLCM-Ns before and can do so again. Even if future budgets remain constrained, the Navy can prioritize SLCM-N development at the lowest cost possible. Because nuclear deterrence is both the Navy and DOD’s number one mission, resourcing the SLCM-N should take priority. Ultimately, the United States must adjust its force posture in some way to respond to the change in nuclear threat, and the modest addition of the SLCM-N could have a significant impact on U.S. national security.

This piece originally appeared in On the Horizon