Table of Contents

Pranay Vaddi departed the Carnegie Endowment for International Peace in May 2021. Every effort was made to ensure that this report was accurate as of October 21, 2021.


In January 2020, the Nuclear Policy Program at the Carnegie Endowment for International Peace initiated a project to define a more promising future for arms control. We aim to mitigate acute nuclear risks by developing practical, concrete, and innovative ideas for interstate cooperation. In particular, we seek to catalyze the restart of U.S.-Russian risk-reduction efforts and to productively engage third parties, especially China.

In December 2020, we published a working paper containing five near-term politically binding proposals for reducing the risks of arms racing and inadvertent escalation.1 After soliciting and receiving valuable feedback, we revised these proposals and are republishing them here—in our final report—along with one additional near-term measure and three ambitious, longer-term concepts. We welcome critiques on all these proposals from officials and experts in China, Russia, and the United States and its allies, as well as from other states. After all, because the consequences of a U.S.-Chinese or a U.S.-Russian nuclear war would be global, every state has an interest in reducing its likelihood.


The governments of China, Russia, and the United States all express support for arms control. They disagree profoundly, however, about its purposes and preconditions. To try to find common ground, this report presents nine detailed practical measures that—implemented individually or as part of a package—would help address each state’s specific security concerns and the shared dangers of arms racing and inadvertent escalation.

Growing Nuclear Dangers

A renewed U.S.-Russian nuclear arms race, which has been largely qualitative so far but could soon turn quantitative, is underway. To compensate for perceived conventional inferiority, Russia maintains a much larger force of nonstrategic nuclear weapons (NSNWs) than the United States does, is fielding new systems, and may be increasing its overall number of nonstrategic warheads. In response, the United States is developing and deploying its own new types of NSNWs. (Russia and the United States generally use the term “strategic” to describe nuclear weapons with sufficient range to reach the other’s homeland from deployment locations in the possessor’s homeland or, in the case of sea-launched ballistic missiles, from firing locations well away from the other’s coast.)

At the strategic level, Russia believes that the United States is seeking capabilities—including high-precision conventional weapons and ballistic missile defenses—to undermine its nuclear deterrent. Moscow’s response has included the development and deployment of various new kinds of strategic weapons. The 2010 New Strategic Arms Reduction Treaty (New START) helps to manage this competition by limiting all currently deployed U.S. and Russian strategic weapons, though it will expire in 2026.

Like Russia, China believes that the United States seeks to undermine its nuclear deterrent. As a result, Beijing is improving and expanding its long-range nuclear forces without giving any indication of its intended endpoint. Separately, it is also modernizing and enlarging its force of regional missiles, including dual-use weapons, in a likely effort to acquire more credible options for limited nuclear use. (Dual-use weapons can accommodate a nuclear or nonnuclear warhead.)

The vulnerability of nuclear C3I systems creates the possibility that Chinese or Russian operations against the United States could also lead to inadvertent escalation.

In a deep crisis or a conventional conflict between the United States and China or Russia, Chinese and Russian concerns about force vulnerability could spark inadvertent escalation. This risk is increasing because of the growing entanglement between the nuclear and nonnuclear domains. Such entanglement includes nonnuclear threats to nuclear forces and their command, control, communication, and intelligence (C3I) systems and a reliance on dual-use C3I capabilities (that is, C3I capabilities that support nuclear and nonnuclear operations). Indeed, the vulnerability of nuclear C3I systems creates the possibility that Chinese or Russian operations against the United States could also lead to inadvertent escalation.

Unilateral responses to these dangers typically involve trade-offs between different escalation risks. For example, China’s development of a strategic early-warning system that could enable it to launch its nuclear forces before they were destroyed in an incoming attack—thus enhancing their survivability—also creates the danger that it might mischaracterize a U.S. missile test as an attack.

