Missile Defense: The Sequel

Since the beginning of warfare, humans have sought defenses against offensive weapons. Not surprisingly, then, the deployment of nuclear-armed missiles by the United States and the Soviet Union early in the Cold War prompted each to begin building missile defenses to protect themselves against these extremely destructive weapons.

What is perhaps surprising is that both countries soon recognized that this undertaking would be destabilizing and pointless and agreed in the 1972 Anti-Ballistic Missile (ABM) Treaty not to defend their countries against each other’s ballistic missiles. The two superpowers both based their nuclear policies on the notion of deterrence-that maintaining the ability to launch a nuclear counterattack that would inflict massive destruction on the other side was necessary to ensure that the other country would not attack first.

Missile defense could weaken or even negate the retaliatory capability of the other side, since a retaliatory attack would be small and uncoordinated. Thus, it was believed, their deployment would provoke the other country to take measures to preserve its deterrent. One straightforward but dangerous response to a defensive system would be to build up the size of the offensive arsenal. Another would be to adopt a policy of “launch on warning,” which would permit missiles to be launched rapidly when sensors detected an incoming attack. This policy would prevent a country from being disarmed by a first strike but would increase the risk of accidental launch since the decision to launch would need to be made quickly.

Both responses would lead to a more dangerous world, while making the quest for effective defenses futile. It was to avoid this destabilizing dynamic that the United States and the Soviet Union signed the ABM Treaty.

In the mid-1980s, President Reagan, rejecting the logic of the ABM Treaty, launched the Strategic Defense Initiative. Under this program, often referred to as “Star Wars,” the Pentagon focused on advanced technologies such as space-based lasers to develop a multi-layered defense of the United States against a large-scale Soviet attack. The nation spent tens of billions of dollars on R&D. The program eventually lost political support, however, because opponents successfully argued that any advances in technology were irrelevant-that Soviet responses would still prevent defenses from being effective-and that building them would diminish, rather than enhance, U.S. security. The logic of the ABM Treaty ultimately prevailed.

But the United States is again moving toward deploying defenses against attacks by ballistic missiles. Iraq’s use of conventionally armed Scud missiles against Israel and Saudi Arabia in the 1991 Gulf War raised concern about the proliferation of ballistic missiles, and U.S. efforts shifted away from a system that would shield the entire country from large-scale Soviet attack toward “theater” defenses, designed to protect U.S. troops and allies abroad from shorter-range missiles. But after taking control of Congress in the 1994 election, Republicans put deployment of “national” defenses-this time intended to counter limited missile attacks against U.S. territory-back on the agenda as well.

Proponents of the new missile defense systems argue that the risks to national security of building defenses are lower than in the past, and the benefits higher. Most fundamentally, some argue, the United States and Russia are no longer enemies; Moscow would not be threatened by U.S. missile defenses and thus would not respond in ways that would hurt U.S. security. Other proponents argue that even if U.S. missile defenses did worry Russia, that economically strapped country could not afford an arms buildup in response.

Still other proponents note that today’s missile threats are different: their concern is no longer a deliberate large-scale Soviet nuclear attack but rather an accidental or unauthorized launch of missiles by Russia, an attack by China, or possibly threats from Third World countries that acquire long-range missiles. Guarding against these attacks, they argue, would require only limited national defenses that would not threaten Russia’s much larger nuclear deterrent. Moreover, this argument continues, U.S. deployment of theater defenses should not concern Russia since these systems would not be intended for use against Russian missiles.

Missile-defense advocates argue that the benefits of deployment are higher than during the Cold War because there is a real and increasing missile threat that it is possible to defend against. They argue that missile-defense systems are far more likely to work against the shorter-range missiles, and against attacks from a small number of long-range missiles, than against a massive assault by sophisticated, long-range missiles-the threat that motivated previous missile-defense programs.

Both political parties have, to varying degrees, bought into the idea that missile defense of some kind is a practical and wise idea; the United States has for the past few years been spending roughly $3 billion a year to study and develop such systems. While this total is down from the peak of some $4.5 billion a year at the height of the Strategic Defense Initiative in the late 1980s, it is far from clear that even this level of effort makes much sense. Thus far, this money has bought only research, development, and testing; building, deploying, and maintaining the systems would require much larger budgets.

Despite the breakup of the Soviet Union, things have not changed quite so much as missile-defense advocates suggest. Proponents overstate the missile threat and the ability of defenses to address what threat exists. Perhaps most importantly, they largely ignore the potential security costs of deploying many of the defenses being developed.

