Table of Contents

U.S. missile defenses, like nuclear forces, come in various forms, with different capabilities, objectives, costs, and reactions from allies and adversaries. The capabilities and footprint of U.S. missile defense have expanded continually over the past twenty years. Today, they have attained a global reach, increased technological capability, priority in defense budgets, and adoption by U.S. allies. (Appendix B contains a record of U.S. missile defense tests for Aegis and Ground-Based Midcourse Defense systems, perhaps the most relevant defensive systems to adversary nuclear postures.) Still, the technical functionality of missile defenses against modern missile forces is unknown. The United States has not used missile defenses against a nuclear-armed adversary. Nor have Israel’s vaunted air defenses been used against advanced cruise or ballistic missiles.

Forward-deployed missile defenses—interceptors based on land and on ships with warning and communications assets—play a role in regional deterrence, defending allies and partners, U.S. forces, and critical military and civilian installations on foreign territory. The United States uses basing arrangements and foreign military sales to encourage interoperability and information-sharing among allies to improve the effectiveness of their missile defenses.1 Missile defenses on and near U.S. territory are supposed to defend the U.S. homeland from ballistic missile attacks of the scale that North Korea might be able to launch. In both scenarios, U.S. missile defense can contribute to defeating and deterring conventionally and nuclear-armed missile attacks, whether targeted at American cities or U.S. nuclear and military forces. Because the focus of this review is nuclear policy, its analysis and recommendations focus on three conundrums that missile defenses could pose to managing and reducing nuclear threats.

U.S. regional missile defense arrangements include theater missile defense systems, such as Patriot and THAAD (Terminal High Altitude Area Defense), that are designed for terminal and “point” defense. These systems are better suited for protecting smaller areas where important military installations and critical infrastructure may be located. Longer-range systems, such as Aegis, also contribute to regional missile defense architectures, operating off the coasts of U.S. allies in Europe and Asia. In Europe, NATO allies host a radar site in Turkey, a command center in Germany, and an Aegis Ashore site where Aegis SM-3 interceptors are deployed on land in Romania with a planned second site in Poland, as part of the European Phased Adaptive Approach.2 In Asia, the United States has deployed THAAD radars and launchers in Guam, Hawaii, and South Korea.3 All of these systems are intended to protect U.S. allies as well as U.S. forces stationed on allied territories.

Notwithstanding the primary missions of deterring and countering North Korean and Iranian missile threats, U.S. military planners and contractors also envision these systems’ potential role in interdicting Russian or Chinese conventional and nuclear attacks on targets in Europe and East Asia. For instance, the 2019 Missile Defense Review (MDR) states that “missile defense is an element of the U.S. effort to counter A2/AD [antiaccess/area denial] strategies that seek to deter or prevent the United States from supporting allies in contested regions,” implicitly suggesting that missile defense will blunt Russian and Chinese attacks associated with their strategies for regional conflicts.4 The November 2020 test of the SM-3 against an ICBM target deepened Russia’s and China’s suspicions that U.S. missile defenses will be directed against them.5 As the presence of Aegis ships and land installations increase, Russia and China may further lose confidence in the efficacy of their ballistic missiles. In 2017, China reacted harshly (including an economic boycott) to the deployment of THAAD radars in South Korea, claiming the system could help target Chinese ICBMs.

These dynamics raise two conundrums at the regional level. First, the United States has insisted that regional defenses intended to deter or block North Korean or Iranian attacks do not pose threats to Russian and Chinese strategic nuclear deterrents. But Moscow and Beijing profess not to believe these statements. To the extent that Russia and/or China add offensive capabilities to counter such defenses, would the benefits of defenses against regional Iranian and/or North Korean missiles outweigh the costs?

