An unarmed Trident II D5 missile launches from the Ohio-class ballistic missile submarine USS Nebraska (SSBN 739) off the coast of California. Photo Credit: U.S. Navy/Mass Communication Specialist 1st Class Ronald Gutridge.
In the 2018 Nuclear Posture Review, the Trump administration announced its plan to develop two new low-yield nuclear weapons, including a low-yield warhead for the Trident D-5 submarine-launched ballistic missile (SLBM) and a sea-launched cruise missile (SLCM). This development comes in response to concerns that the US suffers from a tactical ‘gap’ in its nuclear arsenal, which could lend states like Russia a unique coercive advantage in regional conflicts.
The new low-yield nuclear warhead, the W76-2, was successfully deployed in January on the USS Tennessee. Although the administration and some US experts assert the weapons will counter nuclear coercion, enhance the credibility of the American deterrent, and assuage allies’ fears that the U.S. would abandon them in the event of a limited nuclear conflict, expanding the United States’s tactical nuclear arsenal could have destabilizing and costly implications.
As tensions between great powers rise, there is just one surviving bilateral arms control agreement limiting US and Russian nuclear forces (New START). Even so, experts increasingly doubt whether the Trump administration will extend the Obama-era agreement. The result is an increasingly unstable and unregulated nuclear landscape. Under these conditions, the U.S. must exercise strategic restraint when it comes to expanding its nuclear arsenal and avoid tit-for-tat measures that may lower the nuclear threshold, trigger new arms races, and increase first-strike instability. History certainly cautions against such behavior.
The Argument for Expanding the United States’s Low-Yield Nuclear Arsenal
Advocates for expanding the American low-yield nuclear arsenal point to our adversaries—namely, Russia and, to a lesser extent, North Korea—to highlight an alleged ‘gap’ in the U.S.’s nuclear deterrent capabilities.
Some contend that if Russia were failing in a conventional conflict against NATO, it would launch a limited strike with a low-yield nuclear weapon to compensate for its conventional inferiority, thereby coercing NATO to withdraw. In this case, the U.S. would arguably only have the option of retaliating with a higher-yield weapon, making the response disproportionate. This asymmetry may inhibit the U.S. from responding to the Russians at the outset of nuclear escalation. Though widely contested, some believe this is part of Russia’s ‘escalate-to-deescalate’ strategy—leveraging calculated escalation to contain conflict at lower levels to achieve desired ends. Deploying a similar, low-yield nuclear weapon would, according to advocates, bolster the U.S.’s deterrence posture by increasing Russia’s perception that the US may be more inclined to use a limited nuclear option, therefore strengthening the credibility of the U.S.’s deterrent.
Of similar concern is North Korea. A handful of scenarios exist wherein Pyongyang may attempt to coerce the United States by launching—or threatening to launch—a limited nuclear first strike against a US regional ally, recognizing that the U.S. is not positioned to deliver a proportionate nuclear response. This could occur if North Korea perceives an imminent attack on the regime, or if a conventional conflict erupts on the Korean Peninsula and Pyongyang is hindered by its conventional inferiority.
In both scenarios, Moscow and Pyongyang would be challenging the credibility of the United States’s extended deterrent. Would Washington use a higher yield nuclear weapon to defend its allies in response to a limited nuclear strike? Naturally, this question causes US allies concern. W76-2 advocates maintain that the weapon enhances Washington’s ‘flexible’ and ‘tailored’ response options and therefore strengthens the credibility of the American deterrent. This thinking traces its roots back to John F. Kennedy’s “Flexible Response” strategy, which posited that the U.S. must maintain a range of options for responding to crises, ensuring that each action undertaken by an adversary can be met with a proportional response. Kennedy’s “Flexible Response” strategy, though intended to strengthen deterrence and strategic stability, had the opposite effect in practice. Indeed, efforts to match the Soviet Union at each level of the nuclear escalation ladder triggered instability and a costly arms race.
With the lessons of history behind us, the U.S. must exercise prudence in responding to potential threats, particularly when it comes to modernizing and expanding the US nuclear arsenal. Currently, US nuclear modernization plans prescribe an unsustainable approach to maintaining an effective and credible deterrent.
