The Future of U.S. Nuclear Weapons Policy


Executive Summary of the National Academy of Sciences Report

The National Academy of Sciences (NAS) released a major policy report on June 17, entitled The Future of U.S. Nuclear Weapons Policy , recommending substantial changes in U.S. nuclear weapons policies and forces to bring them into conformity with the post-Cold War environment. The report's central recommendation is that the use of nuclear weapons be limited to a core mission of deterring the use of nuclear weapons by others.

The study calls for a program of progressive constraints to reduce U.S. and Russian nuclear arsenals to 1,000 total warheads each and then, if security conditions permit, to a few hundred warheads, provided adequate verification procedures and transparency measures have been implemented. Parallel steps are also necessary to reduce high alert levels and to substitute much more selective targeting than now incorporated in present war plans. While the path to the prohibition of all nuclear weapons is not yet clear, the report examines the conditions that would have to exist for this to be acceptable and suggests various ways it might be achieved.

The report was prepared by the NAS Committee on International Security and Arms Control (CISAC), a group of distinguished scientists, retired senior military officers and experts policy analysts, most of whom have been closely associated with various aspects of nuclear security affairs. (See p. below.)



The debate about appropriate purposes and policies for U.S. nuclear weapons has been under way since the beginning of the nuclear age. With the end of the Cold War, the debate entered a new phase, propelled by the post-Cold War transformations of the international political landscape and the altered foreign policy challenges and opportunities that these changes are bringing about. This report—based on an exhaustive reexamination of the issues addressed in the committee's 1991 report on The Future of the U.S.Soviet Nuclear Relationship—describes the state to which U.S. and Russian nuclear forces and policies have evolved since the Cold War ended, the reasons why further evolution is desirable, and the shape of a regime of progressive constraints responsive to these reasons. It concludes with a discussion of the conditions and means under which, in the longer term, it could become desirable and feasible to prohibit the possession of nuclear weapons altogether.



The first Strategic Arms Reduction Treaty (START I), signed in 1991 as the Cold War was ending and now being implemented by both the United States and Russia, will reduce the number of strategic nuclear warheads deployed by the two countries from 13,000 and 11,000, respectively, to about 8,000 each. START II, signed in 1993 and ratified by the United States in early 1996 but not yet (as of this writing) ratified by Russia, would further limit the number of deployed strategic warheads to 3,000 to 3,500 on each side. At the Helsinki summit in March 1997 Presidents Clinton and Yeltsin agreed to seek a START III treaty with a level of 2,000 to 2,500 deployed strategic nuclear warheads. Unilateral initiatives since the Cold War began winding down have also reduced very substantially the numbers of deployed non-strategic warheads, especially on the U.S. side. In addition, nuclear testing has ended, the United States and Russia have agreed not to target their missiles against each other on a day-to-day basis, and production of weapons-grade fissile material has stopped in the United States and is expected to stop soon in Russia.

These actions have unambiguously halted and reversed the bilateral nuclear competition that was the most conspicuous characteristic of the Cold War's military confrontation but, unfortunately, have not sufficiently altered the physical threat that these weapons pose. The reduced forces could still inflict catastrophic damage on the societies they target or could target, and the thousands of non-deployed and non-strategic nuclear warheads not addressed by the START process and likely to be retained without further agreements will pose substantial risks of breakout, theft, or unauthorized use. In addition, the United States and its NATO allies retain their Cold War "weapons of last resort" doctrine that allows the first use of nuclear weapons if deemed necessary to cope with non-nuclear attacks, and Russia has announced that it is abandoning the Soviet Union's no-first-use pledge in order to adopt a position similar to NATO's.

The basic structure of plans for using nuclear weapons appears largely unchanged from the situation during the Cold War, with both sides apparently continuing to emphasize early and large counterforce strikes and both remaining capable, despite reductions in numbers and alert levels, of rapidly bringing their nuclear forces to full readiness for use. As a result, the dangers of initiation of nuclear war by error (e.g., based on false warning of attack) or by accident (e.g., by a technical failure) remain unacceptably high. (On the Russian side, the dangers of erroneous, accidental, or unauthorized nuclear weapons use may be even higher than during the Cold War because of subsequent deterioration of the military and internal-security infrastructure and of morale.) The continuing competitive assumptions underlying some official discussions of the U.S. Russian nuclear relationship, when coupled with the postures of the forces and the potential for destabilizing deployments of ballistic missile defenses, pose the risk that the arms control fabric woven during the Cold War and immediately thereafter could unravel.

