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In recent months, intensifying conflict around the world has called new attention to the possibility of military confrontation between nuclear-armed states. To meet these challenges, the United States is engaged in a substantial modernization of its own nuclear capabilities, including a new nuclear-armed cruise missile for its submarine force, commonly referred to as “SLCM-N,” or sea-launched cruise missile–nuclear. For several years, American strategists have debated the wisdom of this weapon. Critics argue that the missile poses steep opportunity costs, both in terms of the industrial resources necessary to build the weapon and in the scarce operational assets on which it would be deployed. Proponents of the missile reply that the U.S. Navy has deployed nuclear cruise missiles before, and that there is no reason it should not be able to do so again.
Both sides are ultimately correct: A nuclear sea-launched cruise missile is both possible and costly. Balancing these two perspectives ultimately requires us to go back to strategy, to understand how the United States uses its nuclear forces. This is a more complicated question than is sometimes assumed, because American nuclear strategy has changed significantly over time. During the Cold War, American nuclear strategy deterred the Soviet Union with the threat of rapid American nuclear escalation. For this strategy, widely proliferated nuclear weapons, including nuclear cruise missiles aboard submarines, made a great deal of sense.
Today, however, the United States does not rely so heavily on nuclear threats. While American declaratory policy does not rule out nuclear first use, the United States places a clear emphasis on deterrence through conventional preponderance below the level of nuclear employment. Nuclear submarine cruise missiles do little to advance this strategy beyond existing capabilities. Given current American strategy, the costs of a nuclear-armed cruise missile for submarines clearly outweigh any benefits. Industrial and operational resources should be directed to more pressing concerns like strategic nuclear modernization and conventional deterrence in the Taiwan Strait.
Capabilities and Costs
The dispute over a sea-launched nuclear cruise missile goes back years. The weapon was first proposed by the Trump administration in its 2018 Nuclear Posture Review. In 2022, the Biden administration tried to cancel the missile, but Congress continued to fund its development. The current Trump administration recently awarded contracts to five companies to develop missile prototypes in the coming years.
Proponents of the new missile put forward several arguments. First, improving American theater nuclear capabilities would enhance escalation control by providing American leaders with more options to respond to an adversary’s nuclear escalation. Second, diversifying American theater nuclear capabilities would increase their survivability and reliability. Third, robust theater nuclear capabilities reassure allies.
Some critics object to a new nuclear-armed cruise missile on principle. They allege that the missile will undermine “strategic stability” by providing more nuclear options to policymakers. They also worry that many different weapons on submarines could decrease the ability of the United States to signal restraint. Of course, proponents argue that nuclear options will stabilize crises through escalation control, including submarine-launched weapons. Given the ambiguity of “strategic stability,” proponents and opponents of the missile are unlikely to agree regarding its contribution to stability.
More concretely, other opponents criticize the weapon’s cost. First, there is the $10 billion price tag — small when compared to overall nuclear modernization, but substantial compared to many competing priorities. More importantly, a new nuclear cruise missile would pose opportunity costs for the American defense industry. The United States struggles to produce enough missiles. American nuclear industrial capability faces even steeper challenges, with the National Nuclear Security Administration struggling to meet deadlines to modernize the existing nuclear stockpile. Even if money is available, additional orders risk impeding other high-priority programs.
A new cruise missile also poses operational costs for submarines. The United States is struggling to scale up construction of attack submarines. As such, major changes to missions — like integrating a new nuclear-armed cruise missile — will result in further reduction in submarine availability.
Proponents of this missile disagree and often point out that the United States deployed nuclear cruise missiles aboard submarines in the 1980s — known as the nuclear Tomahawk — without fatal industrial or operational dislocation. The result is a debate in which the two sides talk past each other, with one side emphasizing improved capabilities and the other focusing on costs.
Missiles and Strategy
The tension between capability and cost requires reexamining the shifting role of nuclear weapons in U.S. strategy. In the Cold War, Washington planned to use nuclear weapons first to offset Soviet conventional superiority, later evolving toward “flexible response” with theater and limited strategic nuclear options. This posture drove a vast arsenal with strategic, tactical, and theater weapons such as the nuclear Tomahawk. These were designed both to threaten escalation while at the same time signaling restraint by withholding strategic nuclear forces.
American strategy changed, however, with the end of the Cold War. The collapse of Soviet power and the decisive victory in the Persian Gulf suggested that the United States now enjoyed advantages in conventional conflict. While the United States did not renounce the use of nuclear weapons, it radically reduced the role that nuclear weapons played in its security and defense strategies. Instead, American strategists saw the defeat of adversary conventional forces as the primary deterrent of aggression, with nuclear weapons supporting conventional overmatch by deterring adversaries from escalating their way out of a losing conflict. As a result, theater nuclear capabilities were curtailed in favor of a greater focus on conventional warfighting. One casualty of this restructuring was the nuclear Tomahawk, which was removed from American submarines in 1992, though not fully dismantled until 2010.
The continued ambiguity of American nuclear declaratory policy does not override the trend towards conventional deterrence. American leaders have not adopted a “no first use” policy — in principle, the United States might employ nuclear weapons first in defense of its supreme national interests. The retention of the right to employ nuclear weapons first, however, does not mean that American intentions regarding nuclear employment remain the same. The increasing reliance on conventional deterrence as a cornerstone of American strategy stands in sharp contrast to the Cold War, where the United States retained not only the right but repeatedly broadcast the intention to employ nuclear weapons in a major conflict early and often.