Why Deploying More Low-Yield Tactical Nuclear Weapons is Destabilizing
Deploying more low-yield nuclear weapons is destabilizing because it may lower the nuclear threshold, trigger a costly and unnecessary arms race, and aggravate first-strike instability.
1. Lowering the Nuclear Threshold
The “nuclear threshold” refers to the point in a conflict where nuclear weapons would be used. By deploying the W76-2, Washington tacitly exhibited a lack of confidence in its willingness to use its existing nuclear weapons (primarily those with a higher yield) in response to a nuclear attack. In other words, by adopting low-yield nuclear weapons, the US is signaling that it may be self-deterred from using its current conventional or nuclear forces. The implication, therefore, is that by deploying weapons with a smaller yield, the US may be more likely to use them in a conflict. Introducing more ‘usable’ low-yield nuclear weapons—or increasing perceptions that the U.S. may be more inclined to launch a limited nuclear strike—risks lowering the nuclear threshold. This is troubling for a number of reasons.
First, Russia’s ‘escalate-to-deescalate’ strategy—the primary threat the U.S. is responding to with the new W76-2 and SLCM—is highly disputed. Some contend the U.S. has conflated the development of Russia’s tactical nuclear arsenal with Moscow’s increased willingness to use tactical nuclear weapons in a regional conflict. The Kremlin has repeatedly rejected assertions that Russia maintains an ‘escalate-to-deescalate’ strategy, particularly in the nuclear realm. This begs the question: What if we’re wrong about Russia’s strategy? While it’s impossible to ascertain what the Kremlin’s true intentions are, by deploying the W76-2 and expanding our low-yield nuclear arsenal, Washington has signaled to Russia (and the world) that the U.S. has new nuclear capabilities it may be more willing to use. Russia will inevitably perceive these deployments as a threat, and may, in turn, harden their nuclear policies and reinforce their tactical nuclear capabilities in response. The consequence: rising tensions and uncertainty over intent, coupled with more provocative nuclear force postures on both sides. Granted, the U.S. could mitigate some of these challenges by refining its declaratory policy, perhaps specifying that it would only consider using the new low-yield weapons in response to a nuclear strike against the US or its allies. This would, at least, affirm that the US does not intend to use its limited nuclear capabilities to launch a first strike.
Second, enhancing the U.S.’s ability to respond in kind to a limited nuclear strike carried out by the Russians may actually increase, rather than contain, the risk of nuclear escalation. Here, the question becomes: Would the Russians withdraw after a limited US retaliatory strike? If the answer is no, then our low-yield nuclear capabilities offer little utility for deterrence.
Third, and perhaps most importantly, the notion that lower-yield nuclear weapons are more credible because the U.S. may be more likely to use them risks obscuring the fact that a nuclear weapon is still a nuclear weapon. The use of any nuclear weapon in a conflict, regardless of the yield, would shatter critical norms that have developed over decades, and would trigger chaos, global condemnation, and mass destruction. That is, after all, the function of a weapon of mass destruction. The U.S. must not lose sight of the fact that nuclear weapons should remain an option of last resort.Deploying more weapons of a lower yield threatens to undermine this principle by implying that the weapons themselves are more ‘usable,’ and because of their low yield, somehow more morally tenable.
2. Intensifying Arms Race Pressures
In addition to lowering the nuclear threshold, the decision to deploy more low-yield nuclear weapons may intensify arms race pressures. Bolstering the U.S.’s low-yield nuclear arsenal legitimizes the notion of ‘nuclear parity’—that the country’s current nuclear capabilities must match the Russians in order to counter nuclear coercion and enhance stability. This Cold War-era thinking is detrimental because it fails to recognize that not all nuclear asymmetries are inherently destabilizing. The U.S. should thus resist succumbing to arms race pressures for three key reasons.
First, the US can counter Russian aggression with its existing capabilities—even if the Russians launched a limited nuclear strike in a regional conflict. The U.S. has an unprecedented conventional advantage and a robust nuclear triad. Not to mention, the U.S. already has approximately 1,000 low-yield nuclear weapons in its arsenal, including the highly accurate, dial yield B-61. The B-61 has a Circular Error Probability (CEP) of just 30 meters—meaning, 50% or more of the weapons launched would land within a 30 meter radius of the target. This is compared to the U.S.’s other nuclear weapons, which have a CEP of 110-170 meters. Moreover, the B-61 has a maximum yield of 50 kilotons, but the weapon’s dial-a-yield system can reduce its explosive force, making the B-61 an attractive low-yield option. The U.S.’s existing capabilities suggest that the supposed need to deploy more low-yield nuclear weapons to fill a tactical ‘gap’ is, from a force posture perspective, overstated.
