Speed Kills Speed Kills Bruce M

Speed Kills Speed Kills Bruce M. Sugden Analyzing the Deployment of Conventional Ballistic Missiles

Should the United States deploy conventional ballistic missiles (CBMs) in support of the prompt global strike (PGS) mission?1 Most important, do the political-military beneªts outweigh the costs and risks of CBM deployment and use? The U.S. Department of Defense proposes to widen the range of conventional global strike options to shape the military investment decisions and defense policy choices of potential adversaries, to enhance U.S. nonnuclear deterrent options, and to hedge against future strategic uncertainty.2 Foremost among these options is the Conventional Trident Modiªcation (CTM) proposal, which entails deploying two Trident D-5 submarine-launched ballistic missiles (SLBMs), armed with conventional warheads, aboard every 24-tube Ohio-class ballistic missile submarine.3 The answers to the questions posed above have important implications for the allocation of ªnite U.S. defense resources, the structure of U.S. long-range strike forces, future arms control policy choices, and policies for strategic strike. Even a small-scale deployment of U.S. CBMs, for example, might have the potential to nullify a state’s or terrorists’ acquisition or use of weapons of mass destruction (WMD), especially when other U.S. weapons delivery options are not available for use.4 Furthermore, if the ability of U.S. long-range aircraft to penetrate enemy air defenses diminishes to a signiªcant degree,

Bruce M. Sugden is a defense analyst based in Washington, D.C. This article reºects the views of the author and does not represent the positions of his employer or clients.

For their comments and suggestions on earlier drafts of this article, the author thanks Emilie Cagigas, Jeffrey Engstrom, Charles Glaser, Jason Matheny, Jeffrey McKitrick, Timothy Miller, Megan Sullivan, Gregory Watson, and the anonymous reviewers.

1. The prompt global strike mission is deªned as the delivery of nonnuclear options against rap- idly emerging threats. See Kevin P. Chilton, “Statement on the United States Strategic Command,” testimony before the Strategic Forces Subcommittee, House Committee on Armed Services, 111th Cong., 1st sess., March 17, 2009, p. 8, http://armedservices.house.gov/pdfs/SF031709/Chilton_ Testimony031709.pdf. 2. U.S. Department of Defense, Quadrennial Defense Review Report (Washington, D.C.: Department of Defense, February 6, 2006), pp. 6, 31, 49. 3. There are fourteen Ohio-class ballistic missile submarines in the U.S. ºeet. 4. For the view that the likelihood of a weapon of mass destruction being used in a terrorist attack by the end of 2013 is higher than not, see Bob Graham, Jim Talent, Graham Allison, Robin Cleve- land, Steve Rademaker, Tim Roemer, Wendy Sherman, Henry Sokolski, and Rich Verma, World at Risk: The Report of the Commission on the Prevention of WMD Proliferation and Terrorism (New York: Vintage, 2008), p. xv, http://www.scribd.com/doc/8575216/WORLD-AT-RISK-Letters-of- Transmittal-Preface-Executive-Summary.

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large-scale deployment of CBMs might become critical to holding high-value targets at risk. In such an environment, CBMs would supplant long-range aircraft in high-risk military missions. Moreover, depending on the mode and extent of proposed U.S. CBM deployment, the United States could be constrained by international arms control treaties originally designed to limit nuclear weapons and their delivery vehicles. The call for a broader array of conventional strike options represents a school of thought that has existed for some time in the U.S. defense community. For example, the 2001 Quadrennial Defense Review, presaging the 2001 Nuclear Posture Review, called for nonnuclear forces that can strike with precision at ªxed and mobile targets and overcome anti-access and area-denial threats; and the 2004 U.S. Air Force Transformation Flight Plan stated that the Global Strike Concept of Operations is designed to enable joint forces to reach targets anywhere and at anytime.5 Finally, in 2006 former Secretaries of Defense Harold Brown and James Schlesinger argued that the increasing likelihood of terrorists obtaining nuclear weapons requires “prompt, precise, nonnuclear” options, such as the CTM.6 On the other hand, critics have argued that a nuclear-armed state may misinterpret CBM ºights, especially if the state detects the missiles traveling toward its territory, as those of nuclear-armed missiles.7 This misinterpretation might lead a state to launch its nuclear-armed ballistic missiles in response. The likelihood of an inadvertent nuclear response could be increased if it ap- peared the warheads would detonate over or on the state’s territory. Despite the persistent debate over the PGS mission and CBMs, there have been few comprehensive assessments of the political-military beneªts, costs, risks, and trade-offs of the PGS mission and deployment of long-range CBMs on land or aboard vessels at sea.8 The literature requires additional analysis of

5. Department of Defense, Quadrennial Defense Review Report (Washington, D.C.: Department of Defense, September 30, 2001), pp. 12, 14; and U.S. Air Force, The U.S. Air Force Transformation Flight Plan, 2004 (Washington, D.C.: Future Concepts and Transformation Division, Department of the Air Force, 2004), p. 45. 6. Harold Brown and James Schlesinger, “A Missile Strike Option We Need,” Washington Post, May 22, 2006. 7. See, for example, Joshua Pollack, “Evaluating Conventional Prompt Global Strike,” Bulletin of the Atomic Scientists, Vol. 65, No. 1 (January/February 2009), pp. 13–20. 8. Several studies have analyzed speciªc issues of the PGS mission and CBM deployment and use. First, Dennis M. Gormley has addressed the nexus of timely intelligence and conventional PGS missions. See Gormley, “Conventional Force Integration in Global Strike,” in James J. Wirtz and Jeffrey A. Larsen, eds., Nuclear Transformation: The New U.S. Nuclear Doctrine (New York: Palgrave Macmillan, 2005), pp. 53–68. Second, Barry D. Watts has argued that the principal requirement is persistent strike—to be in the vicinity of a target once it is detected in order to quickly defeat it— and that CBMs are a niche capability. See Watts, Long-Range Strike: Imperatives, Urgency, and Options

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alternate land- and sea-basing modes for PGS weapons systems, including outside of the continental United States, and a strategic assessment of the potential political-military implications surrounding deployment and use of PGS weapons systems, which is especially needed given the long lead times required for deploying cutting-edge technologies.9 I argue that the United States, if it works to mitigate the risk of misper- ception and an inadvertent nuclear response, should deploy near-term CBMs in support of the PGS mission. The prompt response of CBMs would likely be sufªcient to defeat many time-sensitive, soft targets, provided the requisite information—so-called actionable intelligence—was available on the targets, such as the projected period of time for a mobile target to remain stationary.10 Near-term CBMs, those capable of being deployed prior to 2013, would have the required attributes to defeat soft, ªxed targets: throw weight, payload ºexibility, and accuracy.11 Therefore, they would contribute to closing the prompt global strike gap, wherein high-value targets—such as terrorist leaders, WMD storage sites, and soft-site ballistic missile launchers being prepared