Second, the United States also seeks increased capabilities to defend its forward-deployed forces and allies and partners from Russian and Chinese regional missiles. These capabilities are especially important in East Asia, where China has steadily increased its arsenal of short- to medium-range conventionally armed and dual-capable missiles. Here the major conundrum is that it is easier and cheaper for China to add missiles of this range than it is for the United States to add defenses to feasibly counter them. Moreover, kinetic and perhaps cyber capabilities to target Chinese missiles and their command and control systems could intentionally or inadvertently attack (or be perceived to attack) Chinese nuclear command and control. This could exacerbate risks of escalating a regional conventional war into a nuclear one. That concern notwithstanding, such antimissile capabilities also could strengthen deterrence.

The third set of conundrums involves U.S. homeland defenses against ballistic missiles, and the likelihood that they drive Russia and China to increase their arsenals of long-range missiles and warheads. When the United States withdrew from the 1972 Anti-Ballistic Missile (ABM) Treaty in June 2002, the stated reason was the need to develop and deploy systems that could defend the U.S. homeland from attack by future North Korean and Iranian ballistic missiles. This reasoning remains the stated objective of homeland missile defenses. Although Iran still does not possess missiles that could reach the United States, North Korea has tested several types of missiles that could improve its capabilities.6 For its part, to potentially counter this threat, the United States still deploys only a little more than half the number of missile interceptors on its territory that it would have been allowed had it remained under the ABM Treaty’s maximum of 100.

The conundrum is whether the benefits of maintaining or adding to such defenses are greater than the costs of doing so, in terms of both expense and the increased likelihood that Russia and China would counter by greater numbers of and/or more capable missiles and countermeasures.

The Ground-Based Midcourse Defense System (GMD) centered on these interceptors in Alaska and California cannot singlehandedly defeat a concerted missile attack from Russia or China. The 2019 MDR acknowledges this fact, stating “the United States relies on deterrence to protect against large and technically sophisticated Russian and Chinese intercontinental ballistic missile threats to the U.S. homeland.”7 Yet the MDR also states “in the event of conflict, it [GMD] would defend, to the extent feasible, against a ballistic missile attack upon the U.S. homeland from any source.”8

Russia is already developing and deploying new long-range nuclear delivery systems to defeat current and expected future U.S. missile defense capabilities. A major question is whether Chinese leaders genuinely perceive such defenses to threaten the viability of their growing strategic deterrent force of around 180 missiles, after that force has been attacked by U.S. conventional or nuclear weapons. If the answer is “yes,” then the conundrum is whether the benefits of maintaining or adding to such defenses are greater than the costs of doing so, in terms of both expense and the increased likelihood that Russia and China would counter by greater numbers of and/or more capable missiles and countermeasures.

There are no clear or easy answers to these conundrums. Since its withdrawal from the ABM Treaty, the United States has acted as if the benefits of pursuing defenses outweigh the risks of arms racing with Russia and China and escalation of regional conflict. These posited benefits, which will vary based on the actual performance of defense systems, include strengthening deterrence, limiting the damage adversaries can inflict, and reassuring U.S. allies and partners in Europe, the Middle East, and East Asia.

Advocates of missile defense do not fully acknowledge that their programs drive Russia and China to develop and deploy offensive countermeasures. Instead, they cite the modernization of Russian and Chinese offensive nuclear forces as justifications for development of even more modern U.S. missile defenses and offensive weapons, continuing the action-reaction cycle. However, the unintended consequences—especially those that impact U.S. nuclear deterrence relationships with each major adversary—are equally important to consider.

Many of the Russian and Chinese nuclear capabilities that U.S. nuclear policymakers and politicians decry are, in part, responses to U.S. missile defense programs and their future potential capabilities. Russia’s much-vaunted new hypersonic weapons, including the intercontinental-range Avangard HGV and the regional-range Kinzhal ALBM, are notable not for their speed but their maneuverability, which may more easily circumvent U.S. defenses than traditional ballistic missiles. Similarly, the “exotic” Burevestnik nuclear-powered cruise missile and Poseidon nuclear-powered torpedo could evade interception and reinforce Russia’s second-strike capabilities. Russian Iskander deployments in and near Europe, now more than ten years old, were in response to U.S. and NATO Aegis Ashore plans.