In addition, continued actions by the United States and Russia to reduce their nuclear arsenals—and to reduce the roles assigned to those arsenals—are needed to help bring the other declared and undeclared nuclear weapons states into the arms reduction process and to strengthen the global nonproliferation regime. The effectiveness of that regime depends on the full support and cooperation of a large number of non-nuclear weapons states in the maintenance of a vigorous International Atomic Energy Agency with the inspection powers and resources to do its job, in the implementation of effective controls on the transfer of sensitive technologies and in the creation of transparency conditions conducive to building confidence that proliferation is not taking place. The degree of commitment of the non-nuclear weapons states to these crucial collective efforts will surely depend at least in part on impressions about whether the nuclear weapons states are working seriously on the arms reduction part of the global nonproliferation bargain.



During the Cold War, nuclear deterrence was the bedrock of U.S. strategy for preventing both nuclear war and major conventional war because a more effective alternative was not apparent: the adversarial U.S.Soviet relationship made it seem imprudent to rely on good intentions to preclude nuclear attack or massive conventional assault; the character of nuclear weapons and the diverse means for delivering them meant that attempts to defend the United States or its allies against nuclear attacks on their populations could be overcome with much less effort than would have to be invested in the defenses; highly survivable basing modes for significant parts of each side's nuclear forces made it impractical to execute a disarming first strike even if conflict seemed imminent; and concern about the powerful conventional forces of the Warsaw Treaty Organization (and, in Asia, those of China and North Korea) motivated the United States and its allies to adopt a first-use-if-necessary nuclear posture to deter large-scale conventional attacks.

But nuclear deterrence itself was (and is) burdened with an array of dilemmas and dangers. For example, deterrence is likely to succeed only if there are credible plans for what to do if it fails, but constructing such plans is exceedingly difficult, and attempts to make the threat of nuclear retaliation credible can be seen as aggressive advantage seeking by the other side. This raises tensions, stimulates arms races, or increases the chance of nuclear war from crisis instability or accident. In addition, the assertion by some countries of a need and a right to have a nuclear deterrent may encourage additional countries to assert the same need and right, leading to further nuclear proliferation.

This committee has concluded that the dilemmas and dangers of nuclear deterrence as practiced by the United States in the past can and should be alleviated in the post-Cold War security environment by confining such deterrence to the core function of deterring nuclear attack, or coercion by threat of nuclear attack, against the United States or its allies. That is, the United States would no longer threaten to respond with nuclear weapons against conventional, chemical, or biological attacks. Given adequate conventional forces, the active and conspicuous role given to nuclear weapons during the Cold War can be greatly reduced without significant adverse effect on the probability of major war or on this country's ability to deal effectively with regional conflicts where its vital interests and those of its allies are at stake. The committee believes that Russia and the other nuclear weapons states can be persuaded to reach a comparable conclusion.

In all likelihood the United States will consider it necessary to continue to rely on the core function of nuclear deterrence as long as nuclear weapons continue to exist in the possession of states that might consider using them against this country or its allies. The committee assumes that some—although it is hoped not all—other nuclear weapons states will similarly consider it necessary to retain some nuclear weapons for "core deterrence." But the size and scope of the efforts deemed necessary by the United States and others to fulfill the core function presumably will shrink in parallel with what the committee hopes is the declining plausibility that any state would consider mounting a nuclear attack on anyone. Moreover, there are strong reasons to make every effort to hasten the arrival of international conditions in which threats of nuclear attack are simply no longer thinkable, so that the practice of deterrence with all its dilemmas and dangers would no longer be necessary.

