---

In the first half of 2023, a group of fellows from the Nuclear Risk Reduction Fellowship hosted by the Council on Strategic Risks sought to examine the value of unilateral declarations as risk reduction measures.¹ Specifically, they looked at how—and under what conditions—a state can unilaterally implement an effective risk reduction measure, and the potential benefits and drawbacks to acting alone.

Unilateral declarations are no substitute for legally binding bilateral and multilateral accords, but, in the absence of a political environment favorable to the negotiation of formal treaties and agreements, unilateral declarations offer an apt alternative to codifying new commitments.

In this respect, and considering the ongoing war in Ukraine as well as the end of nearly all arms control agreements between Russia and the United States, the fellows explored what it might look like for the North Atlantic Treaty Organization (NATO) to issue a unilateral declaration adopting a sole purpose doctrine for NATO nuclear forces. They considered how such a shift in NATO’s nuclear posture could lower the risk of nuclear use in Europe while pressuring Russia to make a similar commitment. They also assessed the potential drawbacks and added risks posed by this proposal, including the concerns such a change would likely raise among allies.

On June 30, 2023, the fellows led an interactive discussion with their cohort, Council on Strategic Risks staff, and former Deputy Secretary General of NATO and U.S. Under Secretary of State for Arms Control and International Security Rose Gottemoeller on the utility of unilateral declarations as risk reduction measures and the viability of a NATO sole purpose doctrine. The discussion was held under the Chatham House Rule. This briefer captures key ideas that emerged.

Historical Precedents of Unilateral Declarations as Risk Reduction Measures

A unilateral declaration is a statement made on behalf of a state ascribing it new rights or obligations. States have utilized this tool of diplomacy for centuries, spanning from the U.S. Declaration of Independence in 1776 to the security assurances granted to non-nuclear weapon states at the 1978 United Nations (UN) General Assembly Special Session on Disarmament.

Though issued unilaterally, a declaration pledging new, official rights and obligations for that state have the potential to significantly alter the international landscape. For instance, less than one year after U.S. Vice President Kamala Harris announced the U.S. commitment not to conduct destructive, direct-ascent anti-satellite (ASAT) missile testing in April 2022, a UN First Committee resolution upholding that same commitment was adopted by a 154-8 vote.² Later, at the UN General Assembly, the resolution was approved by 155 states.³ The resolution marked a historic feat for space security, and an important step toward the creation of a lasting international norm against ASAT testing.

Yet at the time VP Harris issued the U.S. unilateral declaration, the United States had not conducted an ASAT test in over a decade—not since 2008. Indeed, while the U.S. self-imposed moratorium on ASAT testing catalyzed global support and, for a handful of states, the adoption of similar moratoria, the initial U.S. commitment required no apparent change in policy or posture.

Similarly, although the George W. Bush administration submitted a proposal for a fissile material cut-off treaty (FMCT) at the Conference on Disarmament (CD) in 2006, the United States had not produced highly enriched uranium for weapons since 1964.⁴ The prospective treaty remains under deliberation in the CD.

A unilateral declaration can generate political progress toward a legally binding treaty or agreement, as may be the case for a future FMCT. This was also the case when U.S. President Richard Nixon’s November 1969 renunciation of the use of lethal biological agents and weapons created a pathway for the United States to support the United Kingdom’s draft convention to ban biological and toxin weapons. Prior to Nixon’s announcement, the United States had an offensive biological weapons program but had not used such weapons. Nixon’s declaration marked the first time a major power unilaterally abandoned an entire category of armaments and paved the way for the swift negotiation, adoption, and entry into force of the 1972 Biological and Toxin Weapons Convention (BWC).

Indeed, as evidenced by the 2022 ASAT resolution and the 1972 BWC, a state’s unilateral declaration to amend its policies or posture can be a valuable risk reduction tool when issued under certain circumstances. Chief among these benefits is the creation of a standing precedent by the issuing state of implementing the measures prescribed by the declaration—or, at least, a seemingly viable intention to uphold that commitment.

Legality of Unilateral Declarations

It is important to note that while there is no clear legal understanding of the difference between a unilateral declaration that is legally binding and one that is not, there is general consensus that a declaration made by an authority vested to do so (i.e., a head of state) could be considered binding under customary international law.