The Purpose and Politics of Arms Control

Arms control—a term used here in its broad, original sense to mean “all the forms of military cooperation between potential adversaries” intended to improve mutual security—offers a proven and potentially powerful approach to managing nuclear risks. A first step is for Russia and the United States to commence negotiations toward a follow-on to New START. To avoid the overload and potential collapse of these negotiations, the scope of a New START follow-on should be limited to strategic offensive arms. As such, it could not manage every critical risk. Its focus on strategic arms would preclude the inclusion of Russia’s and the United States’ NSNWs. As a bilateral agreement, it would not regulate any Chinese capabilities and would also therefore be the wrong forum to manage the danger of misidentifying a missile test as an attack. And because its scope would be restricted to offensive arms, it would do nothing to address Chinese and Russian concerns about ballistic missile defense and not enough to manage threats to nuclear C3I capabilities.

James M. Acton
Acton holds the Jessica T. Mathews Chair and is co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace.
More >

This report offers nine proposals—six near-term politically binding transparency and confidence-building measures and three more ambitious treaty concepts—that would help address these lacunae. These proposals would also help all three states—especially Russia and the United States—demonstrate commitment to their disarmament obligations and hence bolster the nonproliferation regime.

While each proposal raises some unique difficulties, a few implementation challenges would be common to many of them. Russia and the United States already have a dedicated channel for exchanging arms control notifications. China and the United States (and possibly China and Russia) would have to create one. In doing so, Beijing would be tacitly acknowledging the potential value of transparency—a step that it has not yet taken. Separately, a number of these proposals would require inspections on the territory of U.S. allies. While such inspections could be politically sensitive, the 1987 Intermediate-Range Nuclear Forces (INF) Treaty provides a clear precedent.

Some proposals would provide concrete benefits to all participants, while others would address the particular concerns of one state and therefore need to be negotiated as part of a mutually beneficial package.

China is the most skeptical of arms control and has recently emphasized its lack of interest in negotiations over nuclear limitations. However, it has failed to indicate whether it believes that its security could be enhanced by other forms of arms control and should now consider what concessions it would require from Washington in return for addressing U.S. concerns.

The United States is concerned about Russia’s habit of violating arms control agreements, while Russia is concerned about the United States’ habit of abrogating them. However, they are moving closer on the question of format. The United States is generally supportive of politically binding transparency and confidence-building measures. Russia, which has traditionally been skeptical of them, has recently shown more interest. The hybrid approach advocated here—which starts with a treaty that constrains strategic offensive arms implemented alongside separate transparency and confidence-building measures—offers the most practical and plausible way forward. Moreover, politically binding agreements can facilitate the development of legally binding ones.

Six Near-Term, Politically Binding Measures

The following six proposals are intended to quickly reduce the risks of arms racing and inadvertent escalation through politically binding agreements:

  • A U.S.-Russian data exchange for sea-launched cruise missiles (SLCMs) and nonnuclear sea-launched boost-glide missiles (SLBGMs)
  • A U.S.-Russian transparency regime for empty actual or suspected warhead storage facilities
  • A U.S.-Russian confidence-building regime for European Aegis Ashore ballistic missile defense installations
  • A U.S.-Chinese fissile material cutoff and transparency regime
  • A trilateral launch notification agreement for ballistic missiles, missile defense tests, and space launches
  • A trilateral agreement to establish keep-out zones around high-altitude satellites

The first three proposals, which involve Russia and the United States, aim to manage capabilities that cannot realistically be limited in their next bilateral treaty. The other three aim to engage China with the objectives of heading off a Chinese-U.S. arms race, reducing the danger of escalation as the result of a test or space launch, and protecting the survivability of key nuclear C3I assets.

First, Russia and the United States should, twice a year, exchange confidential declarations of the number of deployed nuclear-armed SLCMs, nonnuclear SLCMs, and nonnuclear SLBGMs (disaggregated by two range categories). Because of their potentially long ranges and high accuracies, SLCMs and, in the future, SLBGMs could drive arms racing and crisis instability. These dangers could be heightened if Russia or the United States overestimates the other’s current or future deployments. Because limiting SLCMs or SLBGMs in a follow-on to New START would present insurmountable challenges—with the sole exception of making nuclear-armed SLBGMs accountable—transparency is a more practical way forward. Any security risks associated with this exchange should be minimal because it would not reveal a capability that was previously unknown to the other state or the precise mix of weapon types deployed—let alone the armaments on any particular ship.