Second, arms races are costly—especially when the U.S. already has sufficient means to respond to its adversaries. Third, arms races undermine the American commitment to nuclear disarmament. Under the terms of the Treaty on the Non-Proliferation of Nuclear Weapons, the U.S. and its nuclear peers pledge to work toward eventual nuclear disarmament. The U.S.’s expansion of its nuclear arsenal to include more low-yield weapons contradicts this agreement and may encourage broader non-compliance among NPT signatories. If the U.S. is indeed committed to nuclear non-proliferation and disarmament, it should leverage its position as a global leader to demonstrate restraint when it comes to expanding its nuclear force posture. This would help reinforce the crucial tenets of the NPT and legitimize the U.S.’s role as a leader in nuclear non-proliferation and disarmament.
In short, rather than expending resources on new tactical weapons to facilitate nuclear symmetry—a step that is unnecessary and unsustainable—the U.S. should instead express full confidence in its existing capabilities, reaffirming its commitment to employ said capabilities in the event of an attack against the US or its allies.
3. Aggravating First-Strike Instability
While the U.S. may regard deploying more low-yield nuclear weapons as a stabilizing measure, its adversaries may not. Perceptions of ‘stability’ are indeed highly subjective. The U.S. must recognize that deploying low-yield nuclear weapons may exacerbate adversaries’ insecurities, especially when the adversary is conventionally inferior. This may, in turn, generate first-strike instability—when one side feels pressured by the force posture of the other to strike first, believing that striking first would be more advantageous than waiting. The risk of aggravating first-strike instability by deploying low-yield nuclear weapons is particularly acute in the Korean Peninsula, where North Korea is already sensitive to changes in the American force posture and US bilateral defense cooperation with South Korea and Japan.
For years, the North Korean regime has condemned joint military exercises carried out by the U.S. and its regional allies, especially those involving nuclear-armed B-52s, as blatantly provocative. Amid escalating tensions between the U.S. and North Korea in 2018, officials in Seoul called for the U.S. to remove nuclear-capable B-52 bombers from a planned exercise to avoid exacerbating tensions between the two parties.
Indeed, deploying low-yield weapons to the region may compound instability. Pyongyang may misinterpret the regional deployment of low-yield weapons as yet another signal that the U.S. is preparing to launch a nuclear first strike to eliminate North Korea’s leadership, its nuclear facilities, or its military infrastructure—especially if Pyongyang is operating under the assumption that the U.S. would be more willing to use a low-yield nuclear weapon to achieve its goals. Under these conditions, North Korea may perceive delivering a first strike as the best option for preserving its vital interests.
Again, the U.S. could refine its declaratory policy in an attempt to assure Pyongyang that regionally deployed low-yield weapons would not be used to deliver a first strike against the regime. But even that step is unlikely to meaningfully reduce tensions and mitigate fears given the pervasive distrust and conventional asymmetries between the two states.
In short, even if the U.S. enhances its tactical nuclear force posture around North Korea with the intent to strengthen its extended deterrent and counter nuclear coercion, Pyongyang may believe that the U.S. is preparing to launch a nuclear first strike against the regime. This may encourage, rather than deter, North Korea’s drive to strike first. The result is an increasingly unstable and dangerous regional landscape.
As the U.S. moves forward with developing and deploying the new SLBM nuclear warhead and SLCM, Washington must recognize and anticipate the challenges that may arise as a consequence. Given the potentially destabilizing implications outlined above, the U.S. must strive to minimize opportunities for misperception, accidents, and escalation. To this end, the U.S. should: 1) focus on crafting policies that leverage its existing conventional superiority to achieve desired ends; 2) shift to a ‘no first use’ declaratory policy which states that the U.S. will only consider using a nuclear weapon in response to a nuclear attack against the U.S. or a US ally; and 3) consistently and vigorously affirm its commitment to allies, reiterating that any action undertaken by an adversary against an ally will be met with a response from the U.S.