But this does not mean all unilateral declarations made by heads of state are binding. According to the UN International Law Commission’s Guiding Principles Applicable to Unilateral Declarations of States Capable of Creating Legal Obligations, “a unilateral declaration entails obligations for the formulating State only if it is stated in clear and specific terms. In the case of doubt as to the scope of the obligations resulting from such a declaration, such obligations must be interpreted in a restrictive manner.”⁵ Indeed, in Alfred P. Rubin’s The International Legal Effects of Unilateral Declarations, published in January 1977, he explains, “Whether a unilateral declaration should be regarded as binding is a question of the degree to which the international order needs to feel confidence in the continued effectiveness of the declaration; that in the absence of other indicators, this is a matter of context and subject to flexibility.”⁶

The prevailing position on the legality of unilateral declarations seems to suggest that a degree of ambiguity can protect the declarant state from the consequences of international law, should that state renege on its declaration. Flexibility can also offset the political challenges associated with a state’s internal decision to issue a unilateral declaration. Additionally, declarations made by a state (or states) on behalf of a larger organization or alliance may benefit from the ambiguity and flexibility inherent to a joint multilateral decision.

Benefits

In addition to the creation of a standing precedent, unilateral declarations can serve two other important purposes. First, they can act as a catalyst to motivate other states to adopt similar commitments. Most other risk reduction measures necessitate buy-in from multiple states, and thus struggle to generate political momentum or, in a worst-case scenario, risk being thwarted by a spoiler state. A first mover could help overcome this challenge by creating momentum and motivation for others to do the same. A state that already unofficially implements that risk-reducing measure is particularly well-poised to be that first mover, as issuing the unilateral declaration would simply formalize the measure it was already exercising without imposing substantial political or other types of costs.

Second, unilateral declarations offer an avenue for states to tacitly pressure their peers to respond in-kind by committing to new measures without formal negotiations toward a binding treaty or agreement. One such example is the Presidential Nuclear Initiatives (PNIs) on tactical nuclear weapons. This series of unilateral declarations began in September 1991 when then-President George H.W. Bush announced a trove of initiatives to limit and reduce the U.S. tactical nuclear weapons arsenal. These initiatives included withdrawing and destroying all U.S. ground-launched, short-range nuclear weapons deployed overseas (as well as existing stocks of those weapons); and ceasing deployment of tactical nuclear weapons on surface ships, attack submarines, and land-based naval aircraft during “normal circumstances.”⁷ Several days later, Soviet President Mikhail Gorbachev reciprocated and pledged a series of Soviet measures, including eliminating all nuclear artillery munitions, nuclear warheads for tactical missiles, and nuclear mines; removing all tactical nuclear weapons from surface ships and multipurpose submarines; and separating nuclear warheads from air defense missiles for destruction or placement in central storage.

As a result of the PNIs, the United States and Soviet Union eliminated the majority of their tactical nuclear weapons stockpiles at that time, although certain systems exempt from the initiatives remain deployed or in storage. This includes the U.S. B61 gravity bombs, which are deployed in Europe as part of NATO’s extended nuclear deterrence mission, although the PNIs significantly reduced their numbers as well.⁸

Tactical nuclear weapons are inherently destabilizing. By blurring the line between strategic deterrence and warfighting, they lower the threshold for nuclear use and raise the risk of escalation into larger-scale conflicts. We consider their continued perceived utility to lie in the fact that neither the United States nor Russia has a sole purpose doctrine. By prioritizing the strategic mission of nuclear arsenals, that is, deterring and potentially responding to a nuclear attack, a sole purpose doctrine would further limit the roles of tactical nuclear weapons.

Analyzing Potential Pathways to NATO Sole Purpose

With the above considerations on unilateral declarations and tactical nuclear weapons in mind, our discussion sought to examine options for NATO to act unilaterally to reduce the risks posed by tactical nuclear weapons. In particular, we examined the possible issuance of a unilateral declaration to adopt a sole purpose doctrine for NATO nuclear forces.

Current NATO Nuclear Doctrine and Capabilities

NATO’s stated nuclear doctrine is as follows:

The fundamental purpose of NATO’s nuclear capability is to preserve peace, prevent coercion and deter aggression. Nuclear weapons are unique. The circumstances in which NATO might have to use nuclear weapons are extremely remote. Any employment of nuclear weapons against NATO would fundamentally alter the nature of a conflict. The Alliance has the capabilities and resolve to impose costs on an adversary that would be unacceptable and far outweigh the benefits that any adversary could hope to achieve.⁹

NATO’s doctrine is backed by U.S., UK, and French strategic nuclear forces, with U.S. forces as the “supreme guarantee of the security of the alliance.”¹⁰ The United States also deploys B61 gravity bombs in Europe,¹¹ and maintains the capability to set them to various yields; for this reason, some consider them both tactical and strategic nuclear capabilities, although the Department of State notes that “the United States does not envision any use of nuclear weapons to be tactical in character or effect.”¹² The alliance’s doctrine is also backed by allied dual-capable aircraft (DCA) assigned to carry out nuclear strikes in a contingency; advanced conventional capabilities, which include those serving as support to nuclear missions as part of Support of Nuclear Operations With Conventional Air Tactics (SNOWCAT); and missile defense capabilities.