Thomas MacDonald
Thomas MacDonald is a fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace.

Second, Russia and the United States should agree, on a politically binding basis, to reciprocal inspections of two to five pairs of empty actual or suspected warhead storage facilities to demonstrate that they do not contain nuclear warheads (here “empty” connotes the absence of all nuclear warheads, regardless of type). Ambiguity around the location of NSNWs creates serious risks. The possible presence of nuclear warheads in the Russian enclave of Kaliningrad, for example, exacerbates tensions—potentially unnecessarily if, in fact, none are present. Moreover, in a conventional conflict, ambiguity could prove escalatory by leading to unnecessary attacks on storage facilities in an effort to forestall nuclear use. Inspections of empty facilities could help to reduce these risks.

Facilities would be selected on the basis of mutual consent, including from the host state for a facility located on the territory of the North Atlantic Treaty Organization (NATO) outside of the United States. Following facility selection, Russia and the United States would exchange baseline information, including site diagrams, and negotiate inspection boundaries.

Inspections should occur within sixty days of site selection. Following preliminary inspection procedures, the duration of the facility inspection should be limited to twelve hours. During that period, the inspection team should be given access first to any vehicles designated for inspection and then to any weapon storage containers and rooms that it selects in whatever order it chooses. The host state should have the right to shroud, in advance of the inspection, any items other than warhead storage containers that it deems sensitive. The inspection team should have the right to request the opening of any warhead storage container to verify that it does not contain a nuclear warhead. It should also have the right to employ radiation detection equipment to confirm that any shrouded objects, storage containers for nonnuclear munitions, and other objects do not contain nuclear material.

The technical challenges associated with this proposal appear manageable. From a political perspective, this proposal would not require negotiations over limits on NSNWs, thus respecting a Russian redline, and would build experience and confidence in inspecting warhead storage facilities, thus advancing the U.S. goal of a more comprehensive treaty. Because facilities must be selected by mutual consent, the host state could always veto an inspection request that presented insurmountable difficulties. This veto power represents an important safeguard—though if it were used too often, the proposed agreement would likely fall apart amid reciprocal accusations of bad faith.

Third, Russia and the United States should agree to a package of measures on European Aegis Ashore ballistic missile defense installations:

  • Russia should, at the invitation of the United States, observe one flight test of a Standard Missile-3 (SM-3) Block IB interceptor and one of an SM-3 Block IIA interceptor in order to measure, with its own equipment, each interceptor’s burnout speed (the maximum speed, which is reached immediately after a rocket’s motors have cut off or burnt out).
  • The United States should commit to (1) notifying Russia in advance of the first European deployment of any type of missile defense interceptor with a burnout speed greater than 3 kilometers per second (1.9 miles per second) that is not currently deployed there and (2) inviting Russia to observe, at least sixty days prior to the interceptor’s first deployment in Europe, a flight test in order to measure the interceptor’s burnout speed.
  • The United States should reaffirm to Russia the exclusively defensive purpose of European Aegis Ashore installations and commit to refraining from (1) loading offensive missiles into European Aegis Ashore launchers and (2) modifying such launchers so they become capable of launching offensive missiles.

Russia is concerned that the United States’ deployment of SM-3 interceptors in Europe to defend against Iranian ballistic missiles may threaten its ability to target the United States with intercontinental ballistic missiles (ICBMs). Moreover, the launchers for these interceptors are adapted from the U.S. Navy’s MK-41 Vertical Launching System, which is used on ships equipped with the Aegis air and missile defense system to launch SLCMs and other missiles as well as SM-3s. The possibility that so-called Aegis Ashore launchers could also be used to fire offensive missiles, particularly cruise missiles—in spite of U.S. statements to the contrary—is a second concern for Moscow.