Political Battles

The Clinton administration and congressional Republicans have clashed over the timing of deploying a national missile defense system. Last spring, the Defend America Act, introduced in both houses of Congress, mandated deployment by 2003 of a “highly effective” and “affordable” system that would protect all 50 states from “limited, unauthorized, or accidental” attacks. But when the Congressional Budget Office estimated that such a system would cost $3160 billion to build and an additional $24 billion annually to maintain, the House Republicans dropped their legislation out of concern that their party’s budget hawks would not vote for it.

The Republicans have written the National Missile Defense Act of 1997 with an eye toward getting a more favorable cost estimate: they have eliminated the requirement that the system be “highly effective,” and specify now only that the system be able to deal with very small-scale attacks. Although the requirements remain classified, the system reportedly must now defend against attacks of no more than five to twenty “simple” warheads-that is, warheads that do not incorporate any countermeasures that would help them evade detection and interception.

This experience points to the difficult task that national missile defense advocates face in defining a system that is both politically attractive (it must be seen as necessary and effective) and politically feasible (it must be affordable). The specifics of these defense systems have been left vague precisely because it is difficult to satisfy both requirements simultaneously. Right now no potentially hostile country other than Russia or China has long-range missiles that can hit the United States. Therefore, it has been politically useful to require the system to defend against unauthorized and accidental attacks by Russia or China-these, at least, are threats that exist today. Contrary to common perception, however, “unauthorized” and “accidental” do not necessarily mean “small.” Depending on where in the chain of command the control breaks down, such an attack could be quite large. Some argue that the most feasible unauthorized attack would come from a Russian submarine, which carries some 200 nuclear warheads. Yet, defending against an attack of this size requires a much larger and more expensive system than one designed to swat down a few errant missiles.

The Clinton administration holds that there is no immediate threat and that deploying a system before it is needed only guarantees that the technology will be outdated by the time a threat develops. Instead, under its “3 + 3” plan, the administration intends to develop within three years (by 2000) a system that could be deployed in an additional three years (by 2003) if a threat emerges. If in 2000 no such threat is deemed to exist, development will continue. That way, an up-to-date system will always be three years from deployment. President Clinton thus far has prevailed: he vetoed the fiscal 1996 defense authorization bill in large part because the bill’s insistence on missile defense would, he said, put the United States “on a collision course with the ABM Treaty.” Since this year’s missile-defense legislation still mandates deployment by 2003, President Clinton is expected to veto it if it is passed.

Although Clinton has won each battle over deployment of national missile defenses, the Republicans may be winning the war. They have clearly set the terms of the debate, and in trying to undercut their plan for mandated deployment, Clinton’s 3+3 plan will move the United States much closer to deployment of national missile defenses than it has ever been.

By remaining vague on the details of its 3+3 plan, the administration has been able to avoid the question of compliance with the ABM Treaty. Although Clinton cited the treaty as justification for his veto of the fiscal 1996 authorization bill, deployment of the 3 + 3 system would almost certainly violate the treaty as well. The bottom line is that the ABM Treaty forbids nationwide defenses, and building a system that covers only part of the United States would be politically unacceptable. Any defense system that complies with the ABM treaty would leave unprotected large parts of both coasts, as well as Alaska and Hawaii.

Providing coverage of the entire United States against even limited attacks would require either that the United States and Russia agree to modify the ABM Treaty or that the United States withdraw from it. The first prospect is unlikely, and the second unjustified. Russia has no incentive to agree to a treaty modification to accommodate U.S. national defenses. Even a limited defensive system would put into place the sensors and other infrastructure needed to allow a relatively rapid expansion to a larger-scale system. And withdrawing from the treaty is permitted only if “extraordinary events” jeopardize U.S. “supreme interests”-a position that is difficult to argue.

Opening the Curtains on Theater Defense

Roughly two-thirds of the U.S. missile-defense budget is earmarked for theater rather than national missile defenses. The ABM Treaty allows theater defenses as long as these systems cannot also intercept long-range strategic missiles. The United States is now developing several kinds of theater systems, some that have run into compliance problems with the treaty.

Low-altitude defenses are designed to shoot down short-range missiles-those with ranges up to 6001000 kilometers, which travel at 23 kilometers per second-well within the atmosphere. Such defenses gained fame during the Gulf War when the United States claimed its Patriot system successfully shot down Iraqi Scud missiles-a claim now generally discredited.

