The International Legal Environment for Nuclear Deterrence

Russian spy ships stationed off the U.S. coast, provocative overflights of U.S. warships, and deployments of U.S. tanks in Central Europe are no longer artifacts of the Cold War, they are troubling features of the current international security environment. Whether and to what extent recurrence of these incidents will resurrect Cold War political and military strategies is for now unclear. But the security calculus of major powers and their allies will surely involve new reviews of the nuclear strategies and capabilities that remain at the core of their national strategic deterrence. In fact, among the new U.S. administration’s flurry of initial directives was a Jan. 27 memorandum ordering the Defense Department to initiate a Nuclear Posture Review “to ensure that the United States nuclear deterrent is modern, robust, flexible, resilient, ready, and appropriately tailored to deter 21st Century threats and reassure our allies.”

Just one month earlier, the United Nations General Assembly passed a resolution to convene a March 27 conference in New York “to negotiate a legally binding instrument to prohibit nuclear weapons, leading towards their total elimination[.]” In addition to backing from the 113 Member States which voted in favor of the resolution, the effort has support from influential non-State actors like the International Committee of the Red Cross and a host of Nobel Laureates.

Predictably, nuclear-armed States and their allies oppose the resolution and the conference. A joint statement by the United States, the United Kingdom, and France argued a new convention would undermine the existing, consensus-based 1968 Treaty on Non-Proliferation of Nuclear Weapons (NPT). Interestingly, China and India, both acknowledged as nuclear-armed States, merely abstained on the resolution and even recently attended an organizing meeting that produced a draft agenda for the conference. Some have already concluded the anticipated treaty between the member states who voted for the conference will outlaw nuclear weapons per se.

Of course, no agreement between select States can produce such ban. Only a universally-ratified treaty or an airtight rule of customary international law could do this. The most likely outcome of the conference will be a nuclear-weapon ban applicable to select, ratifying States, in addition to the obligations non-nuclear States already bear under the NPT. 

Still, nuclear-armed States and others that do not participate in the conference may encounter legal and political pressure as a result of the new convention. Indeed, at the organizing meeting for the conference, Ireland argued that a goal of the process should be to make possession of nuclear weapons “less comfortable” for nuclear armed States. The conference, the convention, and the international attention they will garner will present an occasion for nuclear-armed States to evaluate their legal and strategic positions on nuclear weapons, including the extent to which the international legal environment supports deterrence strategies involving nuclear weapons.

Understandably, humanitarian suffering arising from the devastating effects of nuclear weapons is the chief concern behind efforts to outlaw nuclear weapons. Advocates of a nuclear weapon ban have long argued that they cannot be used consistently with the law of war under any circumstances. But efforts to define the precise relationship between international law and nuclear weapon use have ended with inconclusive results.

Modern analysis usually begins with a 1996 advisory opinion from the International Court of Justice after it was called on to evaluate whether the threat or use of nuclear weapons could ever be lawful. The deeply divided Court equivocated, concluding the answer was unclear—a legal non liquet. While the Court confirmed that “cardinal principles” of the law of war such as the principle of distinction between civilians and military objectives and combatants apply to nuclear weapons use, it declined to provide any specific doctrine or guidance.

The Court’s ambiguity with respect to how the law of war operates in nuclear targeting judgments mirrors State legal doctrine. Nuclear-armed States have issued only vague legal doctrines on nuclear weapon use. President Obama’s guidance was to “apply the principles of distinction and proportionality and seek to minimize collateral damage to civilian populations and civilian objects.” The U.S. Department of Defense Law of War Manual states, the “law of war governs the use of nuclear weapons, just as it governs the use of conventional weapons.”  It further explains that they must be directed against legitimate military objectives and be used proportionately. But the extent to which the full panoply of U.S. targeting doctrine and policies apply to nuclear weapons is unclear from publicly-available sources. The United Kingdom’s Joint Service Manual of the Law of Armed Conflict explains that nuclear weapon use is governed by reference to the same general principles as apply to other weapons; however, new rules introduced by the 1977 Additional Protocol to the Geneva conventions do not regulate or prohibit their use.  The French manual is even more circumspect, only admitting that nuclear weapons are subject to the law of armed conflict, with its limitations on means and methods of warfare and prohibitions on weapons with indiscriminate effects and which cause unnecessary suffering or superfluous injury.

Opposition to nuclear weapons is not based exclusively on legal considerations. Advocates of a nuclear ban have extended their arguments to major premises of nuclear deterrence. Austrian Ambassador Alexander Kmett rejected the continuing utility of these weapons, writing, “the concepts of nuclear deterrence and the necessity of nuclear strategic stability, which were merely transferred to the 21st century with little change, look increasingly anachronistic 20 years after the end of the Cold War.” Mexico’s foreign minister similarly rejected the international security justification for the weapons.  Meanwhile, advocacy groups in the U.S. and allied nations repeat these themes and threaten to undermine political support for nuclear deterrence.