These concerns could motivate Moscow to attack Aegis Ashore installations preemptively in a crisis or conflict. They also complicate the development of arms control agreements—including measures to manage the new kinds of strategic weapons that Russia is developing to penetrate U.S. missile defenses. These risks could be reduced by increasing Russia’s confidence in the capabilities of Aegis Ashore launchers.

Russia could monitor U.S. interceptor flight tests by positioning its missile range instrumentation ship on the high seas near the U.S. test site in Hawaii. The approach to verifying the exclusively defensive nature of Aegis Ashore installations would depend on whether Russia and the United States could jointly identify externally observable distinguishing features between such installations and their sea-based equivalents that would preclude the former from launching offensive missiles. If they could, verification would be based on national technical means (NTM) or inspections of external features. If not, the United States could permit Russian inspectors to select and view the inside of an agreed number of Aegis Ashore launchers to check that they are loaded with missile defense interceptors. Any form of on-site access would require the consent of the host state.

Pranay Vaddi
Pranay Vaddi was a fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace.
More >

U.S. critics would probably argue that disclosing burnout speeds to Russia could compromise national security. This information, however, would not meaningfully assist Russia (or any third party to which Russia disclosed this information) to defeat U.S. defenses.

Russia’s newfound willingness to consider politically binding confidence-building measures presents an opening for this proposal. To improve the prospects for progress, the administration of U.S. President Joe Biden should frame this proposal as the first step of a long-term process to address a wider range of concerns that could potentially include the development of legally binding instruments.

Fourth, China and the United States should declare a joint politically binding cutoff in the production of weapon-usable fissile material. If China is unwilling to agree to a complete cutoff because it is still producing or plans to produce fissile material for civil purposes, it should agree to a cutoff in production for military purposes and to place all newly produced highly enriched uranium and separated plutonium under International Atomic Energy Agency (IAEA) safeguards. The two states should also commit to talks about mutual confidence building and to exchange confidential declarations about their stockpiles of weapon-usable fissile material.

There is broad consensus within the U.S. national security community about the importance of engaging China in arms control—not least to prevent China from challenging the United States in warhead numbers. Washington, however, cannot force Beijing to negotiate. Instead, if the United States is to have any chance of engaging China, it will have to craft proposals that mitigate Chinese concerns about transparency, while also identifying suitably valuable American concessions that could form part of a mutually beneficial quid pro quo. Because implementing this proposed measure would reveal only an approximate maximum size for China’s nuclear arsenal and nothing about weapon locations, it would help manage Chinese concerns about transparency.

The United States unilaterally ceased the production of fissile material for any purpose, civil or military, almost thirty years ago and has no plans to restart it. There are widespread but unconfirmed reports that China has ended the production of fissile material for military purposes, though the country has ambitious plans to develop a civil reprocessing program. The U.S. Defense Intelligence Agency assesses that China’s extant fissile material stockpile is not large enough for China to challenge the United States in warhead numbers. A credible cutoff in military fissile material production should therefore be sufficient to address U.S. concerns, so long as China places any newly produced civil fissile material under IAEA safeguards.

After declaring a cutoff, China and the United States should exchange confidential declarations about their stockpiles of weapon-usable fissile material and discuss any compliance concerns they might have, with the aim of developing targeted verification measures.

In verifying a cutoff, the primary challenge would be confirming the nonproduction of highly enriched uranium at enrichment facilities—which could require physical access. To be politically palatable, reciprocity would be required. By contrast, the comprehensive verification of stockpile declarations would be functionally impossible; ultimately, China and the United States would have to decide whether or not they were better off receiving additional information, even if they could not verify it.