As long as nuclear weapons exist, this very existence will exert a deterrent effect— existential deterrence—against unrestricted conventional war among the major powers, since it will be recognized that, in a world with nuclear weapons, such conflicts might well lead to their use, with intolerable destruction as the result. Indeed, even the existence of the idea of nuclear weapons—more specifically, the ability of many states to make them—is enough to create an existential deterrent effect against large-scale conflicts of all kinds. That is not to say that this effect would necessarily always be sufficient to prevent conflict in the future, any more than it has always been in the past. But it could provide a part of the assurance required, in an international system much different than today's, that all-out wars are unlikely to occur.



If only the core function of nuclear weapons retains validity, fundamental changes in the nuclear force structures and operational practices of the major nuclear powers become both possible and desirable. Accordingly, the committee has concluded that the United States should pursue a two-part program of change in its nuclear weapons policies.

  • The first part of the program is a near and midterm set of force reductions—together with accompanying changes in nuclear operations and declaratory policies and with measures to increase the security of nuclear weapons and fissile materials worldwide—to diminish further confrontational and potentially destabilizing aspects of force postures, to reduce the risks of erroneous, unauthorized, or accidental nuclear-weapons use, and to help curb the threat of further nuclear proliferation. In their early phases these measures are largely bilateral ones between the United States and Russia, and close cooperation between the two countries is essential for success.
  • The second part of the program is a long-term effort to foster international conditions in which the possession of nuclear weapons would no longer be seen as necessary or legitimate for the preservation of national and global security.
Nuclear force reductions and changes in nuclear operations would increase U.S. and global security in important ways.
  • First, reducing U.S. and Russian nuclear forces and revising operations for the mission of fulfilling only the core function will decrease the continuing risk of accidental, erroneous, or unauthorized use of nuclear weapons for several reasons. Smaller arsenals will be easier to safeguard and protect from accident, theft, and unauthorized use, not only by virtue of reduced numbers of weapons to monitor at a smaller number of sites but also by permitting retention of only those weapons with the most modern safety and security features. Reducing alert rates, decreasing capacities to use nuclear weapons quickly and with little warning, abandoning plans for the rapid use of nuclear weapons, and deploying cooperative measures to assure states that forces are not being readied for attack should reduce the probability and consequences of erroneous nuclear weapons use—for example, on false warning of attack. (Of course it is extremely important to take care that reductions in deployed nuclear warheads—and dismantlement of the warheads made surplus as a result—do not lead to countervailing increases in the dangers of theft and unauthorized use as a consequence of inattention to the challenges of safe storage of these weapons and the nuclear materials removed from them.)
  • Second, further reductions will bolster the nuclear nonproliferation regime. U.S.Russian nuclear arms reductions will not in themselves dissuade a state bent on acquiring nuclear weapons; today's undeclared nuclear powers and would-be proliferators are driven above all by regional security concerns. In such cases, the denial of material and technical resources and a combination of political and economic incentives and disincentives provide the greatest leverage. But U.S. and Russian progress in arms reductions helps shore up global support for anti-proliferation measures; and lack of such progress can strengthen the influence of those arguing for nuclear weapons acquisition in countries where this is under internal debate.
  • Third, continued actions by the United States and Russia to reduce their nuclear arsenals—and the roles and missions assigned to those arsenals—will help persuade the other declared and undeclared nuclear weapons states to join the arms control process. At planned START II levels, for example, under which it is estimated that the United States and Russia each would retain a total of about 10,000 nuclear warheads, deployed and in reserve, the other nuclear powers have little motivation to submit their much smaller arsenals to any form of control.


The program that the committee recommends would shift the focus of U.S. nuclear policy. While preserving the core function of deterring nuclear aggression, nuclear forces would be reduced, their roles would be more narrowly defined, and increased emphasis would be placed on achieving higher standards of operational safety.

Building on past nuclear arms control agreements and the anticipated START III agreement, future bilateral U.S.Russian negotiations should center on specific means to achieve these goals. The first step is to encourage the Russian Duma's ratification of START II by beginning now to discuss a START III agreement limiting the number of deployed strategic warheads to about 2,000 on each side.