Despite these arguments, the current relationship between nuclear weapons and nuclear-armed States’ national security strategies is quite clear. U.S. nuclear strategies and capabilities have been in periodic evolution since the end of the Cold War.  Dr. Brad Roberts, policy director of the Obama administration’s Nuclear Posture Review, argues nuclear weapons remain essential for interrelated deterrence efforts to dissuade aggression, assure allies, maintain a strategic balance, and enable the U.S. to manage the risks associated with its national strategy of international engagement and power projection. However, the application of deterrence theory is notoriously complicated with various theories about how to maintain it presenting seemingly endless branches and sequels (See, e.g., here, here, here, here, here, here, here, and here).  Common to most theories is the importance of credibility. To deter an adversary, a power must credibly threaten the consequences it thinks will achieve deterrence. In a nuclear context, a State’s threat to use nuclear weapons in response to aggression must be credible to be effective.

International law especially plays an under-appreciated role in deterrence. Credibility is not simply a matter of capabilities or demonstrating resolve and willpower; it is also based on a nation’s cultural, moral, and legal values. A nation self-identifying as a champion of the rule of law and of international legal rights and obligations would have a difficult time making a believable case for deterrence by threatening patently illegal action. Law-abiding States committed to nuclear deterrence as a means to international stability must maintain the position that nuclear weapon use is ultimately permitted by the law of war, or their deterrence policies will forsake credibility.

Thus, nuclear States should respond proactively to the upcoming nuclear treaty conference. A helpful step would be to further clarify the legal parameters of nuclear weapon use. But in doing so, nuclear-armed States should be mindful of where ambiguity supports deterrence, and where it unnecessarily ignores public concerns.

In some cases, ambiguity associated with the way States apply the law of war to nuclear targeting may be warranted. For instance, the requirement that attacks not result in collateral civilian damage and casualties that are excessive in relation to military advantage—the rule of proportionality—is generally acknowledged to apply to nuclear weapon use. Yet the precise ratio that is acceptable between unintended collateral damage and desired military advantage is entirely unclear. Similarly, exactly how nuclear-armed States would value military advantage in a nuclear strike has not been explained. Although States have a clear obligation to avoid civilian casualties, they also have an interest in maintaining ambiguity as to the application of proportionality to prevent adversaries from benefitting from bad faith maneuvers such as mixing military assets among protected people and objects.

In other areas, ambiguity may be less advantageous. For instance, many misgivings about nuclear weapons involve the potential targeting of population centers. The United States has long maintained that it does not target civilian populations or civilian objects. But concepts such as “Mutually Assured Destruction” and counter recovery targeting surely provoke skepticism.  Scott Sagan and Jeffrey Lewis have written that a solution may be to reintroduce the principle of military necessity into employment guidance. While their proposed rule to “never use nuclear weapons when conventional weapons could destroy the target”is debatable, their overall goal is to encourage strict application of the laws of war and to assure our public and our allies that the principles of the laws of war are at the heart of our deterrence and security policies.

Finally, nuclear-armed States might evaluate their reliance on the doctrine of belligerent reprisal. Belligerent reprisal doctrine permits States involved in armed conflict to reply to enemy law of war violations with actions that would otherwise be law of war violations. It is a controversial doctrine that twentieth-century laws of war sought to eliminate or significantly narrow through limitations. Most notably, Additional Protocol I to the 1949 Geneva Conventions limited reprisals to military targets. It is likely not a matter of coincidence that nuclear-armed States resolutely resisted elimination of reprisal and lodged reservations. Reprisal offers an enticing justification for aggressive nuclear planning. The extent of targets available in a reprisal scenario is limited only by the imagined extent of enemy depravity. It is unclear the extent to which publicly-stated disavowals of reprisal would undermine deterrence credibility. But a careful accounting of both the operational benefits and public legitimacy costs of preserving reprisal doctrine is surely warranted.

As part of the 2017 Nuclear Posture Review, the U.S. should evaluate its legal position on the use of nuclear weapons. Most importantly, the Review should state, as clearly as deterrence goals permit, the U.S. position on the relationship between international law and nuclear weapon use, to include the U.S. position on the threat or use of such weapons as a lawful belligerent reprisal. Where possible, such a review should seek to mitigate humanitarian concerns and reassure allied populations with clear legal guidance. Where clarity would too greatly compromise deterrence and credibility, the Review should actively preserve ambiguities, especially the extent to which precision would provide advantages to an adversary.

Such clarifications, whether in the form of refined legal doctrine or simply confirmations of ambiguity, would serve two important functions. First, such work would better guide those assigned to ensure nuclear plans comply with the law of war. Second, this work would secure the U.S. role in crafting the international law environment for nuclear weapons. Active management of this legal environment, whatever the prevailing domestic political reality, will both serve U.S. security interests and restore the pluralistic balance of sovereign and humanitarian interests critical to effective international lawmaking.

The views expressed in this post are solely those of the authors and do not reflect the official policy or position of the DoD or the U.S. Government.

Image: U.S. Navy. 

About the Author(s)

Lt. Col. Ted Richard

Judge Advocate in the United States Air Force and Deputy Staff Judge Advocate at U.S. Strategic Command

Sean Watts

Professor at Creighton University Law School, Reserve Instructor in the Department of Law at the United States Military Academy at West Point, Senior Fellow at the NATO Cooperative Cyber Defence Centre of Excellence, Served as an Active-Duty Army Officer in both the Armor and Judge Advocate General’s Corps (1992-2007), Current Army Reservist