Development is continuing on a significantly upgraded version of the Patriot. Other low-altitude defense systems include Navy Area defense, which will be based at sea on Aegis cruisers and destroyers; the Medium Extended Air Defense System, being developed jointly with European allies; and the Arrow program, which Israel is developing with U.S. funding.

These defenses are clearly permitted by the ABM Treaty: they would be unable to intercept 10,000-km range Russian strategic missiles, which reenter at much higher speeds of 7 kilometers per second. Moreover, it would be infeasible to use these systems for national defense because hundreds would be required to cover the entire United States.

The Pentagon is developing other theater defense systems, however, whose treaty compliance is in serious question. These high-altitude systems are designed to defend large areas against missiles with ranges up to 3,500 kilometers and that move at up to 5 kilometers per second, by intercepting them above or in the upper layers of the atmosphere. The United States is developing two such high-altitude systems-the Army’s ground-based and air-transportable system known as THAAD, for Theater High Altitude Area Defense, and the Navy Theater Wide system, to be deployed at sea on Aegis ships. The Pentagon plans to buy some 1,200 THAAD interceptors at an estimated cost of $1015 billion. A prototype system would be deployed around the turn of the century, with full-scale deployment beginning in 2004. A few years later, the Navy Theater Wide system would be deployed, with 650 interceptors on 20 or more ships.

Neither system has done well in tests, however, so these schedules may be optimistic. As of March, THAAD had failed all four of its intercept tests, leading Pentagon officials to suggest a major restructuring of the program. Navy Theater Wide is not as far along in its test series, but as of early this year the system had failed both of its intercept tests.

Some proponents incorrectly argue that the two high-altitude theater defenses could not be used as part of a national defense. Although not designed to protect U.S. territory, these high-altitude defenses are designed to be mobile and could readily be moved to the United States in a time of crisis. Because these systems intercept outside or high in the atmosphere, where the missile will not be maneuvering, the defense system can accurately predict the trajectory the missile will follow. Thus if these defenses perform as intended against missiles with speeds of 5 kilometers per second, then they would also be capable of intercepting strategic-range missiles traveling at 7 kilometers per second.

Moreover, if advanced sensors now under development are used, the ground area covered by these systems could be large enough to permit a nationwide defense. These sensors would provide early detection of missile attack, allowing interceptors to be launched sooner. The U.S. early-warning radars, to be upgraded as part of the national missile defense program, could allow 6 or 7 Navy Theater Wide batteries to cover the entire United States; indeed, this is the basis for a limited national defense proposed by the Heritage Foundation and others. Even better sensor data would be available if the United States deploys the Space and Missile Tracking System currently being developed for use by both national and theater defenses. This program, formerly known as “Brilliant Eyes,” would use about two dozen satellites in low earth orbit. The Clinton administration wants deployment by 2006, but Congress is pushing for 2003. If such a network of space-based sensors were deployed, as few as ten THAAD or three to four Navy Theater Wide batteries could cover the United States, providing, in effect, a national defense-precisely what the ABM Treaty bans.

Indeed, early in THAAD’s development, a Pentagon study concluded that the system would violate the Treaty. The Clinton administration therefore began negotiating with Russia in November 1993 to modify the treaty to permit testing and deployment of both THAAD and Navy Theater Wide. Russia balked at the proposed changes, however, and the negotiations were deadlocked until very recently. In response to this lack of progress, the United States stated that it nonetheless intended to proceed with both THAAD and Navy Theater Wide, claiming that both would be treaty-compliant. During the March summit with President Clinton, President Yeltsin apparently dropped essentially all of Russia’s negotiating positions, including restrictions on space-based sensors. This agreement, if it stands, would thus permit deployment of defenses with significant strategic capabilities, weakening the treaty.

Assessing the Benefits of Defense

Making rational decisions on U.S. missile-defense policy requires weighing the potential security benefits and costs for both national and theater missile defenses. The benefits will depend on both the need for such systems and their likely effectiveness.

Proponents are seeking national missile defenses to protect U.S. territory against three possible threats: accidental or unauthorized launches of long-range Russian or Chinese missiles; deliberate attacks from China; and potential future attacks from other, hostile countries.

The possibility of an unauthorized or accidental launch of nuclear missiles is real. But missile defenses are not the best safeguard. In fact, deployment of national missile defenses could increase this threat, if it prompted Russia or China to rely more on launch-on-warning strategies or increase their alert rates. Other, cooperative measures would be more effective and less expensive. The nuclear powers could, for example, agree to install mechanisms to destroy errant missiles after launch, or to store warheads separately from missiles.