(Washington, D.C.: Center for Strategic and Budgetary Assessments, April 2005). Third, Bruce M. Deblois, Richard L. Garwin, R. Scott Kemp, and Jeremy C. Marwell have contended that space- based forms of power projection would be inferior to terrestrial forms based on capabilities and cost. See Deblois, Garwin, Kemp, and Marwell, “Space Weapons: Crossing the U.S. Rubicon,” In- ternational Security, Vol. 29, No. 2 (Fall 2004), pp. 50–84. Finally, Theodore A. Postol has analyzed the risk of ballistic missiles ºying over Russia and inadvertent nuclear retaliation. See Postol, “An Evaluation of the Capabilities and Limitations of Non-Nuclear-Armed Trident Ballistic Missiles for Short-Time Conventional Strikes,” paper presented before congressional staff at a meeting of the Center for Science, Technology, and Security Policy and the American Association for the Ad- vancement of Science, “Conventional Missiles and Early Warning Systems: The Proposed D-5 Tri- dent Conversion and the impact on Russia’s Early Warning System,” Rayburn House Ofªce Building, Washington, D.C., October 6, 2006, http://cstsp.aaas.org/ªles/GlobalStrikeSystem OverviewBrieªng_October5-6,2006_October3,2006-01.pdf. 9. For a comprehensive assessment, see National Research Council, Committee on Conventional Prompt Global Strike Capability, U.S. Conventional Prompt Global Strike: Issues for 2008 and Beyond (Washington, D.C.: National Academies Press, 2008). The major ºaw in the National Research Council’s assessment is the hasty dismissal of land-based CBMs outside the continental United States due to concerns over local politics and international treaties, though overseas bases would help to reduce some risks and improve prompt response (p. 5–5). As is discussed below, my analysis diverges from the National Research Council study in two ways. First, and most important, the relative promptness and ability to avoid overºight of nuclear powers in many potential scenarios suggest that forward-deployed CBMs are a better option than CBMs based in the continental United States. Moreover, large-scale deployment of forward-deployed, land-based CBMs would be more cost effective than large-scale deployment onboard submarines. Second, I am not as san- guine about the outcome of systematic CBM attacks on an adversary’s nuclear forces as the Na- tional Research Council is. 10. Soft targets are sites with minimal protection against the blast effects of conventional weapons. 11. The throw weight of a weapons delivery vehicle is the maximum weight of munitions the vehicle can carry for its combat radius; and payload ºexibility is the ability of a weapons delivery platform to carry an array of munitions.

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for attacks—emerge in regions where U.S. forward-deployed forces are unavailable for immediate employment against the targets, or there is insufªcient time to employ forces available in the region. More speciªcally, I conclude that the U.S. Navy’s CTM is a cost-effective, near-term, niche PGS option that would mitigate the concerns of CBM opponents. First, CTMs would more easily avoid ºying over nuclear-armed states while traveling to their targets than CBMs launched from the continental United States. This beneªt, coupled with other political-military measures, would help to ameliorate the risk of nuclear-armed states misinterpreting CBM ºights and inadvertently initiating a nuclear response. Midterm CBM deployment, such as options for deployment at forward operating bases, would also provide this beneªt. Second, considering its limited scale of deployment and the likelihood that actionable intelligence for PGS missions against ºeeting targets will continue to be rare in the near- and midterms, CTM is relatively cost effective. The analysis also explores the role of CBMs in expanded PGS missions: defeating sophisticated air-defense systems, mobile targets, and hard and deeply buried targets. Near-term CBMs will have a capability against soft, ªxed air- defense targets. Thus, they will enable entry of friendly aircraft into adversary airspace as part of major combat operations. This mission will rise in importance if potential adversaries of the United States deploy air-defense systems that undermine the advantages of stealthy U.S. aircraft. Large-scale use of CBMs, however, could increase the risk of inadvertent nuclear escalation when the missiles travel near or over nuclear-armed states. Moreover, the large-scale use of midterm (2013–20) and long-term (2020 and beyond) CBMs against mobile targets as well as hard and deeply buried targets will require technologies that have yet to mature. I employ open-source material in a cost-beneªt analysis of potential PGS weapons systems. Subsumed under this framework is an assessment of the capabilities of notional weapons systems and the potential tactical and strategic effects of various PGS missions. The examination emphasizes that policymakers should consider PGS alternatives against a myriad of strategic issues, such as the risk of misinterpreting ballistic missile launches and shaping potential adversaries’ military investments, not just ªrst-order tactical effects. The analysis is developed over several stages. First, the article analyzes the need for the PGS mission and CBMs. Second, it evaluates the availability of actionable intelligence as the linchpin of PGS missions. The third section assesses the beneªts, costs and risks, and trade-offs surrounding several notional PGS weapons systems: land- and sea-based CBMs, manned aircraft, and armed unmanned aerial vehicles (UAVs). It also examines alternative basing modes and

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the use of long-term CBMs in expanded PGS missions as part of major combat operations. The fourth section explores the most prominent argument against ªelding CBMs, namely the risk of nuclear ambiguity and inadvertent escalation. The concluding section derives policy recommendations from the analysis.

What Is the Need for PGS and CBMs?

Proponents of the PGS mission argue that there is an immediate, niche mission that can be fulªlled only by CBMs. They also argue that, over the long term, CBMs might become more useful in large-scale missions to penetrate sophisticated air defenses and provide a wider range of prompt, nonnuclear strike options to the United States. Furthermore, some advocates of CBM deployment assert that the weapons could be used in a large-scale counternuclear role and to shape adversary military investments. As background, the U.S. global strike regime is a comprehensive network of intelligence-gathering sensors; command, control, and communications assets; military bases; logistical support; weapons; weapons delivery vehicles; and decisionmakers. The regime’s purpose is to strike high-value targets and to gain and maintain U.S. access to enemy airspace. These strikes may be exe- cuted within short time lines and at extended distances from the continental United States and forward operating bases. Within this regime is a six-stage “kill chain”: ªnd, ªx, track, target, engage, and assess. As discussed below, the PGS mission and CBMs are directed at compressing the “engage” part of the cycle, but some PGS weapons system options, such as aircraft, can play roles in reducing time lines in other areas as well, such as the amount of time required for ªnding a target.12

the case for the near-term, niche mission The near-term PGS mission is intended to defeat emerging, time-sensitive, soft targets, such as exposed WMD launchers, terrorist leaders, and sites of state transfers of WMD to terrorists or other states within roughly one hour of a decision to attack.13 These targets may appear during any period in peacetime