This proposal would benefit the United States, which has an excess of fissile material, more than China, which probably wants to retain the option to produce more. Nonetheless, Beijing has three potential motivations to explore this proposal. First, it could be adopted as part of a mutually beneficial package. A politically binding agreement not to test or deploy space-based missile defenses could be a suitable quid pro quo. Second, the proposal would help China gain deeper insight into the U.S. fissile material stockpile. Third, it would presumably be more acceptable to China than the United States’ preferred alternative of binding limits on nuclear forces.

Fifth, China, Russia, and the United States should agree to notify one another of (1) all space launches, (2) all test launches of ballistic or boost-glide missiles, and (3) all test launches of missile defense interceptors and of target missiles (subject, in each case, to defined conditions). If mistaken for an attack, a ballistic missile test, missile defense test, or space launch could spark escalation. Similarly, if preparations for a test launch were mistaken as preparations for an attack, they could invite preemption. While these risks may be low in peacetime, they could rise significantly during times of heightened tensions and, because of technological developments, could soon arise in a U.S.-Chinese crisis as well as a U.S.-Russian one.

Notifications before test or space launches can help reduce these risks; indeed, U.S-Russian and Chinese-Russian notification agreements are in place. The existing regime has notable gaps, however. China and the United States have not agreed to exchange any launch notifications. The range thresholds that trigger notification requirements are too large. And, no state has committed to providing notifications about tests of boost-glide missiles, missile defense tests, or sub-orbital space launches.

Compared to other concepts for trilateral arms control, the political obstacles facing this proposal are small—though three challenges that are significant in absolute terms would have to be overcome. First, both China and the United States are more concerned about deliberate aggression than they are about inadvertent escalation, though both have recognized the possibility that escalation might not be deliberate. Second, they may disagree about what steps, if any, should follow this proposal—but this should not prevent them from supporting it if they believe it would enhance their security. Finally, all three states may be concerned that launch notifications could cue additional espionage activities to monitor launches. Such warning, however, would not significantly enhance the effectiveness of the intelligence-collection capabilities that each state already has or is developing.

Sixth, China, Russia, and the United States should make a joint political commitment to establish keep-out zones around their high-altitude satellites—that is, each should commit to maintain minimum separation distances between its satellites and the satellites in high-altitude orbits that belong to other participants. Military communication and early-warning satellites in high-altitude orbits play critical roles in nuclear C3I systems. A repositioning operation that brought a satellite into proximity with one involved in nuclear operations could be misconstrued as preparation for an attack against the latter. Moreover, many satellites involved in nuclear operations are dual-use. As a result, in a conventional conflict, they might be attacked in an attempt to disrupt nonnuclear operations being conducted by their possessor. Such inadvertent threats to, and attacks on, space-based nuclear C3I capabilities would risk being interpreted as preparations for nuclear war—potentially sparking catastrophic escalation.

Keep-out zones could reduce the threat posed by co-orbital anti-satellite weapons to high-altitude satellites in two key ways, even while recognizing that such zones could not physically prevent attacks in a conflict. First, they would mitigate the danger of unintended threats to satellites resulting from nonhostile repositioning operations. Second, even if one participant decided to attack another’s satellites, keep-out zones could buy time.

To ease implementation, repositioning operations that led one satellite to enter another’s keep-out zone would be permitted—subject to various rules such as providing advance notification of the maneuver. Moreover, only the satellites declared by each participant would be afforded the protection of keep-out zones.

Participants would verify compliance with this proposed measure by using their own space situational awareness capabilities. The United States is likely already capable of effective verification. It is unclear whether Russia and China are too—though, if not, they are probably on a trajectory to acquire the necessary capabilities.

One key political challenge is that China and Russia appear to want the ability to hold U.S. satellites in high-altitude orbits at risk. However, as they are investing heavily in their own high-altitude military satellites, including for nuclear C3I, they may be interested in this proposal.

