war on the rocks

Addressing Fears About the Nuclear Posture Review and Limited Nuclear Use

February 28, 2018

Would the launch of a single Trident II missile cause the submarine that fired it to be detected and sunk, trigger a massive nuclear exchange, or both? If you believe the critics of the 2018 Nuclear Posture Review, that’s exactly what would happen. In addition, these critics charge that even the review’s proposal to modify some Trident II warheads to carry a lower yield will make nuclear war more likely. However, a solid array of facts undercuts each of the critics’ charges and sustains the Nuclear Posture Review’s (for which I served as a senior advisor) case that deploying modified Trident warheads actually strengthens deterrence.

Why Does the United States Need a Low-Yield Warhead on Submarine-Launched Missiles?

Western governments believe that over the past 10 to 15 years the Russian military has placed increasing emphasis on the use of low-yield nuclear warheads to blunt NATO’s ability to defend its territory, particularly the Baltic states, against Russian military attack.

Ashton Carter, then secretary of defense under the Obama administration, similarly observed in 2016:

[I]t is a sobering fact that the most likely use of nuclear weapons is not the massive nuclear exchange of the classic Cold War type but rather the unwise resort to smaller but still unprecedentedly terrible attacks, for example by Russia … to try to coerce a conventionally superior opponent to back off or abandon an ally during a crisis.

Carter’s concern was based on three factors. First, Russian military doctrine, since the 1990s, has included the use of lower-yield nuclear weapons to defeat enemy conventional forces (i.e. US/NATO) on the battlefield. Second, to support this, Russia retained tactical nuclear systems it had pledged to destroy; in the last decade, it has also fielded new nuclear tactical ballistic missiles. Third, the Russians have exercised using nuclear weapons in this manner.

It is particularly worrisome that Russia pursued these developments in the face of the obvious capabilities of the U.S. strategic triad and of America’s Europe-based dual-capable aircraft. Because the Russian military is anything but frivolous, we must conclude that its leadership believes that despite the capabilities of America’s current nuclear deterrent, the United States lacks a credible option to respond to Russian use of tactical low-yield weapons on the battlefield to win a war.

Several decades ago, former Secretary of Defense Caspar Weinberger noted, “Deterrence is a dynamic effort, not a static one. In order to continue to deter successfully, our capabilities must change as the threat changes and as our knowledge of what is necessary to deter improves.” The 2018 Nuclear Posture Review echoes this verity: “Potential adversaries do not stand still. On the contrary, they seek to identify and exploit weaknesses in U.S. capabilities and strategy. Thus, US future force requirements for deterrence cannot be considered fixed.” This is a key point: The United States seeks to prevent attacks against ourselves and our allies. If political leaderships of potential adversary nations understand that initiating aggression will result not in victory, but rather in a situation that could threaten their national existence, war is prevented. On the other hand, if potential enemy military commanders can convince their political leaders that nuclear use can both be confined to the battlefield and result in victory, then peace is at risk.

Accordingly, after a full review of both Russian developments and existing U.S. capabilities, the Nuclear Posture Review concluded that a new capability was required to ensure

the Russian leadership does not miscalculate regarding the consequences of limited nuclear first use … Russia must instead understand that nuclear first use, however limited, will fail to achieve its objectives, fundamentally alter the nature of a conflict, and trigger incalculable and intolerable costs for Moscow.

As a result, the review recommended modifying a small number of W-76 Trident II warheads to underscore the seriousness of this policy and strengthen Russian perceptions of U.S. credibility and will. These modifications can be accomplished relatively inexpensively, in a short amount of time, and without adding additional weapons to the stockpile.

The choice of modified Trident II warheads clearly indicates that the United States would not respond in the theater or on the battlefield, but rather strike back against targets of significance to the Russian leadership. Contrary to what critics have written, deploying these warheads will therefore raise, not lower, the nuclear threshold, making aggression and nuclear weapons employment less likely.

Some academics have written that they do not consider the Russian developments to be a real threat. However, policymakers and scholars must necessarily approach these questions in different ways. As Robert Jervis observed of an earlier divergence between policymakers and academics over nuclear strategy:

I think the reason is that people in positions of power feel a great sense of responsibility that academics cannot share. They need to face the question of what they would do in the event of a conflict … Academics could argue that the Soviets were not strongly motivated to attack or that, even if they were, the bargaining advantage lay with the defender … But those who had to think about what they would do if a terrible situation arose could not be satisfied by those responses.

In this case, the majority of Western intelligence agencies and governments disagree with the academics’ analysis, and believe that the Russian military has advanced a military doctrine that features the use of nuclear weapons, deployed weapons systems to support that doctrine, and exercised the use of those weapons systems to drive the point home. If one occupies a position in the U.S. government and is responsible for national security, one cannot ignore these facts.

Would the Launch of One or Two Trident Missiles Risk the Submarine’s Survivability?

A point raised consistently by critics of a low-yield submarine-launched ballistic missile (SLBM) warhead is that the launch of a single Trident missile will cause the submarine that fired it to be detected by an enemy and sunk. This assertion is wrong on two points: First, it misrepresents longstanding U.S. nuclear policy and, second, it downplays how difficult it is for adversaries to detect and attack American submarines.