The decision to execute a nuclear strike would require all members of the NATO Nuclear Planning Group (NPG)¹³ to reach consensus and grant explicit, political approval for that mission, in addition to authorization by the U.S. president and UK prime minister.¹⁴ The 2022 NATO Strategic Concept does not go into detail about the circumstances under which the alliance would use nuclear weapons. This policy maintains a level of strategic ambiguity that some argue strengthens NATO’s deterrent threat.

At its core, though, a deterrent threat can only be effective if the party to be deterred views the deterrer as possessing both the capability and the resolve to carry out the stated action. As shown by NATO responses to the Russian military’s “special military operation” in Ukraine, it is difficult to conceive of a non-nuclear contingency—and especially one outside of a NATO state suffering a nuclear attack first—in which a consensus to use nuclear weapons could be reached. If a NATO nuclear mission included the employment of DCA carrying B61 bombs, the allies would likely expect their adversary to respond with its own tactical nuclear weapons in kind (if it had not done so already). This use of tactical nuclear weapons means “nuclear warfighting” would likely take place on NATO soil, with NATO-nation civilians inevitably suffering consequences, even if the targets were military locations.

Moreover, the allies have robust conventional capabilities that could significantly degrade an adversary’s military capability. Given concerns about nuclear warfighting on NATO soil, along with the general aversion of democratically-elected leaders to brandishing nuclear weapons, it seems reasonable that the allies would prioritize relying on their conventional capabilities to avoid nuclear escalation in nearly any circumstance other than for deterring or responding to nuclear weapons.

Adopting a sole purpose doctrine could alleviate these challenges by deemphasizing the role of nuclear weapons in warfighting. Simultaneously, a sole purpose doctrine would still leave potential nuclear employment scenarios on the table, and ambiguously so. In other words, a sole purpose doctrine would not preclude NATO from using nuclear weapons first in a conflict.

In addition to potentially strengthening the credibility of NATO’s deterrent threat, the adoption of a sole purpose doctrine could reinforce NATO’s position as a responsible nuclear defense alliance in the NPT and other international forums. Issuing the doctrine unilaterally could also exert significant pressure on Russia to adopt a reciprocal policy—at least as related to tactical nuclear weapons in Europe.

Opening the Political Pathway Through Capability and Planning Changes

Because the United States, the United Kingdom, and France do not have sole purpose doctrines, it is more pragmatic to think about a NATO sole purpose declaration specifically in terms of the alliance’s tactical nuclear weapons—that is, the sole purpose of the DCA mission, rather than the “supreme guarantee” of U.S., UK, and French strategic forces. This distinction would help strike a balance between maintaining the alliance’s strong strategic nuclear deterrent and reducing the risks of nuclear warfighting on NATO territory.

However, for a political declaration of sole purpose itself to be credible in the first place, it would have to be backed by corresponding changes in NATO’s nuclear capabilities and planning. The following are a series of possible capability and planning changes the alliance could make, led by the United States, given its unique role in facilitating the NATO nuclear mission. For each, we consider the possible risk reduction benefits and drawbacks as well as the feasibility of implementing the change, including garnering a consensus among NPG members. The proposed changes are listed in order of ambition—later changes would likely require some form of adversarial reciprocation to earlier changes before being fully implemented.

Notably, though, it appears unlikely that Russia would undertake reciprocal changes in the current security environment, namely the state of heightened tension resulting from its invasion of Ukraine. To complicate the issue, tactical nuclear weapons have long been a sticking point in U.S.-Russian arms control negotiations. Russia has viewed its tactical nuclear weapons as shoring up its military strength in the face of its conventional imbalance in certain categories, such as fighter aircraft and naval vessels, with NATO. In an atmosphere marked by friction between Russia and NATO, it is highly unlikely that the Putin administration would willingly sacrifice what it sees as a key element of its military strength. Indeed, speaking at the St. Petersburg International Economic Forum in June 2023, Putin stated that tactical nuclear weapons were Russia’s “competitive advantage” and implied that they were vital for influencing the threat calculations of Russia’s adversaries.¹⁵

With this in mind, the following five measures should be seen as a potential long-term road map to ameliorating the security environment.

The Declaration Method

First, NATO partners could announce the sole purpose of the DCA mission through a presidential declaration by members’ heads of state, a joint statement organized by the general secretary, or another form of high-level announcement. Not only could this be more politically feasible than a legally-binding treaty or agreement, it also could allow for some flexibility in terms of the declaration’s implementation timeline. Key challenges associated with such a statement might include concerns about whether the statement constitutes customary international law, or if the statement remains valid if domestic political circumstances in any country significantly shift.