Three Longer-Term, Legally Binding Measures

Over the longer term, bilateral and trilateral treaties could be negotiated to build a more durable and robust risk-reduction architecture. Three such agreements, with varying levels of ambition, are proposed here:

  • A trilateral treaty to prohibit the development and deployment of space-based missile defenses
  • A trilateral treaty to limit ground-based missile launchers, sea-launched ballistic missile (SLBM) launchers, and bombers
  • A U.S.-Russian limit on all nuclear warheads

First, China, Russia, and the United States should conclude a treaty prohibiting the testing or deployment of space-based missile defense weapons. Space-based missile defenses are capable, at least in theory, of addressing some key weaknesses of terrestrial missile defense systems. Russian and Chinese concerns about space-based defenses contribute to arms racing and exacerbate escalation risks, while complicating the development of agreements to manage these dangers. However, the development of space-based missile defenses presents daunting technical challenges and carries potentially exorbitant costs; for these reasons, the United States is unlikely to ever deploy a meaningful capability.

A trilateral prohibition on the testing and deployment of any space-based weapon designed to counter ballistic or boost-glide missiles would apply to both kinetic and nonkinetic weapons but would not affect the deployment of space-based sensors to detect missile launches or track missiles during flight. The prohibition would be verified through NTM, with efforts primarily focused on assessing compliance with the ban on testing. To gain a meaningful operational capability, a lengthy testing campaign would be needed. Such a campaign would be difficult to conceal against multiple intelligence-collection techniques, even if a state were sometimes successful in hiding individual tests.

Russia and China would likely support this proposal. The primary political impediment to its conclusion would be domestic resistance in the United States, stemming from an understandable though unattainable desire to develop a comprehensive defense against ballistic missile attack. That said, limitations on space-based interceptors, whose development costs would be prohibitive, may be somewhat more palatable for the United States than limitations on ground-based missile defenses. Furthermore, if China and Russia want a prohibition of space-based missile defenses, they will have to make significant concrete concessions to the United States in return.

Second, China, Russia, and the United States should conclude a treaty that would limit each party to equal total numbers of launchers for ground-launched cruise missiles, ground-launched ballistic missiles, and ground-launched boost-glide missiles with ranges over 475 kilometers (295 miles); SLBM launchers; and bombers with ranges greater than 2,000 kilometers (1,200 miles). Such limits could help prevent arms racing and mitigate escalation risks by curtailing the threat posed to national and military leaders and to nuclear forces and their enabling capabilities.

This agreement would limit launchers, rather than smaller items like warheads or missiles, to reduce verification difficulties significantly. Ground-based launchers would be accountable if used to launch missiles with a range in excess of 475 kilometers—and not 500 kilometers (310 miles) as under the INF Treaty—to bypass the controversy over the range of the SSC-8, a Russian ground-launched cruise missile that the United States claims, almost certainly correctly, was developed in violation of that treaty. In a major concession to China and Russia, the United States would agree that, for the purposes of treaty implementation, its Aegis Ashore launchers met the definition for launchers of ground-launched cruise missiles and were thus accountable. In a major reciprocal concession to Washington, Beijing and Moscow would agree that the treaty should not constrain SLCM or SLBGM launchers.

It appears that China, Russia, and the United States currently possess roughly equal numbers of accountable launchers and accountable bombers (though there are large uncertainties in the estimates for China and particularly Russia), and it seems possible this rough equality will persist. To make the agreement more politically palatable, the chosen central limit should be slightly higher than any state’s arsenal of accountable launchers and accountable bombers at the time of entry into force.

To facilitate verification, China, Russia, and the United States should exchange baseline information, comprehensive semiannual updates, and regular notifications about accountable launchers and accountable bombers. The three parties should be able to use NTM, including satellite imagery, to verify numbers of accountable bombers, fixed accountable ground-based launchers (silos), and SLBM launchers. To facilitate verification, they should agree not to interfere with one another’s NTM.

On-site inspections would likely be needed to verify mobile accountable ground-based launchers. These inspections would be modeled on New START’s provisions for inspections of mobile ICBM launchers, though would be less intrusive because there would be no requirement to display missile front sections, revealing the attached reentry vehicles and other sensitive objects.

