Trade-offs always arise for states deciding whether to spend billions of dollars on a new weapon system, and the nuclear-armed sea-launched cruise missile (SLCM-N) is no exception. In the United States, proponents of this weapon have not made detailed arguments in its favor, but their main assertions are that the country needs some unspecified number of SLCM-Ns to deter Russia from invading a NATO country and China from attacking Taiwan—a so-called deterrence gap.

George Perkovich
Perkovich works primarily on nuclear strategy and nonproliferation issues; cyberconflict; and new approaches to international public-private management of strategic technologies.
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Congress should question such assertions. The nuclear-armed SLCMs would not be buildable until the early 2030s, so there is time for serious debate. Meanwhile, the United States already has or will soon have three other nuclear weapon systems with similar capabilities: new B61 nuclear bombs, current and in-production air-launched cruise missiles, and the new W76-2 low-yield warhead on Trident D5 submarine-launched ballistic missiles. These systems can, together, do anything the SLCM-N can do.

Is There a Demonstrated Need for the SLCM-N?

Admiral Charles Richard, commander of the U.S. Strategic Command (STRATCOM), offered in an April 4 letter to the Senate Armed Services Committee the most detailed assertions in favor of the SLCM-N. He said,

“While I am satisfied USSTRATCOM priorities are adequately addressed, the current situation in Ukraine and China’s nuclear trajectory convinces me a deterrence and assurance gap exists. . . . To address this gap, a low-yield, non-ballistic capability to deter and respond without visible generation is necessary to provide a persistent, survivable, regional capability to deter adversaries, assure allies, provide flexible options, as well as complement existing capabilities.”

The artifice of Richard’s pitch—suggesting that one weapon needs all five attributes he lists—betrays its weakness. Each of these explicit or implied assertions needs to be examined, especially because the United States already deploys weapons that meet four of Richard’s five criteria. The exception is “without visible generation,” and that criterion is met by the low-yield W76-2 warhead on Ohio-class submarines.

Congressional officials with sufficient clearances should inquire what high-value targets in Russia and China cannot be destroyed by the weapons in the existing arsenal but could be by the SLCM-N. My own answer to this question is “none.” Further, if the United States launched nuclear weapons at Russia’s and China’s most vital targets, President Vladimir Putin and President Xi Jinping and their respective successors would not respond differently if the incoming U.S. nuclear weapon was being carried by an SLCM-N or a D5 with warheads of similar yield. The destructiveness of the attack would be practically the same; the source of each would be a submarine in international waters.

If SLCM-N proponents suggest that Putin’s invasion of Ukraine demonstrates his willingness to make a similar move against NATO, what is the evidence that a SLCM-N would cause him to change his calculation? If such evidence exists, can NATO afford to wait until the 2030s to close this deterrence gap as opposed to taking more immediate action (like bolstering eastward conventional forces)?

Regarding the growth of China’s nuclear arsenal, do STRATCOM and the Department of Defense believe that China would deploy fewer new nuclear weapon systems with ranges over 500 kilometers if the United States were building some number of SLCM-Ns? Recent trends suggests that China is more likely to respond to the development of SLCM-Ns by deploying additional capabilities that threaten U.S. and allied interests. If so, how does the arms race stop?

Regarding Richard’s requirement of “low-yield, non-ballistic capability,” the long-range stand-off weapon (LRSO) is scheduled to be deployable around 2030 on B-52 and then on B-21 bombers. The LRSO and SLCM-N are likely to have almost identical military characteristics in terms of their flight paths after launch and warheads whose explosive power can be dialed up or down. Advocacy for the SLCM-N, therefore, seems to imply a concern about whether the planes meant to carry the LRSO could reliably avoid being destroyed before they launched their weapons. But, if that is so, why not pursue the SLCM-N instead of the Air Force’s expensive B-21 bomber and nuclear-armed cruise missile programs? Or, wiser still, why not focus the Air Force and STRATCOM on deploying the bomber and cruise missiles in ways that make them extremely survivable, obviating the claimed need for the SLCM-N?

In cases where invisible, low-yield nuclear weapons that can penetrate adversary missile defenses would be necessary, the newly deployed, low-yield W76-2 warhead on submarine-launched ballistic missiles could likely serve this purpose.

What Are Potential Operational Trade-offs or Risks in Building and Deploying the SLCM-N?

Risks and trade-offs would differ somewhat depending on whether nuclear-armed SLCMs would be deployed only on attack submarines or also on surface ships. Given Richard’s emphasis on the value of invisible generation, it appears that the proposed SLCM-N would be deployed on submarines. This surmise should be clarified. 