The need to forge a consensus on the declaration of a sole purpose doctrine in the NPG, however, would pose the most fundamental challenge to these efforts. Many states, particularly states that share a border with Russia, have numerous valid, strategic, and historical reasons to be wary of Russian expansionist policies. NATO nations with diverse concerns would need to understand how a sole purpose doctrine could strengthen NATO’s deterrent.

Throughout the process of consensus-building, the United States and United Kingdom would need to assure these states that a shift to a sole purpose doctrine would not jeopardize NATO’s ability to defend their territorial integrity in the event of an Article 5 invocation. Of course, non-nuclear coordination and collaboration are already strong, and include highly-capable conventional weapons (e.g., the U.S.-developed Joint Air-to-Surface Standoff Missiles that are part of the conventional arsenals of Poland and Finland). Efforts to further reassure the allies could take the form of strengthening conventional assurances to the nations most at risk, including by increasing U.S. force presence in Europe, conducting additional exercises aimed at preparing for conventional conflict in a peripheral NATO state, further integrating eastern NATO members in strategic planning exercises, or improving the alliance’s capacity to swiftly reinforce any ally under threat with little to no notice. Additionally, Finland’s recent membership in NATO means that the alliance could potentially expand its maritime presence in the Baltic Sea.

However, such conventional assurance measures would need to be carried out in ways that seek to reduce the risk of fueling the action-reaction cycle. Training exercises meant to strengthen NATO’s ability to defend states under threat by Russia, for example, could be misconstrued as preparations for an invasion of Russia, as could a swift buildup of prepositioned ammunition and equipment in the Baltic states. As part of any effort to assure allies of NATO’s conventional might vis-à-vis a sole purpose doctrine, it would be important to develop an understanding of how these actions would impact Russian threat perceptions.

Nuclear Weapons Employment Guidance

Second, the U.S. president could issue an instruction not to plan for the use of U.S. forward-deployed nuclear weapons in Europe in a tactical manner except in a nuclear contingency. As part of the U.S. nuclear weapons employment guidance, the president could require that these weapons, for example, are only considered usable in response to or under imminent threat of an adversarial nuclear attack against a NATO state and perhaps only as operational support in a larger, strategic nuclear plan.

The president and their advisors, however, would need to think carefully about whether and how to communicate this instruction externally—both to allies and adversaries—without revealing sensitive information. This challenge only highlights the above concerns about the influence of the nuclear-armed states in shaping NATO’s nuclear policy. While U.S. nuclear forces are noted to be the “supreme guarantee of the security of the alliance,” the United States must strike a balance between using this influence to guide NATO nuclear planning and considering—and engaging with—its allies’ concerns and priorities.¹⁶ The notion that the U.S. president could alter the employment guidance of the forward-deployed weapons without gaining NPG consensus on the matter also raises larger concerns about intra-alliance transparency and organizational structure. A decision to change American nuclear weapons employment guidance, as it pertains to NATO, to reflect a sole purpose doctrine, made without the input and agreement of the rest of the NPG could be seen as a schism within NATO, potentially stoking doubts in the cohesiveness of the alliance as a whole. As such, any potential change to American nuclear employment guidance that would impact the alliance should be made in an atmosphere of complete transparency regarding intent, following consultations with the rest of the NPG.

Defining Yields

Third, to reduce ambiguity, the United States could also set its B61 gravity bombs to their maximum yield or remove their variable yield capacity. Maxing out the B61 yields could serve as a clear hardware signal that these weapons are primarily intended to deter—and if necessary, respond to—a nuclear attack, as opposed to serving a potential escalatory function (e.g., providing a more damaging but not entirely all-out strategic response to a conventional attack). Monitoring and verification of this setting, however, would be a substantial challenge, which should not prevent its implementation as a unilateral measure but may make it more difficult to build adversarial confidence in the measure.

However, although this prospective measure is intended to demonstrate NATO resolve to use nuclear weapons only for large-scale, strategic missions, such a shift in posture–particularly if issued amid heightened tensions–could have an opposite effect on strategic stability should an adversary interpret the change as a signal that NATO was preparing to use its now maxed-out B61 bombs in a warfighting capacity.