This approach has an added benefit: depending on where in the chain of command an accidental or unauthorized launch occurs, such an attack could be so large as to overwhelm a limited defense. Destroy-after-launch mechanisms would be able to address any size launch, and removal of warheads from missiles would preclude such a launch in the first place. If the United States is interested in resolving this concern, then working with Russia and China would be the best approach since it is clearly in their interests to prevent such launches, too.

The threat of a deliberate Chinese attack is very small, given the certainty of U.S. retaliation. Moreover, to retain its deterrent against the United States, China would take steps to prevent U.S. national defenses from being effective against its missiles.

The “rogue nation” threat has been exaggerated. Other than Russia and China, no country considered hostile to the United States has missiles capable of coming even close to U.S. territory.

There are five countries with missiles that are typically considered threats to U.S. interests: Iran, Iraq, Libya, North Korea, and Syria. Iraq, however, is not a realistic threat: its missile program is being dismantled under the terms of the UN resolution that ended the Gulf War, and long-term monitoring is being set up to ensure that Iraq will not be able to resume this program. All missiles deployed by the other four countries are either 300-kilometer-range Scud missiles acquired from the Soviet Union or derivatives of these missiles with ranges up to about 600 kilometers-well short of the 5,000-10,000 kilometers any of these countries would need to strike the United States.

Of the four remaining countries, North Korea has the greatest indigenous ability to develop longer-range missiles. However, despite reportedly working on a 1,000 kilometer-range missile-the “Nodong”-since the late 1980s, North Korea has yet to test a missile of this range. Foreign technical assistance could, of course, speed the development of longer-range systems in North Korea or elsewhere. But even with help, developing long-range missiles is a demanding and expensive process. And U.S. satellites would be able to observe missile flight tests, providing clear warning of threatening developments.

The other possible route for a developing country to obtain long-range missiles-acquiring them from one of the few countries that already has them-is highly unlikely. Long-range missiles are typically about 20 meters long and weigh many tens of tons, and are therefore essentially impossible to steal without the knowledge of the authorities. And it would be against Russia’s and China’s self interests to sell long-range missiles, because such sales would prompt severe economic sanctions under an international agreement prohibiting such transfers and because these missiles could be turned against them.

Moreover, even if a developing country did seek to attack the United States with weapons of mass destruction, long-range missiles are probably the least likely method it would choose. U.S. satellites would pinpoint the origin of any missile attack, so the threat of quick retaliation will be a powerful deterrent. Meanwhile, other methods of delivery, such as those used in the World Trade Center and Oklahoma City bombings and in the Tokyo subway gas attack, are relatively cheap, require only low technology, can be used clandestinely, and can be accurately targeted to make the most of a limited arsenal.

Leaving aside the question of the future threat, how effective might limited national missile defenses be if a threat did emerge?

The assumption that underlies current plans for national defenses-that incoming missiles would use no countermeasures- is unjustified. Any country that could develop a long-range missile could also deploy a variety of simple countermeasures that would make the job of the defense much more difficult if not impossible. Any missile delivering chemical or biological weapons can simply overwhelm the defense by using a large number of small warheads, called submunitions. A nuclear-armed missile can take advantage of the fact that interceptors for national missile defense systems are designed to work at high altitudes where, because of the thin atmosphere, objects of different shapes and mass travel at the same speed. This makes it possible to use lightweight decoys that simulate the warhead to create a large number of false targets or to hide the warhead in a large balloon so the interceptor would not know where to aim. Despite decades of work, the United States has not found a solution to the problem of such countermeasures.

Other ways to address the possible proliferation of long-range missiles are likely to be more effective and cheaper than missile defenses. Because U.S. satellites would provide warning of long-range missile development and deployment, the United States could destroy such missiles preemptively. More important, the United States has options available that could prevent a threat from materializing in the first place. Some diplomats believe, for example, that North Korea may be willing to bargain away its entire missile program in exchange for economic assistance, much as it did with its nuclear program.

The analysis for theater missile defenses is different. The short-range missiles possessed by Iran, Libya, North Korea, and Syria do represent a possible threat to U.S. troops or allies abroad. These missiles are armed with conventional warheads and possibly, in some cases, chemical or biological weapons. However, the 1,000-kilometer range Nodong missile reportedly under development by North Korea is essentially the longest range missile achievable using Scud technology; any theater missiles the United States will face in at least the medium-term future will have shorter reach. High-altitude defenses are not needed against this threat; low-altitude theater missile defenses are appropriate for this purpose.