The proposed treaty is built on Russia’s and the United States’ extensive experience in implementing limits on heavy bombers and various types of missile launchers pursuant to past arms control agreements. That experience suggests that verification is feasible and that the risk of a party’s retaining a militarily significant number of undeclared accountable launchers—mobile ground-based launchers, in particular—should be manageable.

There would be many political barriers to reaching an agreement, including Chinese concerns about a radical increase in transparency. Most acutely, many U.S. officials and analysts would likely argue that the United States should build up its force of regional missiles before seeking limits through arms control. One problem with this approach is that deploying mobile ground-launched missiles to allied territory, where they would be militarily useful, would likely prove politically fraught. Moreover, while some buildup may be unavoidable, it risks stimulating arms racing. The question that decisionmakers in Washington—and Beijing and Moscow, for that matter—must ask themselves is how the risks of trying to break away from today’s rough equality compare to the risks of living with it.

Third, Russia and the United States should work toward a treaty that would limit each state’s total number of nuclear warheads—irrespective of their type, location, or deployment status and whether or not they are awaiting dismantlement. New START limits the approximately 2,700 nuclear warheads deployed on ICBMs and SLBMs—less than 25 percent of Russia and the United States’ combined total inventory of warheads. No other warheads—those in storage, those being transported, and those that have been retired and are awaiting dismantlement—are even indirectly accountable. Given the concerns of the United States and its allies over Russia’s large force of nonstrategic nuclear warheads, there is considerable interest across the U.S. political spectrum in a warhead limit. Russia, by contrast, has little interest in such a treaty. To have any chance of Russia’s agreeing to it, the United States would have to offer a very significant concession in return, such as limits on missile defense.

The technical challenges associated with verifying a warhead limit would likely preclude agreement today. Verification would involve data exchanges and notifications (which would be relatively straightforward) and on-site inspections (which would be much more challenging), supplemented by each state’s NTM capabilities.

A treaty would not need to contain specific verification provisions for warheads deployed on ICBMs, SLBMs, and heavy bombers, which are accountable under New START and should continue to be under a successor. However, the agreement would require inspections of warhead storage facilities. All warheads in transport would be exempt from inspections.

Inspections would face a fundamental difficulty: The classification rules surrounding warheads would prevent inspectors from viewing them directly or conducting any measurements that could reveal sensitive design information. Therefore, verification would largely focus on warhead storage containers on the assumption that, to prevent nuclear accidents, Russian and U.S. warheads are always kept in such containers when not attached to strategic delivery vehicles.

In many circumstances, classification rules would not impede effective verification since the host state would generally gain no advantage by claiming that an empty storage container held a warhead. Prior to warhead dismantlement, however, such a claim could enable cheating (by subsequently “dismantling” those nonexistent warheads, the state could retain more warheads than it had declared). It therefore would be necessary to verify that an object declared to be a warhead awaiting dismantlement really was an actual warhead. This process would be challenging for two reasons: first, it would be necessary to define what a warhead is in terms of measurable criteria, and second, the unauthorized disclosure of classified information during the measurement process would need to be prevented.

Technological solutions to these problems have been proposed and developed. A warhead could be defined in terms of certain attributes or its similarity to a template, and a so-called information barrier could sit between the detection equipment and the inspector to provide an approved output. However, these solutions are far from being ready to use in treaty verification. Moreover, given the exceptional sensitivity of assembly/disassembly facilities, which were not intended to be transparent, designing and implementing a credible verification system could prove challenging.