12. See Adam J. Hebert, “Compressing the Kill Chain,” Air Force Magazine, Vol. 86, No. 3 (March 2003), pp. 50–54. 13. James E. Cartwright, “Statement on U.S. Nonproliferation Strategy and Roles and Missions of the Department of Defense and Department of Energy in Nonproliferation,” testimony before the Emerging Threats and Capabilities Subcommittee, Senate Armed Services Committee, 109th Cong., 2d sess., March 29, 2006; Peter C.W. Flory, “Statement Regarding Global Strike Issues,” testimony before the Strategic Forces Subcommittee, Senate Armed Services Committee, 109th Cong.,

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and wartime when U.S. forces are unavailable in the vicinity or are otherwise committed. Both the 1998 cruise missile strikes against al-Qaida’s Tarnak Farm and other camps in eastern Afghanistan, which failed to kill al-Qaida’s leader- ship, and the opening F-117 air attack in Operation Iraqi Freedom on March 19, 2003,14 which destroyed a bunker where Iraqi President Saddam Hussein was thought to be located, underscore the importance of coupling prompt weapons delivery vehicles to accurate, actionable intelligence to hold time-sensitive targets at risk.15 The National Research Council conducted a study on the mission requirements for using CTM and alternative systems as PGS weapons systems. Its ªnal report stated that there is a PGS capability gap, wherein U.S. nonnuclear strike capabilities fall short of those required for the current and projected security environments. The gap is illustrated by credible scenarios where two independent conditions for employing CBMs might exist: U.S. manned or unmanned aircraft are not deployed close enough to the targets to enable prompt attack; or enemy air defenses are strong enough to jeopardize the success of a mission carried out by aircraft.16 Even if U.S. long-range bombers were deployed to Guam or Diego Garcia, for example, it could take up to ten to twenty hours of ºight time to reach distant targets.17 Because CBMs could hit distant targets from bases in the continental United States within a one- hour time period, proponents argue they are the ideal PGS weapons system.

the case for the long-term, expanded mission The second type of PGS mission involves a strike at a larger set of distant, time-critical targets at the opening of major combat operations.18 Appropri-

2d sess., March 16, 2006; Brown and Schlesinger, “A Missile Strike Option We Need”; and National Research Council, U.S. Conventional Prompt Global Strike, p. 2-5. 14. Michael R. Gordon and Bernard E. Trainor, Cobra II: The Inside Story of the Invasion and Occupa- tion of Iraq (New York: Pantheon, 2006), pp. 169–177. The missile strikes were launched in response to the attack on the naval vessel USS Cole. 15. Most critics of CBM deployment do not disagree with the importance of PGS missions. The core disagreement is over the cost-beneªt ratio of CBMs relative to other options such as aircraft. See, for example, Pollack, “Evaluating Conventional Prompt Global Strike”; and Steve Andreasen, “A Misguided Missile Proposal,” Philadelphia Inquirer, March 14, 2006. 16. The ºight time alone for subsonic aircraft exceeds one hour for distances of roughly 500 nautical miles or more. National Research Council, U.S. Conventional Prompt Global Strike, p. 1-4. 17. For forward-deployed systems, hypersonic cruise missiles are an option. Traveling between Mach 4 and Mach 8, hypersonic cruise missiles could range from 1,000 to 2,000 nautical miles in thirty to sixty minutes. See ibid., pp. 4-8, 4-9, 4-22, 4-23. Hypersonic cruise missiles would be an improvement over subsonic cruise missiles for performing PGS missions. Because hypersonic cruise missiles would probably be launched from ships or aircraft, however, they would have some of those platforms’ strengths and limitations, such as potentially being in a suboptimal posi- tion relative to the target at the moment the opportunity to strike emerges. Thus, I do not analyze hypersonic cruise missiles in the section on PGS options. 18. National Research Council, U.S. Conventional Prompt Global Strike, pp. 2-5, 2-6.

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ate targets include command, control, and communications nodes and air defenses. The political-military circumstances, mission requirements, and weapons systems capabilities for ensuring successful strikes differ from the near-term, niche mission. According to proponents, expanded roles for CBMs could also include counternuclear missions and the shaping of adversary military investments. These roles are predicated on a large-scale CBM capability, perhaps a minimum of ªfty deployed CBMs. The argument for CBMs in the expanded mission is twofold. One rationale is that an adversary’s defense of a critical capability may pose serious risk to aircraft and aircrews attempting to bomb the target, but a weapon traveling at ballistic speed is guaranteed to penetrate most, if not all, defenses. Thus, CBMs would increase the probability of destroying heavily defended targets, such as those on the coast of the People’s Republic of China opposite Taiwan.19 CBMs could also play a role in opening the door to manned aircraft as part of a major combat operation. There would be a greater requirement for CBMs and large-scale PGS missions to defeat defensive systems and enable entry for U.S. strike aircraft under two conditions. First, the long-term international security environment will be marked by a greater diffusion of anti-access and area-denial weapons systems, mobile targets, and hard and deeply buried targets compared with today.20 Anti-access and area-denial systems increase the distance between targets and areas from which the United States can operate its military forces with impunity. Command and control centers for these systems might be mobile or deep and hardened against many direct attack options. The second condition is that area-denial weapons technology overturns the dominance of stealth technology. These conditions would put a premium on defense penetration; persistence and high volume of ªre; intelligence, surveillance, and reconnaissance and target acquisition; payload ºexibility; throw weight; and increased transparency regarding ballistic missile payloads. This option for CBMs will require developing and ªelding capabilities that are unavailable in the near term. Thus, this analysis considers the use of CBMs in expanded PGS missions to be a long-term option. The near-term PGS mission and CBM options, such as CTM, do not focus on major combat operations; they are stand-alone, limited, prompt strike options.

19. Ofªce of the Secretary of Defense, Annual Report to Congress: The Military Power of the People’s Republic of China, 2008 (Washington, D.C.: Department of Defense, 2008), p. 42. 20. Andrew Krepinevich, Barry Watts, and Robert Work, Meeting the Anti-Access and Area-Denial Challenge (Washington, D.C.: Center for Strategic and Budgetary Assessments, 2003). For information on hard and deeply buried targets, see U.S. Secretary of Defense and Secretary of Energy, “Re- port to Congress on the Defeat of Hard and Deeply Buried Targets” (Washington, D.C.: July 2001), http://www.nukewatch.org/facts/nwd/HiRes_Report_to_Congress_on_the_Defeat.pdf.