Establishing progressive constraints on nuclear operations is equally urgent; additional efforts should be pursued in parallel with, but not linked to, discussions of a START III agreement. Such constraints would include programs to reduce alert levels further and progressively to reorient nuclear doctrine away from the requirement to plan for rapid, massive response. Limits on ballistic missile defenses consistent with the Anti-Ballistic Missile (ABM) Treaty would be maintained.

A continuing high priority effort is also needed to improve the protection of nuclear weapons and fissile materials in Russia. Joint U.S.Russian work along these lines, which has been going on since 1991 under the Nunn-Lugar Cooperative Threat Reduction Program, complements and strengthens arms reductions and other changes in nuclear policies. (Because this committee and other NRC committees have recently offered detailed analysis and recommendations on this subject in other reports, the committee does not treat it in detail here.)

During the Cold War, reducing the risk of a surprise attack appeared to be more important than the risks generated by maintaining nuclear forces in a continuous state of alert. With the end of that era, the opposite view is now more credible. This has important implications for U.S. nuclear policy and calls for dramatically reduced alert levels. Elimination of continuous-alert practices should be pursued as a principal goal in parallel with, but not linked to, START III. As a related confidence-building measure, the United States and Russia should adopt cooperative practices to assure each other that they are not preparing for a nuclear attack.

With the Cold War over, planning to retaliate massively against a nuclear attack is not the appropriate basis for making responsible decisions regarding the actual use of nuclear weapons. Operational doctrine regarding the magnitude and timing of any actual retaliation in response to a nuclear attack should be revised. The United States should adopt a strategy that would permit much more selective targeting options and that would be based neither on predetermined prompt attacks on counterforce targets nor on automatic destruction of cities. The presumption instead would be that nuclear weapons, if they were ever to be used, would be employed against targets that would be designated in response to immediate circumstances—in the smallest possible numbers. Some changes in this direction have begun, but the move to a more flexible planning system should be accelerated.

Together, positive and negative security assurances and guarantees have been a useful policy tool to ensure that friends and allies of the United States are not penalized by foregoing nuclear weapons. The United States could do more, however, to make negative security assurances and guarantees serve nonproliferation interests. Most important, the United States should adopt no-first-use of nuclear weapons as its declaratory policy at an early date. Changing to a no-first-use policy will, of course, require consultation with allies to reassure them that the United States will meet, by non-nuclear means, its obligations to come to their aid in the event of a non-nuclear attack on them.

Efforts to ban nuclear weapons from specific regions or environments strengthened nonproliferation in the past and helped to limit the perceived utility of nuclear weapons. The United States should continue to support these agreements and sign them without reservations that undermine their basic purpose, consistent with the unequivocal no-first-use policy recommended above. A new nuclear weapon free zone in Central Europe would, for example, offer immediate security advantages to Russia as well as NATO.

The committee has concluded that the changed international security environment makes possible further reductions in nuclear armaments. After the reductions envisioned in a START III accord, reduction to about 1,000 total warheads each for the United States and Russia would be a logical next step. (All nuclear warheads—regardless of type, function, stage of assembly, associated delivery system, or basing mode—would then be included in the negotiated limits.) A force of this size could effectively maintain the core function against the most challenging potential U.S. adversaries under any credible circumstances. This reduction process must ensure stability at each rung of the ladder, requiring survivable nuclear forces not at risk from a first strike.

Verifying limits on total nuclear warheads is substantially more difficult than verifying limits on their delivery vehicles. Verifying numbers of non-deployed and non-strategic warheads, in particular, would require transparency measures regarding the production, storage, and dismantling of nuclear warheads, as well as a mechanism for exchanging and verifying information about the location and status of warheads. Since nuclear weapons can be small and portable and not easily detectable by technical means, however, a regime that would provide high confidence of locating a small number of hidden warheads would be extremely difficult to achieve. Even an imperfect verification regime would greatly reduce the uncertainties in present U.S. estimates of the number of Russian warheads.