Formulating sound strategy requires that states identify their vital interests and critically assess effective ways for upholding those interests. Throughout this process, states must also account for adversaries’ perceptions, weigh potential costs, and have the courage to challenge existing trends and assumptions. As the global leader, the U.S. is uniquely positioned to set a precedent of restraint through its nuclear strategy and strengthen the foundation for peace. The U.S. is also capable of fueling the flames of escalation, instability, and conflict. Given the stakes, American policymakers must recognize the potential consequences of the recent changes to the U.S.’s nuclear posture and take corrective steps to put the United States back on a track that reduces, rather than heightens, the risk of nuclear conflict. Because, at the end of the day, no one wins in a nuclear war—no matter the scale.
 “Nonstrategic Nuclear Weapons,” Congressional Research Service, September 6, 2019, 1. https://crsreports.congress.gov/product/pdf/IF/IF11143.
 Amy F. Woolf, “A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate,” Congressional Research Service, January 10, 2020, 1. https://crsreports.congress.gov/product/pdf/IF/IF11143.
 William M. Arkin and Hans M. Kristensen, “US Deploys New Low-Yield Nuclear Submarine Warhead,” Federation of American Scientists, January 29, 2020.https://fas.org/blogs/security/2020/01/w76-2deployed/.
 Steven Pifer, “Extending New START is a no-brainer—and yet, we can’t count on it,” Brookings, February 20, 2019. https://www.brookings.edu/blog/order-from-chaos/2019/02/20/extending-new-start-is-a-no-brainer-and-yet-we-cant-count-on-it/.
 Woolf, “A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate,” 1.
 Arkin and Kristensen, “US Deploys New Low-Yield Nuclear Submarine Warhead” and Woolf, “A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate,” 1.
 Jay Ross, “Time to Terminate Escalate to De-Escalate—It’s Escalation Control,” War on the Rocks, April 24, 2018. https://warontherocks.com/2018/04/time-to-terminate-escalate-to-de-escalateits-escalation-control/.
 Woolf, “A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate,” 1.
 “Flexible Response,” Nuclear Files – Project of the Nuclear Age Peace Foundation. http://www.nuclearfiles.org/menu/key-issues/nuclear-weapons/history/cold-war/strategy/strategy-flexible-response.htm.
 Ross, “Time to Terminate Escalate to De-Escalate—It’s Escalation Control.”
 Robert Burns, “US adds ‘low yield’ nuclear weapon to its submarine arsenal,” Associated Press, February 4, 2020. https://apnews.com/b910d5f4f2076d558416ae021b511517.
 Fred Kaplan, “The Senseless Danger of the Military’s New ‘Low-Yield’ Nuclear Warhead,” Slate, February 18, 2020. https://slate.com/news-and-politics/2020/02/low-yield-warhead-nuclear-weapons-navy-trident-submarines.html and Zachary Keck, “Why the B-61 Bomb is the Most Dangerous Nuclear Weapon in America’s Arsenal,” The National Interest, October 9, 2018. https://nationalinterest.org/blog/buzz/why-b-61-12-bomb-most-dangerous-nuclear-weapon-americas-arsenal-32976.
Hans M. Kristensen, “B61-12: The New Guided Standoff Nuclear Bomb,” Federation of American Scientists, May 2, 2014, https://fas.org/programs/ssp/nukes/publications1/Brief2014_PREPCOM2.pdf.
 Keck, “Why the B-61 Bomb is the Most Dangerous Nuclear Weapon in America’s Arsenal.”
 Glenn A. Kent and David E. Thaler, “First-Strike Stability: A Methodology for Evaluate Strategic Forces,” RAND, R-3765-AF (August 1989), vi. https://www.rand.org/content/dam/rand/pubs/reports/2008/R3765.pdf.
 Michael R. Gordon and Nancy A. Youssef, “US Scrapped Training Exercise with South Korea Involving B-52s,” The Wall Street Journal, May 18, 2018. https://www.wsj.com/articles/u-s-scrapped-training-exercise-with-south-korea-involving-b-52s-1526651491.