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The second rationale for CBMs in an expanded mission is that a wider array of conventional strike options will allow the United States to avoid crossing the nuclear threshold; they will provide usable tools for escalation that are pro- portionate to the threat that needs to be deterred or defeated. In contrast, the use of nuclear weapons against most anticipated non-WMD threats is deemed disproportionate. Using nuclear weapons, even against WMD targets, will en- gender a host of undesired political consequences.21 Therefore, the threat to launch a conventional strike would be more credible, which is conducive to managing the escalation of the use of force below the nuclear threshold and to ensuring the success of deterrence. This line of thinking echoes the Cold War doctrine of ºexible response, wherein the United States and its allies were prepared to ªght at all levels of war to deter the Soviet Union from all forms of military aggression.22 A U.S. Department of Defense ofªcial, for example, de- clared in a 2002 brieªng on the Nuclear Posture Review that “the non-nuclear strike forces, we believe, have the potential, if fully exploited, fully developed, to reduce our dependency on nuclear forces for the offensive-strike leg.”23 the counternuclear mission. Some CBM proponents argue that long- term CBMs might be used in a large-scale, counterforce role to defeat nuclear forces. For example, U.S. CBMs could nullify a nuclear strategy that China might employ to deter U.S. intervention in a Taiwan Strait conºict. Many of China’s nuclear-armed intercontinental ballistic missiles (ICBMs) are based at ªxed sites, and U.S. CBMs could be used to undertake a preventive or preemptive strike against their silos or soft-site launch pads, or to functionally defeat their exit from secure storage sites.24 Were the nuclear adversary operating under a launch-on-warning or launch-under-attack doctrine, however, or if mobile ICBMs were deployed from their garrisons, U.S. CBMs might fail to destroy all the nuclear missiles on the ground.25 A large-scale, counternuclear mission would emphasize intel-

21. George H. Quester, Nuclear First Strike: Consequences of a Broken Taboo (Baltimore, Md.: Johns Hopkins University Press, 2005). 22. For a discussion of how ºexible response was conceptualized and applied in the North Atlan- tic Treaty Organization, see Ivo H. Daalder, The Nature and Practice of Flexible Response: NATO Strat- egy and Theater Nuclear Forces since 1967 (New York: Columbia University Press, 1991). 23. J.D. Crouch, “Special Brieªng on the Nuclear Posture Review,” news transcript (Washington, D.C.: Department of Defense, January 9, 2002), http://www.defenselink.mil/transcripts/2002/ t01092002_t0109npr.html. 24. I thank Timothy Miller for bringing this mission to my attention. Although China deploys mobile DF-31A ICBMs, they are kept in garrison during peacetime, and their warheads are suppos- edly stored at separate locations. 25. Charles L. Glaser and Steve Fetter, “Counterforce Revisited: Assessing the Nuclear Posture Re- view’s New Missions,” International Security, Vol. 30, No. 2 (Fall 2005), pp. 104–107. For more on launch-on-warning doctrine, see Richard L. Garwin, “Launch under Attack to Redress Minuteman Vulnerability?” International Security, Vol. 4, No. 3 (Winter 1979/80), pp. 117–139.

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ligence, surveillance, and reconnaissance, as well as target acquisition and CBM accuracy and reliability, but these capabilities would not be as strong as required at any given moment. In this scenario, the potential effect could be the adversary launching surviving nuclear missiles against U.S. forward- deployed military assets, allies, or territory. Although preemptive counternuclear strikes might be warranted under a particular set of political-military circumstances, conventional counternuclear strikes could result in nuclear escalation. Although the National Research Council refused to endorse the large-scale counternuclear mission for conventional PGS weapons systems, it contends that the probability of a nuclear response to a conventional attack is lower than the probability of a nuclear response to a nuclear attack.26 The logic of the council, however, is not compelling under all conditions. The effect of highly accurate strikes on nuclear forces could be the same regardless of whether they were conducted with conventional or nuclear weapons: the targeted state’s deterrent capabilities might be decimated, and the state would be more vulnerable to U.S. coercion. To prevent this situation from coming to fruition, the state would have to consider launching its nuclear forces under warning or attack rather than risk the failure of riding out a strike. Moreover, unless the United States develops a retargeting capability for in- ºight ballistic missiles, major nuclear powers such as Russia and China will have survivable forces. Russia already has a substantial arsenal of mobile ICBMs, and China is deploying a mobile ICBM system.27 As demonstrated in the U.S.-led coalition search for mobile Iraqi missiles in the 1991 Persian Gulf War, mobility carries great beneªts in hiding from air- and space-based intelligence, surveillance, and reconnaissance assets.28 Therefore, countries with mobile nuclear weapons systems would have an incentive to ride out a U.S. CBM attack rather than launch under warning or attack. In the end, a counternuclear role for CBMs is best reserved for small-scale missions against nascent nuclear states—perhaps Iran and North Korea—that deploy ªxed-based, liquid-fueled nuclear-armed ballistic missiles that are vulnerable to surprise attacks. shaping of adversary military investments. Some proponents suggest that CBM deployment, especially if it were capable of large-scale attacks,

26. National Research Council, U.S. Conventional Prompt Global Strike, pp. 3-7, 3-20. 27. Ofªce of the Secretary of Defense, Military Power of the People’s Republic of China, 2008, p. 25; and Robert S. Norris and Hans M. Kristensen, “Chinese Nuclear Forces, 2008,” Bulletin of the Atomic Scientists, Vol. 64, No. 3 (July/August 2008), pp. 42–45. 28. Barry R. Posen, “Command of the Commons: The Military Foundation of U.S. Hegemony,” In- ternational Security, Vol. 28, No. 1 (Summer 2003), p. 30.