In addition to the potential impact on an adversary’s decision-making calculus, such a change in yields could elicit a strong public reaction. While maximizing the yield of NATO’s tactical nuclear weapons could place an emphasis on the strategic role of nuclear weapons in the minds of political and military analysts, the subtleties of how this move would be intended to reduce the risks of nuclear warfighting could be lost on the general public. Russia’s invasion of Ukraine and the possibility of a land war in Europe have strengthened NATO coherence, but a public statement announcing that NATO would maximize the yield of the B61 bombs could invigorate domestic opposition to nuclear sharing.

Dual-Capable Aircraft (DCA)

Fourth, the allies could have dedicated aircraft allocated for the nuclear mission—that is, they could fundamentally alter the DCA mission by removing the dual capability of the aircraft. Doing so would eliminate the inherent ambiguity of dual-capable systems and help reduce unintended escalation risks (i.e., the entanglement issue). These nuclear-only aircraft would clearly signal a nuclear mission while all other aircraft would indicate that the allies were undertaking a strictly conventional mission. Given the associated budgetary and domestic political implications of acquiring new aircraft, this would also be a quite costly signal of NATO’s sole purpose resolve.

Yet, the development of aircraft whose sole purpose would be to employ nuclear weapons could pose a number of difficulties. Controversy around the financial cost of existing and future DCA has been intense in the past, so designing, producing, and purchasing aircraft whose sole purpose would be to employ nuclear weapons would likely be a tough sell in some of the relevant nations. While it would reduce the ambiguity of the systems and the potential for unintended escalation that could arise from using DCA in a conventional context, channeling financial contributions toward measures that would strengthen NATO conventional readiness would likely result in a larger benefit to the alliance. In other words, the feasibility of this step is heavily impacted by financial and political constraints.

Weapons Removal

Lastly, the United States could remove any low- or variable-yield forward-deployed gravity bombs from Europe. This could serve as a clear—and, importantly, verifiable—signal of the alliance’s reduced reliance on tactical nuclear weapons. Such a move would have two additional benefits. First, it could help to strengthen the credibility of the alliance’s strategic nuclear deterrent. In a contingency, the alliance would no longer have the option to turn to regionally-deployed, tactical nuclear weapons and instead would have to rely heavily on its strategic assets—thus, in turn, increasing the deterrent value of those assets. Second, it would do away with the—often contentious—political and economic debates surrounding DCA in current host countries.

While the cessation of the nuclear sharing arrangement and the removal of any variable-yield B61 bombs from European soil would be the ultimate signal that NATO was turning away from viewing nuclear weapons as carrying tactical utility, several potential issues stand in the way of implementing this step. The presence of these U.S. nuclear weapons serves as a concrete, tangible signal of the U.S. commitment to the alliance. The removal of these weapons could be interpreted as a signal of a weakened commitment to the alliance, as well as a broader unwillingness to abide by U.S. extended deterrence commitments. This step would only be feasible following intense coordination with NATO allies, as well as allies outside the alliance, such as Japan or South Korea, who are also under the U.S. nuclear umbrella. A crisis of confidence in U.S. extended deterrence commitments could potentially have negative effects on the nonproliferation regime, especially in countries that face acute nuclear threats.

Premature removal of the systems could also weaken potential leverage in future arms control agreements, especially if Russia continues with its stated plans to station tactical nuclear weapons in Belarus. Additionally, it could be seen as an accession to Russian talking points. Russia recently brought nuclear sharing into the NPT context, directly objecting to NATO nuclear sharing in statements made in Main Committee I during the Tenth NPT Review Conference alongside a propagandistic framing of the crisis in Ukraine as a result of NATO expansion and U.S. interference with Ukraine’s political process that resulted in a “creeping coup.”¹⁷ A unilateral removal of nuclear weapons from NATO territory could be interpreted as the alliance ceding control of the narrative to Russia.

Conclusion

With these factors in mind, the timing of any steps taken to implement a credible sole purpose doctrine will be critical to lessen any detrimental effects of that doctrine on allies’ confidence in NATO’s nuclear capability. Given the tensions surrounding Russia’s war in Ukraine, adopting a NATO sole purpose doctrine would require deep consultations, as well as agreement within the alliance that this could be done from a position of strength, and that the most likely outcome would be enhanced security. Yet even in the near term, consultations on the subject could prove valuable for preparing the ground for the institution of a sole purpose doctrine in a less conflictual time. The speed with which this could be achieved is dependent, at least in part, on how events play out in Ukraine. Key factors that will be particularly influential include the non-use of nuclear weapons by Russia, a weakened Russian military presence following the cessation of hostilities, and, to some degree, whether Ukrainian territorial integrity is restored following the end of the war. All of these factors will have some part to play in determining the stability of the strategic environment, which will determine the likelihood that NATO could feasibly and credibly adopt a sole purpose doctrine—even unilaterally.

---

Notes