For its part, China has developed ballistic missiles capable of delivering multiple warheads and penetration aids, including its newest DF-41 ICBM and the still in-development JL-3 SLBM, and an HGV-equipped medium-range missile, the DF-17. China’s growing numbers of warheads and dual-capable (nuclear and conventional) missiles and development of hypersonic boost glide systems reflect a determination to improve the survivability of the country’s relatively small nuclear arsenal against U.S. offensive strikes and defensive interceptions.

Perhaps paradoxically, as Russia and China develop maneuverable hypersonic weapons and other capabilities to bypass U.S. homeland missile defenses, they may solve (at least partially) the deterrence and instability challenges that U.S. ballistic missile defenses pose. North Korea and Iran are not (yet) capable of deploying such sophisticated offensive systems. Thus, U.S. homeland defenses predicated on ballistic missiles of the number that North Korea (and perhaps someday Iran) could deploy would not threaten forces as maneuverable as Russia’s or China’s. However, Moscow and Beijing would still worry and plan against future U.S. defense technologies, especially space-based ones.

Current U.S. missile defense policy will suffice if policymakers believe that unconstrained competition in offensive and defensive weapons is preferable to potential agreements that would provide transparency and potentially some limits on U.S. missile defense in exchange for possible Russian and Chinese concessions. However, U.S. interests and those of allies and the rest of the world would be better served by exploring what possible trade-offs could be negotiated between transparency and potential limitations on some U.S. missile defense capabilities, on one hand, and Russia and Chinese reductions and/or constraints on some of their current and prospective offensive capabilities, on the other.

The most promising way to assess these possibilities would be to explore whether and how regional and/or homeland missile defenses could be designed and deployed to protect against a lesser scale of missile threats (such as those posed by Iran and North Korea) without creating the realistic prospect that the United States could successfully negate a Russian or Chinese deterrent of U.S. first strikes against either Russia or China.


1 John Vandiver, “THAAD Anti-Missile System to Deploy to Romania,” Stars and Stripes, April 11, 2019,; Paul McLeary, “Japan Goes Big on Missile Defense, Aircraft: China Blames Trump for Tensions,” Breaking Defense, August 31, 2018,; and Paul McLeary, “Poland Signals Russia With Huge Missile Defense Deal,” Breaking Defense, March 28, 2018,

2 Kingston Reif, “The European Phased Adaptive Approach at a Glance,” Arms Control Association, updated January 2019,

3 On the planned U.S. sale of Aegis Ashore to Japan, see Mike Yeo, “Japan Suspends Aegis Ashore Deployment, Pointing to Cost and Technical Issues,” Defense News, June 15, 2020,

4 2019 MDR, 29–30.

5 Paul Sonne, “U.S. Military Tests Downing an ICBM From a Warship for First Time,” Washington Post, November 17, 2020, In response, Russian Foreign Affairs Ministry spokesperson Maria Zakharova said: “The recent test directly confirms the falsity of American assurances that the U.S. global missile defense system is not directed against Russia.” She continued, “This is direct evidence of a concrete example of how Washington manipulated the public opinion of its country, lied to its international partners and justified its actions in the international arena with absolutely far-fetched pretexts.” See: Tom O’Connor, “Russia Says U.S. Missile Defense Test Proves It Lied About Global Missile Shield,” Newsweek, November 19, 2020,

6 Tests of the Taepo Dong 2, Hwasong-14, and Hwasong-15 missiles have demonstrated potential intercontinental-range, but it is unclear if these missiles are now deployed or how many the DPRK might possess. It continues to conduct tests, including two tests of missile engines in December 2019, to improve its capabilities. See David Sanger and Choe Sang-Hun, “North Korea Links 2nd ‘Crucial’ Test to Nuclear Weapons Program,” New York Times, December 14, 2019,; and Joby Warrick, “North Korea Never Halted Efforts to Build Powerful New Weapons, Experts Say,” Washington Post, December 24, 2019,

7 This statement is significant in that it was a much more explicit acknowledgment that the United States and China are mutually vulnerable to the others’ strategic arsenals than the United States had expressed up to that point.

8 2019 MDR, xii.