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might allow the United States to shape adversaries’ military investment strategies.29 Just as U.S. aircraft technology imposes costs on potential adversaries, whereby they invest additional resources into defensive systems to hinder U.S. air operations, adversaries might choose to invest additional resources into ballistic missile defense systems.30 Therefore, the adversary would be funnel- ing scarce defense funds into defensive weapons systems and corresponding operations rather than into offensive systems. Ballistic missile defense, however, is so ªnancially costly and difªcult to make effective that adversaries might be reluctant to vigorously pursue it.31 Instead, they might invest more resources in passive measures, such as reinforcing hardened and buried sites and deploying assets on mobile transports. Given that some potential adversaries are already pursuing this path, CBMs might strengthen a perceived investment need that is relatively benign to the United States.32 Overall, although it is uncertain whether U.S. CBM deployment could impose costs on potential adversaries, in the absence of U.S. improvements in long-range strike capability, the opportunity to impose costs will dissipate.33

The Challenge of Intelligence

Although lack of access to classiªed intelligence-collection methods precludes an exhaustive analysis of the near-term pervasiveness of actionable intelli-

29. On the difªculty of assessing the indirect effects of defense policies and military operations, see James G. Roche and Barry D. Watts, “Choosing Analytic Measures,” Journal of Strategic Studies, Vol. 14, No. 2 (June 1991), pp. 165–209. 30. In what is widely perceived as a reaction to U.S. offensive air capabilities, China is investing in advanced surface-to-air missile systems along its coast opposite Taiwan and in defense of strategic assets. See Ofªce of the Secretary of Defense, Annual Report to Congress: The Military Power of the People’s Republic of China, 2006 (Washington, D.C.: Department of Defense, 2006), pp. 21, 30. 31. For example, in 2006 the Congressional Budget Ofªce estimated that total investment costs for U.S. limited missile defense, if current plans are carried out, would peak at about $15 billion (ex- cluding cost risk) in 2016. This is projected to diminish as the procurement phase ends and missile defense systems become operational. Congressional Budget Ofªce, Long-Term Implications of Cur- rent Defense Plans: Summary Update for Fiscal Year 2007 (Washington, D.C.: Congressional Budget Ofªce, October, 2006), p. 22. On the projected effectiveness of national missile defense, see Charles L. Glaser and Steve Fetter, “National Missile Defense and the Future of U.S. Nuclear Weapons Pol- icy,” International Security, Vol. 26, No. 1 (Summer 2001), pp. 49–54. In comparison, according to the Stockholm International Peace Research Institute (SIPRI), Russia’s and China’s total 2005 defense expenditures are estimated at $21 billion and $41 billion, respectively. See Stockholm International Peace Research Institute, “The 15 Major Spender Countries in 2007” (Stockholm: SIPRI, 2008), http://www.sipri.org/contents/milap/milex/mex_major_spenders.pdf. It is worth noting that some countries might purchase missile defense capabilities, albeit limited, from foreign sources. See Doug Richardson, “Iran May Have Lined Up S-300 SAM Systems,” Jane’s Defense News, Janu- ary 9, 2008. 32. Andrew F. Krepinevich, Defense Investment Strategies in an Uncertain World (Washington, D.C.: Center for Strategic and Budgetary Assessments, 2008), pp. 52–53. 33. Watts, Long-Range Strike, pp. 38–39.

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gence that would enable use of CBMs against time-sensitive targets, available evidence suggests that a myriad of intelligence collection sensors and sources will periodically provide the timely and detailed information required for successful execution of a PGS mission.34 Accurate intelligence that is conducive to PGS strikes within a one-hour time period places a high demand on a persistent presence in geographic areas of interest to detect and track time-sensitive targets, especially mobile ones, but U.S. imagery intelligence capabilities alone do not meet the demand. First, fast-pass reconnaissance in the form of satellites is not conducive to persistent reconnaissance of small geographic areas containing ºeeting targets. Recon- naissance satellites optimize their resolution of imagery through low orbits, typically below an altitude of 1,000 miles, which give them a few minutes of coverage over a speciªc area per pass.35 These satellites were designed for wide-area coverage to scan ªxed targets in support of strategic warning. For example, reconnaissance satellites are excellent tools for taking snapshots over time to show changes in the size and location of large military formations, such as armored units, aircraft units, and ballistic missile emplacements. Notwithstanding the limitations of imagery satellites, U.S. space-based radar reconnaissance satellites, if fully deployed in the long term, will provide improved persistent coverage of target areas.36 The maximum time gaps between observations might be in the tens of minutes. The system’s projected 2020 capability will enable more reliable space-based target detection and identiªcation compared to the near-term capability. A second issue is that although it is difªcult for large military formations and ªxed sites to hide from a variety of reconnaissance assets, small, mobile targets such as trucks and individuals ªnd the task relatively easier. These types of targets can avoid open areas and employ cover and concealment to reduce the probability of detection. More capable means of persistent reconnaissance and intelligence collection are aircraft and human intelligence sources on the ground near the targets. These tools are the basis for Israel’s counterleadership strikes against Hamas,

34. The requisite intelligence, however, will not always be available when desired. For example, even with the focus of U.S. intelligence assets on Iraq during the launch of Operation Iraqi Free- dom in 2003, U.S. global strike forces failed to kill any of the top ªfty-ªve ofªcials in the government of Iraq. See Gordon and Trainor, Cobra II, p. 410. 35. For information on reconnaissance satellite operations, see Emily Clark, “Military Reconnais- sance Satellites (IMINT),” in Terrorism Project (Washington, D.C.: Center for Defense Information, October 16, 2001), http://www.cdi.org/terrorism/satellites.cfm; and Thomas Behling and Ken- neth McGruther, “A New Doctrine: Planning Satellite Reconnaissance to Support Military Opera- tions,” Studies in Intelligence (Winter 1998–99), https://www.cia.gov/library/center-for-the-study- of-intelligence/csi-publications/csi-studies/studies/winter98_99/art10.html. 36. National Research Council, U.S. Conventional Prompt Global Strike, p. 2-22.

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the Palestinian Islamic Jihad, and the al-Aqsa Martyrs’ Brigade.37 Moreover, reconnaissance via UAVs and intelligence from informants enabled U.S. strikes against six suspected al-Qaida terrorists in Yemen in November 2002 and al- Qaida in Iraq’s leader, Abu Musab al-Zarqawi, in Iraq in June 2006.38 Despite some successes, there are problems with relying on human intelligence sources and UAV reconnaissance. First, the history of receiving reliable intelligence from informants is mixed. For example, two U.S. attempts to kill Saddam Hussein with air strikes in 2003, based on information passed by Iraqi informants, failed.39 Informants can be dishonest and motivated more by ªnancial gain than by allegiance to the state seeking the information.40 Second, UAVs have to violate sovereign airspace to gather intelligence. If a UAV were detected or shot down, it might disrupt U.S. diplomatic efforts or relations with other states. The nearly global and persistent footprint of U.S. signals intelligence, which is information collected through the interception of broadcast communications and electronic transmissions, could compensate for shortfalls in other areas of intelligence collection. For example, the United States has successfully ident- iªed and tracked terrorist targets through signals intelligence and other collection tools.41 One target was tracked in Somalia and reported killed by Tomahawk cruise missiles from an offshore U.S. naval vessel. Therefore, the combination of intelligence disciplines could create an accurate and timely pic- ture of events that prompt weapons delivery vehicles could exploit.42