Several potential trade-offs stand out:

  • The presence of nuclear-armed missiles could require burdensome additional measures to ensure personnel reliability, training, and operational security of these submarines and their crews.
  • The presence of nuclear-armed missiles could affect the availability of these submarines for conventional war-fighting missions, reducing their effectiveness in conventional deterrence and warfighting, especially against China.
  • If a U.S. nuclear-armed submarine were attacked in a conventional war—regardless of whether Chinese or Russian attackers knew that SLCM-Ns were aboard—then U.S. leaders, including in Congress, might react in ways more likely to escalate the conflict than they would if a non-nuclear-armed vessel were hit, whether prudent or not.
  • The U.S. Navy hopes to build thirty-eight Virginia-class attack submarines, each of which could launch up to sixteen SLCM-Ns. If a large number of SLCM-Ns are to be deployed, there would be a real cost in terms of a significant reduction in the availability of conventional cruise missiles (or else an expensive call to build more submarines to carry, say, hundreds of SLCM-Ns). If the number is small, it raises questions about the value of a redundant program costing many billions of dollars.

What Are Potential Alliance Management Trade-offs and Risks?

Returning to Richard’s suggestion that the SLCM-N is necessary to bolster U.S. assurance of allies, what would NATO allies have done, or what would they do differently in the future, vis-à-vis Russia and Ukraine if the United States had deployed SLCM-Ns? Which allies are not being resolute and are not contributing to NATO objectives now but would behave differently if there were SLCM-Ns?

Regarding assurance in Asia, allies always want more, but they also do not want to trade off conventional naval warfighting capabilities for a marginal increase in nuclear capabilities. The key, historically, has been that allies perceive that the United States is deploying weapons that could credibly be used in ways that could keep nuclear war limited. If deploying some number of nuclear-armed SLCMs would significantly reduce the conventional warfighting capabilities of the U.S. nuclear submarine force, which Asian allies would prefer that to relying on the LRSO, B61s, and W76-2s for limited nuclear warfighting?

One argument for SLCM-Ns is that they would free the United States from relying on the five NATO allies that currently host and prepare to deliver B61 bombs. Yet, each of the five NATO nuclear-basing states remains committed to continuing this role. Allied solidarity has intensified with Russia’s invasion of Ukraine. This would seem to diminish the perceived need to turn to submarines to solve an allied basing problem in Europe.

In Asia, historically, port visits by U.S. vessels carrying nuclear weapons have been controversial. Moreover, the joint Australia, UK, and U.S. strategic initiative known as AUKUS centers around cooperative building and deployment of attack submarines that do not carry nuclear weapons, in keeping with Australia’s firm commitments under the Nuclear Non-Proliferation Treaty. Are U.S. President Joe Biden’s officials wrong to be concerned that nuclearizing SLCMs on attack submarines would create a political wedge that various opponents could exploit in Australia, Japan, and international bodies?

What Are Potential Arms Control Trade-offs and Risks?

Former U.S. president Donald Trump’s administration argued in 2018 that SLCM-Ns should be developed to catalyze arms control. But deploying SLCM-Ns would impede the negotiation of verifiable arms control with Russia and/or China when the strategic and political environments improve. Moscow or Beijing might bargain to limit or reduce their own nuclear forces to induce the United States to forgo SLCM-Ns, but there is no evidence for this sunny scenario. And if the United States deployed any of these weapons, its navy would likely be unwilling to allow Russian, Chinese, or other inspectors onto submarines to verify their number and/or locations. This would preclude future arms control treaties because the U.S. Senate would not ratify them without onsite verification.

Knowledgeable insiders suggest the cost of an SLCM-N program and its related nuclear warheads would be in the tens of billions of dollars, though budgets have not been presented or analyzed. How many weapons would budget planners be told to assume building? If a new warhead is to be included, how plausibly would it be available at the same time as the SLCM-N in the early 2030s, and at what cost, given how challenged the National Nuclear Security Administration is in meeting existing obligations? What changes (and at what cost) would need to be made in securing and otherwise modifying ports and other facilities that have not handled nuclear weapons in recent decades?

Given the trade-offs discussed earlier and the existence of three other low-yield nuclear weapon systems in the pending U.S. arsenal, it seems clear that these funds could be spent more effectively on other defense needs, domestic needs, or deficit reduction.

Champions of the SLCM-N will mobilize, especially on Capitol Hill, but their assertions and claims should be subjected to the kind of careful examination that informed the Biden administration’s Nuclear Posture Review decision not to spend untold billions on this unnecessary nuclear weapon.