Fulfilling the goals of current arms control initiatives and successfully providing for much deeper reductions will also require improved standards of accounting, transparency, and physical security for fissile materials. Efforts to control fissile materials must address not only the problems presented by military stockpiles but also by civilian use of such materials, in particular plutonium produced by reprocessing. A fissile material cutoff would be a significant nonproliferation measure and should continue to be strongly supported by the United States.

The ABM treaty will continue to play a crucial role in a world in which the numbers of nuclear weapons are drastically reduced and the role of nuclear weapons is restricted to the core function. Maintaining and enhancing its integrity in light of changes in offensive nuclear capabilities will require periodic evaluation. The focus of the U.S. ballistic missile defense research and development program should be to field a mobile system capable of defending relatively small areas against projected theater ballistic missile threats, which the committee believes will remain limited to a range of roughly 1,000 kilometers for some time.

The achievement of U.S.Russian reductions to a mutually agreed level of about 1,000 total warheads each should not represent the final level for nuclear arms reductions. There will still be powerful reasons to continue down to a level of a few hundred nuclear warheads on each side, with the other three declared nuclear powers at lower levels, or with no remaining nuclear forces.

The small numbers of nuclear weapons presumably now held by the undeclared nuclear states—India, Israel, and Pakistan—would become a key issue when the United States and Russia, as well as the other declared nuclear powers, consider reductions to very small numbers of warheads. High priority should be given to diplomatic strategies tailored to the security perceptions of each state in order to freeze or reduce and, if possible, eliminate these undeclared programs in parallel with the reduction programs of the nuclear powers.

The committee's analysis does not assume a fundamental change in the nature of international relations in order to achieve these low levels of nuclear arms. It does assume unprecedented cooperation and transparency among all classes of nuclear powers on the specific issue of nuclear arms reductions. A few hundred nuclear weapons would be sufficient to deter nuclear attack through their potential to destroy essential elements of the society of any possible attacker. These remaining nuclear forces would have to be survivable and their command-and-control structure adequately redundant and robust; and widespread and effective national ballistic missile defenses must be absent. The operational posture of the much smaller forces must be designed for deliberate response rather than reaction in a matter of minutes.



The end of the Cold War has created conditions that open the possibility for serious consideration of proposals to prohibit the possession of nuclear weapons. It is not clear today how or when this could be achieved; what is clear is that comprehensive nuclear disarmament should be undertaken only in circumstances such that, on balance, it would enhance the security of the United States and the rest of the world.

The committee uses the word "prohibit" rather than "eliminate" or "abolish" because the world can never truly be free from the potential reappearance of nuclear weapons and their effects on international politics. Even the most effective verification system that can be envisioned would not produce complete confidence that a small number of nuclear weapons had not been hidden or fabricated in secret. More fundamentally, the knowledge of how to build nuclear weapons cannot be erased from the human mind. Even if every nuclear warhead were destroyed, the current nuclear weapons states, and a growing number of other technologically advanced states, would be able to build nuclear weapons within a few months or few years of a national decision to do so.

A durable prohibition on nuclear weapons would have three main benefits:

  • It would virtually eliminate the possibility of use—whether authorized and deliberate or not—of nuclear weapons by states now possessing them. Viewed in light of the possibility of reconstitution of such arsenals in a crisis, prohibition can be seen as extending the dealerting measures recommended in the near-term part of the program—that is, increasing the time required to ready nuclear weapons for use from hours or days to months or years.
  • It would reduce the likelihood that additional states will acquire nuclear weapons. Although the Nuclear Nonproliferation Treaty currently enjoys almost universal adherence, the nuclear weapons states cannot be confident of maintaining indefinitely a regime in which they proclaim nuclear weapons essential to their security while denying all others the right to possess them.
  • It would deal decisively with the uncertain moral and legal status of nuclear weapons, as underlined by the recent advisory opinion of the International Court of Justice.
Nuclear disarmament poses risks as well as benefits, however:
  • The prohibition on nuclear weapons might break down via cheating or overt withdrawal from the disarmament regime. To reduce these risks, a disarmament regime would have to be built within a larger international security system that would be capable not only of deterring or punishing the acquisition or use of nuclear weapons but also of responding to major aggression.
  • Comprehensive nuclear disarmament could remove the moderating effect that nuclear weapons appear to have had on the behavior of states. The nuclear era represents the longest period without war among the major powers since the emergence of the modern nation state in the sixteenth century. Thus, it is argued that, if the major powers believed the risk of nuclear war had been eliminated, they might initiate or intensify conflicts that might otherwise have been avoided or limited. But there have been, and continue to be, profound changes in the structure of the international order that are acting to reduce the probability of major war independent of nuclear deterrence. Moreover, even if all nuclear weapons were eliminated, the inherent capacities to rebuild them could act as a deterrent to the outbreak of major wars.
If the preconditions for agreed prohibition of nuclear weapons are met, however, the committee believes that a path to eventual prohibition can be found. One possible path for managing the transition to comprehensive nuclear disarmament would involve having an international agency assume joint or full custody of the arsenals remaining during the transition to prohibition. Alternatively, nations might find it preferable to bypass the intermediate step involving an international agency and proceed directly to negotiations to prohibit nuclear weapons either globally in a single agreement or in steps involving successive expansions in the number and geographical scope of nuclear weapon free zones.

It will not be easy to achieve the conditions necessary to make a durable global prohibition on the possession of nuclear weapons both desirable and feasible. Complete nuclear disarmament will require continued evolution of the international system toward collective action, transparency, and the rule of law; a comprehensive system of verification, which itself will require an unprecedented degree of cooperation and transparency; and safeguards to protect against the possibility of cheating or rapid breakout. As difficult as this may seem today, the process of reducing national nuclear arsenals to a few hundred warheads would lay much of the necessary groundwork. For example, the stringent verification requirements of an agreement on very low levels of nuclear weapons and fissile materials might by then have led to some new or expanded international agency with vigorous powers of inspection. The committee has concluded that the potential benefits of a global prohibition of nuclear weapons are so attractive relative to the attendant risks that increased attention is now warranted to studying and fostering the conditions that would have to be met to make prohibition desirable and feasible.

In any case, the regime of progressive constraints constituting the committee's proposed near to midterm program makes good sense in its own right—as a prescription for reducing nuclear dangers without adverse impact on other U.S. security interests—regardless of one's view of the desirability and feasibility of ultimately moving to prohibition.


CISAC Study Panel

William F. Burns, study chair, Major General (U.S. Army, Retired)

John P. Holdren, committee chair, Professor, Center for Science and International Affairs, John F. Kennedy School of Government, Harvard University

John D. Steinbruner, committee vice chair, Senior Fellow, Foreign Policy Studies Program, The Brookings Institution

George Lee Butler, Vice President, Peter Kiewit Sons, Inc.

Paul M. Doty, Director Emeritus, Center for Science and International Affairs, Harvard University

Steve Fetter, Associate Professor, School of Public Affairs, University of Maryland, College Park

Alexander H. Flax, President Emeritus, Institute for Defense Analyses and Senior Fellow, National Academy of Engineering

Richard L. Garwin, Fellow Emeritus, Thomas H. Watson Research Center, IBM Corporation

Rose Gottemoeller, Deputy Director, International Institute for Strategic Studies

Spurgeon M. Keeny, Jr., President, Arms Control Association

Matthew Meselson, Professor, Department of Molecular Biology and Cellular Biology, Harvard University

Wolfgang K. H. Panofsky, Professor and Director Emeritus, Stanford Linear Accelerator Center, Stanford University

C. Kumar N. Patel, Vice Chancellor—Research, University of California at Los Angeles

Jonathan D. Pollack, Senior Advisor for International Policy, The RAND Corporation

Robert H. Wertheim, Rear Admiral (U.S. Navy, Retired)

Jo L. Husbands, study director, Committee on International Security and Arms Control, National Academy of Sciences

Copies of The Future of U.S. Nuclear Weapons Policy are available for $15.00 (plus $4 for shipping and handling) from the National Academy of Sciences, 2101 Constitution Avenue, NW, Washington, DC, 20148 or phone 202-334-2138 or 1-800-624-6242.