Weighing Prompt Global Strike Options

In this section I describe four notional PGS options and analyze them against the backdrop of nine capabilities for a PGS weapons system, plausible basing

37. Daniel Byman, “Do Targeted Killings Work?” Foreign Affairs, Vol. 85, No. 2 (March/April 2006), p. 100. 38. Globalsecurity.org, “MQ-1B Armed Predator UAV,” in Intelligence, GlobalSecurity.org, http:// www.globalsecurity.org/intell/systems/armed-predator.htm; and Cal Perry, Jamie McIntyre, Barbara Starr, Henry Schuster, and Randa Habib, “Cell Phone Tracking Helped Find al-Zarqawi,” CNN.com, June 10, 2006, http://www.cnn.com/2006/WORLD/meast/06/09/iraq.al.zarqawi/. 39. Gordon and Trainor, Cobra II, pp. 169, 177, 409. 40. See, for example, Jeffery T. Richelson, A Century of Spies: Intelligence in the Twentieth Century (New York: Oxford University Press, 1995). 41. See Eric Schmitt and Jeffrey Gettleman, “Qaeda Leader Reported Killed in Somalia,” New York Times, May 2, 2008; and Scott Shane, “Inside a 9/11 Mastermind’s Interrogation,” New York Times, June 22, 2008. 42. According to the U.S. Government Accountability Ofªce (GAO), the Department of Defense has not fully assessed the intelligence, surveillance, and reconnaissance capabilities that will enable complex, large-scale PGS and CBM operations. United States Government Accountability Ofªce, “Military Transformation: DOD Needs to Strengthen Implementation of Its Global Strike Concept and Provide a Comprehensive Investment Approach for Acquiring Needed Capabilities,” GAO-08-325 (Washington, D.C.: U.S. GAO, 2008), p. 29.

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schemes, and potential political-military costs, beneªts, and trade-offs. Al- though PGS proponents generally advocate for CBM options, a complete analysis must address whether other options can close the PGS gap. Moreover, the relative beneªts of basing schemes for PGS weapons systems need to be assessed against preferred capabilities, risks to be avoided, international treaty obstacles, ªnancial costs, and potential responses of adversaries.43 In general, basing schemes may be considered in the continental United States or outside at forward operating bases, and on land or sea (ship or submarine).44 According to the U.S. Department of Defense, PGS is subsumed under the broader global strike joint integrating concept, which describes how a joint military force integrates capabilities in the future to generate desired tactical, operational, and strategic military outcomes.45 The Department of Defense measures global strike capabilities using ªve attributes: responsiveness, surprise, survivability, persistence, and effects spectrum.46 The essential components of these attributes are analyzed in this section in relation to military utility: prompt response, defense penetration, prelaunch survivability, combat radius, persistence, weapons delivery accuracy, throw weight, payload ºexibility, and target acquisition. Table 1 provides examples of existing and notional weapons systems to illustrate the different capabilities and trade-offs across systems.

conventional ballistic missiles There are both proposed sea- and land-based options for CBMs. The near-term PGS solution for the Department of Defense is the U.S. Navy’s CTM.47 The

43. The Strategic Arms Reduction Treaty (START) potentially presents several signiªcant issues for land- and sea-based CBM deployment because it captures any land-based ballistic missile with a range greater than 5,500 kilometers, regardless of payload, as an ICBM; and any ballistic missile contained in or launched from a submarine with a range in excess of 600 kilometers as an SLBM. Russia and the United States are negotiating an extension to START. See Alexei Arbatov and Rose Gottemoeller, “New Presidents, New Agreements? Advancing U.S.-Russian Strategic Arms Con- trol,” Arms Control Today, Vol. 38 (July/August 2008), pp. 6–14. 44. For an analysis of missiles based on earth-orbiting platforms, see Congressional Budget Ofªce, Alternatives for Long-Range Ground-Attack Systems (Washington, D.C.: Congressional Budget Ofªce, March 2006); and Deblois et al., “Space Weapons,” pp. 50–84. The high relative cost of space-based PGS weapons systems excludes them from this analysis. 45. Department of Defense, Global Strike JIC, ver. 1.0, January 10, 2005, http://www.dtic.mil/ futurejointwarfare/jic.htm. 46. The term “effects spectrum” is U.S. Defense Department jargon for striking a target with the appropriate weapon to achieve the desired effect. See ibid. 47. Because CTM is the U.S. Department of Defense’s favored near-term option, it has analyzed the option’s compliance with treaty obligations. The Defense Department maintains that CTM is not a new type of SLBM and will have the same number of warheads attributed to it as to its nuclear variant (eight warheads). For small deployments, in fact, counting any CBM as a nuclear- armed missile resolves many arms control issues. See Brian R. Green, Deputy Assistant Secretary of Defense Strategic Capabilities, “Statement before the Strategic Forces Subcommittee, Senate Armed Services Committee, Regarding Global Strike Issues,” 110th Cong., 1st sess., March 28, 2007.

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Table 1. Existing and Notional Prompt Global Strike Weapons Delivery Options

Option Accuracy Combat Radius Speed Throw Weight Conventional 3–5 meters ϳ6,479 nautical Ͼ 15,000 miles 6,173 pounds Trident miles (nm) per hour (mph) (lbs) Modification at burnout (CTM) Conventional 3–5 meters ϳ6,000 nm Ͼ 15,000 mph ϳ2,000 lbs strike missile at burnout (CSM-1) MQ-9 3–5 meters; 1,655 nm 242 mph ϳ3,800 lbs Reaper laser- and armed Global unmanned Positioning aerial vehicle System (GPS)-guided munitions Tomahawk 10 meters Block 3: subsonic Block 3: (TLAM-C) 621 nm 694 lbs high sea-launched (submarine)/ explosive cruise 918 nm (surface missile combatant) AGM 86C/D Block 1-1A: Block 1: subsonic Block 1: air-launched 3–5 meters 513 nm 2,998 lbs/ cruise Block 2: missile 1,202 lbs (high-explosive penetrator) B-2A 3–5 meters; 3,300 nm high subsonic 40,000 lbs bomber GPS-guided munitions