Escalation Control
The evolution of U.S. strategy from the Cold War to today highlights “escalation control,” a key advantage attributed to a submarine-launched nuclear cruise missile. However, escalation control means different things to different strategies. During the Cold War, escalation control meant enabling nuclear escalation at lower levels of intensity without having to “go big.” Under that strategy, the logic of escalation control did require diversified theater nuclear capabilities, not to respond to an adversary’s first strike but to credibly threaten to initiate nuclear conflict. Indeed, this imperative for escalation control explains the asymmetry between current American nuclear forces and those of Russia, which still relies on the proactive threat of low-level nuclear employment.
By comparison, American strategy since the 1990s does not rely primarily on the threat of nuclear escalation: Today, “escalation control” means deterring adversary use of nuclear weapons. This requires deterring adversaries — even those facing significant conventional defeat — from escalating to nuclear use. U.S. conventional capabilities will only matter if the United States can control escalation. Otherwise, American leaders will constrain U.S. forces in ways that undermine their effectiveness. For example, in the late 1960s the Johnson administration put significant limits on American conventional operations in Southeast Asia to avoid adversary escalation. Studies conducted at the time emphasized not the vulnerability of the American homeland to attack (given China’s then-anemic intercontinental capabilities), but rather the vulnerability of U.S. forces in Southeast Asia themselves. Deterring adversaries from escalating when they are losing conventionally and reassuring leaders that they can fight and win despite adversary threats is a tall order.
Under current strategy, a submarine-launched nuclear cruise missile competes with too many higher priorities, the first being conventional forces. Successful conventional deterrence is the most effective tool for controlling escalation and avoids the circumstances in which escalation might occur in the first place. U.S. attack submarines are one of the most important tools for conventional deterrence. A submarine-launched nuclear cruise missile that reduces conventional deterrent capabilities does not contribute to American strategy.
The second priority is the modernization of American strategic nuclear forces. Should conventional deterrence fail, escalation control will depend first on strategic forces — not theater nuclear weapons. This is because the main purpose of theater nuclear weapons is to threaten escalation to all-out nuclear war. At various points, American, Russian, French, Israeli, and Pakistani strategists have relied on theater nuclear weapons to risk all-out escalation in this way. Faced with nuclear blackmail, the balance of theater forces is far less important than the willingness to risk escalation. As a result, the way to control escalation is to convince adversaries that the United States would prevail in an all-out nuclear war. Adversaries who anticipate defeat in strategic nuclear war will have little incentive to risk its eruption through theater nuclear attack. Scarce industrial resources should be directed towards the modernization and expansion of U.S. intercontinental ballistic missiles, ballistic missile submarines, and long-range bombers, not submarine-launched nuclear cruise missiles.
The third priority is that American forces be able to keep fighting after a nuclear attack. Aside from their coercive role, theater nuclear weapons can inflict tremendous damage on concentrated forces. Retaliation in kind does little to deter this, since the adversary would still reap the benefits of disrupting American operations. More important than in-kind reprisal is the ability to keep fighting and winning at the conventional level even after a nuclear attack. Resilient conventional forces can deny adversaries the military benefits of nuclear employment. They also reassure American decisionmakers to fight with the aggressiveness necessary to prevail. The United States needs conventional capabilities that can be dispersed or concealed against nuclear attack — capabilities like attack submarines, long-range aviation, and perhaps new concepts for survivable massed fires.
The ability to respond in kind to adversary theater nuclear employment is thus a fourth priority. Listing American theater nuclear capabilities as a fourth priority is not to deny that they are a priority that can play an important role. Given the unavoidable tradeoffs of expanding theater nuclear forces with higher priorities in strategic and conventional capabilities, however, the United States should focus on existing or incoming weapons that place less strain on industrial and operational resources. These include the Trident W76-2, the B61 gravity bomb, and the AGM-181 — which, unlike a submarine-launched weapon, contributes to strategic nuclear modernization. Given current American strategy, it makes no sense to quadruple-down on theater nuclear weapons at the expense of conventional or strategic nuclear forces.
Conclusion
Given its limited contribution to current American strategy, the costs of a submarine-launched nuclear cruise missile outweigh its benefits. Proponents of a new cruise missile are correct that the United States deployed such a weapon in living memory. That was then — today, the United States does not rely on the threat of early nuclear escalation to deter adversaries. Instead, current American strategy requires powerful strategic nuclear forces to control escalation and powerful conventional forces to defeat adversaries, if necessary. Theater nuclear forces are a distinctly lower priority. It makes little sense to expend scarce resources on a new submarine-launched nuclear cruise missile while the two higher priorities remain uncertain. The United States should focus scarce nuclear industry on strategic modernization. Submarine- and sea-launched cruise missiles should go to theater conventional missions, where they play critical roles.
A submarine-launched nuclear cruise missile might make sense for a different sort of strategy. If the United States ever reverted to regular threats of nuclear escalation, as it did in the Cold War, then proliferating nuclear cruise missiles would support American strategy, even as the wisdom of such a strategy would bear close scrutiny. Developing a new nuclear cruise missile for submarines might therefore make sense as a hedge against a future change in strategy. Under current strategy, however, deploying a new nuclear cruise missile aboard submarines should not be a priority.
John D. Maurer is a professor at the School of Advanced Air and Space Studies at Air University and a nonresident fellow at the American Enterprise Institute. The views expressed are those of the author and do not reflect the official policy or position of the U.S. Air Force, Department of Defense, or the U.S. government.
Image: Mass Communication Specialist 1st Class Ronald Gutridge via DVIDS