Missile-defense proponents claim that short-range missiles will be relatively easy to defend against, but this may not be so. As with national defenses, the effectiveness of theater defenses will depend heavily on the countermeasures that the attacker uses. For example, the Patriot succeeded in all 17 of its intercept tests prior to the Gulf War, yet apparently shot down at most one, and probably zero, Iraqi missiles. The Scuds broke into several pieces as they reentered the atmosphere, inadvertently creating decoys and causing the warhead to tumble in unpredictable ways.

Incorporating countermeasures into any new theater missiles produced would be easier than building the missile itself, and retrofitting old missiles with simple and effective countermeasures would not be difficult. Both low- and high-altitude theater defenses would be defeated by submunitions. High-altitude defenses would also be susceptible to the same types of simple countermeasures as the national missile defense systems, thus shrinking the area covered by the defense. As a result, high-altitude defenses would provide little, if any, defensive capabilities beyond those provided by low-altitude defenses.

How Defenses Lower Security

Even though the United States and Russia are scaling back their nuclear forces, the two countries still base their military relationship on nuclear deterrence. Both countries still rely primarily on nuclear-armed ballistic missiles to provide this deterrence. Moreover, there is no evidence that either country plans to move away from nuclear deterrence, despite growing pressure from the world’s non-nuclear nations for a commitment to nuclear disarmament. Russia is equally wedded to nuclear deterrence and views nuclear weapons as key to its superpower status and as a counterweight to its deteriorating conventional military strength.

This continued commitment to deterrence means that to whatever extent defenses threaten or appear to threaten deterrent forces, the same old problems will arise. Russia and China see as a fundamental security issue the need to preserve their ability to inflict a punishing nuclear retaliatory blow. It is therefore unlikely that these countries would sit idly by while the United States deployed a defense that they believed might render a retaliatory strike ineffective.

Russia would probably endow its missiles with countermeasures to protect them against U.S. missile defenses. A reliance on countermeasures, however, will introduce new uncertainties in Russian military planning. Russian leaders may find it implausible that the United States would be spending tens of billions of dollars on defenses that would be so easy to defeat. Thus, even if scientists and engineers are confident that their countermeasures would work, it is not clear they would be able to prevent Russia’s military and political leaders from responding in other, destabilizing ways as well.

While it can ill afford an arms buildup in response to U.S. missile defenses, Russia has other, less costly, options that could be equally problematic. Russia could, for example, increase its reliance on a policy of launch-on-warning or increase its alert rate, raising the chance of accidental and unauthorized launches. Moreover, Russia could simply refuse to cut its nuclear arsenal further. When Russia ratified the first Strategic Arms Reduction Treaty (START I), which cuts deployed forces to some 8,000 warheads, it made its fulfillment of the agreement contingent on continued U.S. compliance with the ABM Treaty. The START II agreement, which would cut deployed forces to 3,500 warheads, was ratified by the U.S. Senate but has run into deep political problems in the Duma (parliament) in part because of U.S. plans for missile defense. If Russia does ratify START II, the Duma will certainly link fulfillment of the treaty to preservation of the ABM Treaty.

Even if Russia were not concerned about U.S. missile defenses at START II or III force levels, defenses would almost certainly be a significant barrier to much deeper cuts in Russian (and hence U.S.) nuclear forces. As arsenals shrink, deterrent forces will become more vulnerable to even limited defensive deployments. Thus, those who argue that a limited U.S. national missile defense would entail no security costs since it would not threaten Russia’s large arsenal ignore the fact that U.S. security is best served by irreversible cuts in nuclear weapons to very low numbers-tens or perhaps 100. (Of course, some policymakers want to retain a large U.S. nuclear arsenal indefinitely and are thus unconcerned that missile defenses could preclude deep cuts.)

Even if Russia has finally agreed to a treaty modification permitting high-altitude defenses, deployment of such defenses could still stand in the way of deep cuts. That Russia has serious concerns about the strategic capability of these defenses is clear from the past three years of negotiations, and these concerns have presumably not evaporated despite Yeltsin’s concessions. Indeed, Russian agreement may only signify that it is comfortable with such defenses at START III force levels, and that it does not intend to cut significantly further.

The prospect of missile defenses might also cause Russia to keep open the option of expanding its arsenal in the future by refusing to agree on controls on the fissile material that nuclear weapons are made of. Russia might be reluctant to declare surplus much of its large existing stocks, for example. That would run counter to U.S. efforts to render its surplus fissile material difficult to re-use or steal, and its attempts to convince Russia to do the same.