SOURCES: Mark Daly, ed., Jane’s Unmanned Aerial Vehicles and Targets, No. 29 (Surrey, U.K.: Jane’s Information Group, 2007), pp. 268–271; Jamie Hunter, ed., Jane’s Aircraft Upgrades (February 6, 2009), Jane’s Information Group, http://www.janes.com; Duncan Lennox, ed., Jane’s Strategic Weapon Systems, No. 48 (Surrey, U.K.: Jane’s Information Group, 2008), pp. 182–183, 196, 209, 213; and National Research Council, Committee on Conventional Prompt Global Strike Capability, U.S. Conventional Prompt Global Strike: Issues for 2008 and Beyond (Washington, D.C.: National Academies Press, 2008), p. 6-6. In contrast to Jane’s, the National Research Council cites a range of 4,000 nautical miles and a throw weight of 1,000 pounds for the CTM. NOTE: Accuracy is measured in circular error probable, which is the radius of the circle centered on a target wherein 50 percent of the arriving weapons will impact. Combat radius refers to the maximum distance an aircraft can fly from its base with a full weapons load to a target and retain enough fuel to return to its base without aerial refueling. For a missile, it means the maximum range it can fly to a target from its launcher location. The throw weight of a weapons delivery vehicle is the maximum weight of munitions it can carry for its combat radius. Throw weights were converted from kilograms where applicable. The specifications for weapons in the research and development stage are subject to change.

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conventional model of the Trident D-5 SLBM would utilize conventional warheads and terminal guidance with assistance from the Global Positioning Sys- tem (GPS). Error-correcting reentry vehicles with GPS assistance have been proven in ºight in a Trident D-5 test program.48 According to the navy, the CTM’s reentry vehicle, which carries the warhead or munitions, would arrive at the target about one hour after a decision to attack was made. The CTM’s approximate range would be 6,479 nautical miles.49 The second option is the land-based CBM. Land-based CBMs are not pro- grammed in the defense budget, but potential midterm candidates might employ Minuteman III or Peacekeeper ICBM boosters that would deliver payloads beyond 6,000 nautical miles. A land-based CBM could carry an inert concrete slug (typically used in ICBM ºight tests), conventional explosives, or eventually a hypersonic glide vehicle that would carry weapons payloads weighing approximately 2,000 pounds and travel, when launched by an ICBM, roughly 9,000–10,000 nautical miles downrange and 3,000 nautical miles cross- range.50 Payloads might include penetrator warheads; wide-area munitions; small-diameter bombs; and UAVs for intelligence, surveillance, and reconnaissance missions. prompt response. Shortening the kill chain is the primary rationale for the PGS mission. The weapons system, however, comes into play only after a target has been found and a decision has been made to engage it. Thus, prompt response is deªned here as the time elapsed between a weapons system receiving an execution order and delivering a weapon on the target. For the same distance, ballistic missiles can arrive at the target in a shorter time span than aircraft, and forward-based ballistic missiles have a ªfteen-minute advantage over ballistic missiles launched from the continental United States.51 At least for near-term CBMs to defeat their targets, the targets must remain ªxed— unless there is in-ºight retargeting.52

48. Rear Adm. Charles B. Young, U.S. Navy, Director, Strategic Systems Program, “Statement before the Subcommittee on Strategic Forces, Senate Armed Services Committee, Fiscal Year 2007 Global Strike,” 109th Cong., 2d sess., March 29, 2006, p. 3. 49. Duncan Lennox, ed., Jane’s Strategic Weapon Systems, No. 46 (Surrey, U.K.: Jane’s Information Group, 2007), p. 206. 50. Congressional Budget Ofªce, Alternatives for Long-Range Ground-Attack Systems, p. xi; and Mi- chael Sirak, “Air Force Envisions Mid-Term, Prompt Global Strike Missile,” Defense Daily, July 7, 2006. 51. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-9. 52. It is plausible, however, for CBMs to employ a maneuvering reentry vehicle that uses organic active radar guidance, in combination with off-board sensors that would locate the target prior to missile launch, to home in on mobile targets. See ibid., p. 4-10. The U.S. Department of Defense concludes that China is conducting research and development on this CBM technology. See Ofªce of the Secretary of Defense, Annual Report to Congress: The Military Power of the People’s Republic of

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defense penetration. Defense penetration is the ability of a weapons system to survive against an adversary’s defensive capabilities until weapons impact. A ballistic missile, due to its speed, is far superior to aircraft in this capability. Ballistic missile reentry vehicles rely on high speed when entering the atmosphere to enable defense penetration.53 Furthermore, ballistic missiles can deploy penetration aids to confuse enemy missile-defense radars. In the long term, defense penetration might become more important as states invest in more sophisticated air-defense capabilities to deny adversaries access to their airspace.54 Moreover, as air-defense umbrellas continue to ex- pand in both quantity and quality, U.S. global strike systems will have to survive for longer periods of time in hostile, defended airspace before reaching targets in a country’s interior. This future environment could pose problems for some long-term CBM payloads such as glide vehicles. The National Re- search Council assesses that glide vehicles traveling in the atmosphere at speeds equal to or less than Mach 5 will be vulnerable to strong air defenses.55 prelaunch survivability. A weapons system’s ability to survive an attack prior to commencing its mission is its prelaunch survivability. This capability is important when bases for PGS assets are within range of adversaries’ strike systems. For example, U.S. bases in Japan and Guam, potential launch sites for PGS missions in the event of war between the United States and China, fall within range of Chinese ballistic missiles.56 Even when missiles are initially deployed outside potential adversaries’ threat rings, the United States should as- sume that adversaries will adapt and target these missiles once they are emplaced on ªxed launchers at forward operating bases. Thus, the prelaunch survivability of these ªxed assets will likely decline over time if adversaries develop long-range strike or sabotage capabilities.57 Because bases in the continental United States take U.S. weapons systems out of the range of most po-

China, 2009 (Washington, D.C.: Department of Defense, 2009), p. 21. Moreover, U.S. cruise missile technology has advanced to the point that enables in-ºight retargeting and dwelling capabilities. The ªrst cruise missile with these capabilities is the navy’s Tactical Tomahawk, which entered service in 2007. Jim Garamone, “Navy Accepts Tactical Tomahawk to Fleet,” American Forces Press Service, September 29, 2004, http://www.defenselink.mil/news/Sep2004/n09292004_2004092907 .html. 53. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-24. 54. Krepinevich, Watts, and Work, Meeting the Anti-Access and Area-Denial Challenge, pp. 3–7; and John A. Tirpak, “The Double-Digit SAMs,” Air Force Magazine, Vol. 84, No. 6 (June 2001), pp. 48–49. 55. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-21. 56. Ofªce of the Secretary of Defense, Military Power of the People’s Republic of China, 2008, p. 26. China’s DF-21A missile has a range of 1,350 nautical miles. Duncan Lennox, ed., Jane’s Strategic Weapon Systems, No. 48 (Surrey, U.K.: Jane’s Information Group, 2008), p. 26. 57. Depending on the threat environment over the long term, U.S. forward-deployed forces might require a robust ballistic and cruise missile defense umbrella to operate within an adversary’s threat ring.