Overcoming these challenges requires more individual and joint research. Individual efforts should include restarting national research programs on warhead-level arms control. Russia and the United States should also undertake the following cooperative efforts, which would realistically require some improvement in their political relationship:

  • Restart joint research into warhead verification
  • Start joint studies into inspections at warhead storage facilities and commit to extending such studies to include assembly/disassembly facilities in the future
  • Negotiate reciprocal inspections to verify the absence of nuclear warheads at empty actual or suspected warhead storage facilities
  • Negotiate a warhead information exchange for implementation on a politically binding basis
  • Consider whether New START’s replacement should limit all warheads located on ICBM, SLBM, and heavy bomber bases, whether deployed or in storage


Although these proposals vary significantly in their level of ambition, none likely present any currently insurmountable technical barriers—except for the treaty to limit all warheads for which significant additional preparatory work would be required. Moreover, implementing any of them would help to reduce nuclear dangers. We therefore urge Beijing, Moscow, and Washington to adopt them.

While calling for progress, however, we recognize that politics create real roadblocks, especially to the more ambitious proposals. The pace of progress on arms control will be constrained by fraught international relationships and divisive internal politics that create incentives for leaders not to cooperate with rivals. Indeed, generating the necessary political will to turn these nine proposals into reality will be challenging. There may be no simple fix, but history demonstrates that political barriers are not immutable. While it is impossible to predict when opportunities for arms control will arise, China, Russia, and the United States and NATO should consider and refine proposals now to enable rapid progress when political conditions are favorable.

Each state should ask itself whether its interests would be better served by a broader conception of its security goals—one that encompasses the prevention of arms racing and the mitigation of inadvertent escalation risks as well as the development of effective deterrence capabilities. Arms control can be a powerful tool for navigating the trade-offs in pursuing these objectives and hence for better managing the risks inherent to enhancing security through threats of catastrophic destruction.


C3I command, control, communication, and intelligence
EODF externally observable distinguishing feature
EPAA European Phased Adaptive Approach
HEU highly enriched uranium
HIMARS High Mobility Artillery Rocket System
IAEA International Atomic Energy Agency
ICBM intercontinental ballistic missile
INF Intermediate-Range Nuclear Forces (Treaty)
ITU International Telecommunication Union
NATO North Atlantic Treaty Organization
New START New Strategic Arms Reduction Treaty
NSNW nonstrategic nuclear weapon
NTM national technical means
SALT Strategic Arms Limitation Talks
SLBGM sea-launched boost-glide missile
SLBM sea-launched ballistic missile
SLCM sea-launched cruise missile
SM-3 Standard Missile-3
SSBN nuclear-powered ballistic missile submarine
SSGN SSBN converted to carry cruise missiles
START Strategic Arms Reduction Treaty
UID unique identifier


This work was made possible by generous support from the Dutch Ministry of Foreign Affairs; the Embassy of Japan in Washington, DC; the German Federal Foreign Office; the Ministry for Foreign Affairs of Finland; the Royal Norwegian Ministry of Foreign Affairs; the Swiss Federal Department of Foreign Affairs; the Carnegie Corporation of New York; the New-Land Foundation; and the Prospect Hill Foundation. For research assistance, we are grateful to Megan DuBois, Garrett Hinck, Gaurav Kalwani, and Natalie Montoya. For their outstanding editing, design, and production work, we thank Sam Brase, Lori Merritt, and Jocelyn Soly. For helpful conversations and insightful comments on earlier drafts, we are grateful to Mike Albertson, Andrey Baklitskiy, Konstantin Bogdanov, Linton Brooks, Elaine Bunn, Evgeny Buzhinskiy, Jessica Cox, Fiona Cunningham, Rose Gottemoeller, Zia Mian, Jim Miller, William Moon, John Ordway, George Perkovich, Steven Pifer, Pavel Podvig, Sergey Oznobishchev, Sergey Rogov, David Rust, Victoria Samson, Benjamin Silverstein, Nikolai Sokov, Dmitry Stefanovich, Steve Steiner, Brian Weeden, David Wright, Wu Riqiang, and Tong Zhao, and other private meeting and workshop participants. The authors of this paper are solely responsible for its contents.


1 James M. Acton, Thomas D. MacDonald, and Pranay Vaddi, “Revamping Nuclear Arms Control: Five Near-Term Proposals,” Carnegie Endowment for International Peace, December 2020,