To begin with, this line of criticism assumes that the launch of a single missile (or even a few missiles) is unthinkable, i.e., that U.S. missile submarines would only launch all of their missiles at once. For over 40 years, however, U.S. nuclear deterrent plans have included multiple so-called “small options,” that is, retaliatory options that only employ a handful of missiles, designed with the hope that they could be used to control escalation. It would be reasonable to assume that plans assigned to U.S. ballistic missile submarines, or SSBNs, include those small options. As a result, because the concept of “spasm war” — in which both sides launch all their weapons at the other — became incredible in the 1960s, it is also reasonable to assume that for decades the United States has envisioned the possibility of so-called “split launches,” in which the SSBNs fire only a small number of missiles if so ordered. This means that the Department of Defense has full confidence that the submarine will remain fully survivable even after launching only a portion of the missiles it carries.

With regard to the anti-submarine problem — which involves using existing technologies to find and sink the SSBN which fired the missile — we should stipulate up front that the U.S. submarine is not being “trailed” by an enemy submarine. If it were, the mission would have been compromised already. However, U.S. SSBNs are designed and operated in such a manner that enemy trail is virtually impossible. Second, we should stipulate that the oceans have not become transparent nor are they likely to do so in the foreseeable future. While some today claim advances in drone or other technology will in the not too distant future effectively make the oceans transparent, similar possible technological breakthroughs have been discussed since I was an ensign in the Navy in the early 1970s but have yet to come to fruition.

Now assume, unreasonably but for the sake of argument, that a potential adversary has space-based infrared sensors that can immediately geo-locate the exact position of the American SSBN launching one or several missiles; and that said sensors’ information can be instantly relayed to a command center which will re-program an ICBM to attack that point in the ocean. In the 20 minutes or so which will have elapsed before the ICBM brackets that point, the U.S. submarine, traveling at 20 knots, can move over 6 miles in any direction, yielding a circular field of uncertainty of over 137 square miles. That’s a tremendous amount of ocean for the adversary to attack. Note as well that the destructive power of nuclear weapons, even if they were able to survive water entry after a 20-minute ICBM flight, is attenuated severely by water; the physics of nuclear weapons exploding underwater was studied exhaustively during the Cold War. Dozens of reentry vehicles — and therefore, many ICBMs — would be needed to carry out an attack with any chance of success. If, however, multiple ICBMs had to be re-targeted, adding, say, another 10 minutes to the process, the area of uncertainty would expand to 314 square miles, requiring hundreds of reentry vehicles. This scenario is simply not credible. Even after launching a single missile carrying a low-yield warhead, the U.S. submarine is survivable.

Would Russia Interpret the Launch of One or Two Missiles as the Start of a Nuclear Attack?

Especially during a crisis or conflict, U.S. and Russian decision-makers take the entire threat environment into account — not simply one action. Just as U.S. officials would not automatically be expected to respond to limited Russian nuclear employment with a massive response, they should not expect Russia to do so either. The logic supporting this argument has been clear for decades: The costs of a massive response far outweigh the benefits. Moreover, Russian intelligence collection capabilities, as well as U.S. and allied messaging, would reinforce the limited nature of the nuclear employment.

To be sure, once a nuclear weapon has been used nothing is certain. That fact alone enhances deterrence, because the aggressor government cannot have total confidence that the war could be contained and halted short of mutual annihilation. But both U.S. and Russian nuclear plans have, for decades, discounted the notion that any nuclear use, including the launch of one or a handful of ballistic missiles, will lead immediately to a “spasm war.” Beginning with the Kennedy administration’s introduction of the “flexible response” strategy in the early 1960s, further refined by Secretary of Defense James Schlesinger in the mid-1970s and his successors, limited or small options have been a feature of the U.S. strategic deterrent for a long time. Those options have been designed and tailored to be as discernable as possible by Russian early warning systems. Those who believe that the only type of nuclear war is an all-out spasm war will caricature this. But the fact is that U.S. policymakers have for decades embraced small options as a means of providing credible response options to deter limited nuclear attacks — and thereby to halt any attempts to attack the United States or its allies in the first place.

To conclude, the Nuclear Posture Review’s call for modest but important adjustments to U.S. nuclear forces is not a major departure from more than 50 years of U.S. nuclear strategy. It is responding to a plausible threat of Russian low-yield use of nuclear weapons, which has developed in the last 15 years despite current U.S. capabilities. The introduction of a lower-yield W76 warhead does not change U.S. nuclear policy, which long ago incorporated limited nuclear options to deter and, if necessary, respond to aggression.

Instead, in an era of renewed competition with Russia, and potential for conflict that the Russian military believes could include limited nuclear use, a small number of modified W76 warheads will fill any gap in U.S. deterrent capabilities that the Russians might perceive in a rapid and affordable manner. Filling this gap will raise — not lower — the nuclear threshold and reduce the chances of aggression. Finally, the launch of a single or a few missiles will not make a U.S. SSBN vulnerable to attack, nor will it signal the initiation of a massive U.S. strike. The Nuclear Posture Review’s plans rely on a rational assessment of the threat environment and U.S. and Russian commanders’ awareness of the gravity of launching an all-out attack. In this way, the proposals are consistent with decades of U.S. nuclear plans and the logic of deterrence.

CORRECTION: A previous version of this post stated that a U.S. SSBN, moving at 20 knots, can travel 13 miles. At that speed, the vessel can travel 6.6 miles. 

Franklin C. Miller is a retired senior civil servant. He spent two years at the State Department, twenty-two years in the Defense Department and four years on the White House staff.

Image: U.S. Navy/Amanda R. Gray