Considering China

U.S. security interests also dictate that the United States consider Chinese reactions to its missile defense plans. Although not a party to the ABM Treaty, China bases its nuclear planning in part on the treaty and has historically been concerned about U.S. and Soviet missile defense programs. China is believed to have several hundred nuclear weapons but perhaps only about two dozen are able to reach the United States. Even a limited national missile defense system, therefore, could undermine or negate the Chinese deterrent.

China has expressed concern about high-altitude theater defenses too. Sha Zukang, China’s ambassador to the Conference on Disarmament, noted in a statement to the U.N. General Assembly last October that such systems will “possess the capability to intercept strategic missiles” and that their development thus would dampen China’s “enthusiasm to participate in the global process of arms control and disarmament.” Moreover, U.S. deployment of high-altitude theater defenses would open the door for Russia to do the same. Such a move could threaten the bulk of China’s missile force, which have ranges of less than 3,500 kilometers and constitute the backbone of its deterrent against Russia.

China also worries about possible transfers of U.S. theater defenses to neighboring countries and U.S. deployment of sea-based systems in the region. The United States has tried to enlist Japan as a partner to help fund development of THAAD. China views Japan as a latent nuclear power, and given the historical enmity between the two countries, is uncomfortable with the prospect of a potential combination of Japanese nuclear weapons and missile defenses. Japan has recently all but opted out of the THAAD project, however, partly because the cost is too high and partly to minimize tensions with China.

China is also upset by U.S. plans to sell Patriot defenses to Taiwan in response to the intimidating missile tests China conducted off Taiwan’s coast prior to Taiwan’s elections last year. Because these are only low-altitude defenses, however, such a sale is unlikely to affect China’s nuclear or arms-control policies.

Given its concerns, China could react to U.S. missile defenses in a number of ways that could reduce U.S. security and hinder further efforts to control and eliminate the world’s nuclear arsenals. To preserve its nuclear deterrent, China, like Russia, could build up its nuclear forces or adopt a launch-on-warning posture. China could also decide to keep open the option of building up by refusing constraints on fissile material production. The United States is seeking an international treaty prohibiting further production of fissile material for nuclear weapons, partly as a way to place some controls on the nuclear-weapon programs of the undeclared nuclear states-India, Israel, and Pakistan. China’s agreement to this treaty is essential, both because of its own nuclear arsenal and because its participation will be needed to gain that of India and, in turn, Pakistan.

If and when the United States and Russia continue to cut their deployed nuclear weapons to roughly the numbers held by the smaller nuclear powers-China, Britain, and France-it will become necessary to include these countries in negotiating deeper cuts. But in response to U.S. defenses, China could hamstring this process by refusing to accept limits on its deployed arsenal.

Finally, because both Russia and China are potential suppliers of nuclear and missile technologies to other countries, their participation in international nonproliferation efforts is crucial. But the ill will that missile defense deployments could cause may make both Russia and China less willing to cooperate with the West on restricting transfers of sensitive technology to other countries, or to participate in other nonproliferation initiatives.

Thus the overall result of U.S. deployment of national missile defenses and high-altitude theater defenses could well be that nuclear reductions and other irreversibility measures grind to a halt and that the United States and Russia become locked in at high levels of deployed weapons, while retaining their ability to rapidly build more. The other nuclear weapon states would then refuse to become involved in nuclear arms reductions. Creating such barriers to deep nuclear reductions and disarmament, which the nuclear weapon states are obligated to pursue under the Nuclear Non-Proliferation Treaty (NPT), would become increasingly unacceptable to the 180 non-nuclear-weapon state members of the NPT. Over time, this discontent could weaken the international nonproliferation regime.

These potential costs to U.S. security might be worth risking if the missile threat were greater and defenses were a more effective means of countering this threat. But this is not the case. There is no missile threat from developing countries that justifies national missile defenses, and there may never be. There are more effective means of addressing the problem of accidental and unauthorized launches from Russia and China. No long-range theater missiles justify deployment of high-altitude theater defenses; low-altitude defenses will provide most if not all of the realizable benefits of defenses against existing and likely future theater missiles, and without the attendant security costs.

The desire to defend the United States, its troops, and allies against all threats is understandable. But U.S. policymakers must weigh both the costs and benefits of deploying missile defenses. U.S. security-and indeed international security-will best be served if the United States forgoes national missile defenses and high-altitude theater defenses.n