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tential adversaries’ strike capabilities, they provide the highest level of prelaunch survivability but sacriªce prompt response. The geography and geology of some forward operating bases might preclude certain missile-basing schemes, which will determine to a large extent the prelaunch survivability of the missiles.58 The prelaunch survivability of missiles in hardened, underground silos, for example, is greater than ªxed, soft-site missiles, but less than mobile, dispersed missiles. Furthermore, hard, rocky soil can inhibit the cost-effective construction of hardened, underground silos, and the size of a base’s territory might not be conducive to mobile, dispersed missile operations. Base size might also preclude the use of soft-site launch pads because of threats emanating from outside the base’s security per- imeter. Some forward operating bases for CBMs such as Guam, however, might allow austere operations involving soft-site launchers. The less vulnerable weapons systems are to attack, the less tempting targets they will be to an adversary. Sea-based missiles, especially aboard submarines, are more survivable relative to ªxed missiles on land.59 The problem with sea- based missiles is that the vessel carrying the missiles adds to the cost of the weapons system. Initial deployment of a missile-carrying sea vessel, for example, is much more expensive than a soft-site missile launch pad or missile transporter-erector-launcher vehicle.60 The U.S. Navy’s plan to deploy two conventionally armed Trident D-5 missiles aboard each Ohio-class submarine, however, mitigates the cost. By replac- ing only two nuclear-armed Trident D-5s with the CTM, the navy reduces both

58. START limits ICBMs to three launch modes: silo and road- and rail-mobile transporter-erector- launchers. Fixed, soft-site (above-ground) launch pads are limited under START to test ranges and space launch facilities. Consequently, unless START expires or is renegotiated, it will pose problems for some proposed CBM basing schemes. 59. START prohibits “ballistic missiles with a range in excess of 600 kilometers, or launchers of such missiles, for installation on waterborne vehicles, including free-ºoating launchers, other than submarines.” U.S. Department of State, “Treaty between the United States of America and the Union of Soviet Socialist Republics on the Reduction and Limitation of Strategic Offensive Arms,” art. 5, par. 18a, http://www.state.gov/www/global/arms/starthtm/start/start1.html# ARTICLE5. 60. The Congressional Budget Ofªce estimates that a successor (SSBN(X)) to the Ohio-class ballistic missile submarine ºeet would cost around $6 billion per hull (in 2007 dollars) by the 2020s. Congressional Budget Ofªce, Options for the Navy’s Future Fleet (Washington, D.C.: Congressional Budget Ofªce, 2006), p. 22. The Congressional Budget Ofªce estimates (in 2006 dollars) the total acquisition cost of twenty-four long-range, land-based Peacekeeper CBMs, each carrying two hypersonic glide vehicles, at $4 billion. They would be based at soft-site launch pads in California and Florida. The average unit procurement cost would be $36 million. Finally, the total acquisition cost of forty-eight medium-range (3,200 nautical miles), land-based missiles, each carrying one hypersonic glide vehicle, based on twenty-four mobile launchers is estimated at $3.7 billion. The average unit procurement cost would be $26 million. For cost-analysis assumptions and method- ology on land-based systems, see Congressional Budget Ofªce, Alternatives for Long-Range Ground- Attack Systems, pp. xv, 48–55.

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the ªnancial cost of placing conventional missiles aboard submarines and the opportunity cost of supplanting survivable nuclear missiles with conventional missiles. combat radius. For a missile, combat radius is the maximum range it can ºy to a target from its launcher location. Typically, long-range missiles meant for intercontinental missions, such as the Trident D-5 SLBM and the Minute- man III ICBM, can travel farther than unrefueled long-range aircraft. For example, the CTM would have a combat radius of approximately 6,479 nautical miles, whereas a B-2A bomber has an unrefueled combat radius of 3,300 nautical miles. The U.S. Air Force’s midterm CBM option, the Conventional Strike Missile (CSM-1), might have a range of 6,000 nautical miles. U.S. CBM options must have a range exceeding the Intermediate-Range Nuclear Forces Treaty restriction. The treaty prohibits deployment of ballistic missiles with a range of less than 5,500 kilometers (2,969 nautical miles). The treaty will remain in effect with no expiration, unless the parties withdraw from it. Given their combat radii, land- and sea-based CBMs would hold much of the earth’s surface at risk. The CTM on submarines patrolling the eastern Atlantic, Indian, and western Paciªc Oceans would be able to cover targets in all global trouble spots that the Department of Defense anticipates. Land- based CBMs would also hold many areas at risk from various launch points, especially from forward-based sites. For example, assuming the CSM-1’s range of 6,000 nautical miles, it could strike Northwest Africa, Northeast Asia, and eastern China from Vandenberg Air Force Base in California. The same missile from Guam could reach targets throughout Asia and the Middle East, but not in Africa. And from the Falkland Islands (United Kingdom territory), the CSM-1 could strike targets within the continent of Africa, with the exception of those targets located in the far northeast area of the continent. International treaty obligations, however, might impede the United States from deploying land-based missiles to some of these bases if they are not on U.S. territory. Foreign governments, such as the United Kingdom if U.S. missiles were based at Diego Garcia or the Falkland Islands, could also block PGS operations originating from their soil. persistence. Persistence is the measure of time a weapons delivery vehicle can dwell over or outside of hostile territory in order to respond to emerging threats. An example is the B-1B bomber that was dwelling over Iraq in April 2003 and received an order to attack Saddam Hussein’s location. It dropped four 2,000-pound bombs, within one hour of target identiªcation, on a target in the al-Mansur district of Baghdad where Hussein was thought to be holding a

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meeting.61 This was essentially a PGS mission that exploited forward- deployed aircraft and benign airspace. Ballistic missiles are not persistent weapons systems in the same sense as aircraft, but alert CBMs could put bombs on target just as quickly as dwelling aircraft—if not more so—if the latter are not close enough to the targets. More- over, forward-deployed CBMs, on land or sea, could meet more requirements for persistent presence under some circumstances than CBMs based in the continental United States.62 weapons delivery accuracy. Accuracy of delivered weapons is deªned as the weapon’s circular error probable (CEP), which is the radius of the circle centered on a target wherein 50 percent of the arriving weapons will impact. Accuracy is vital to PGS missions for two reasons. First, given that near-term PGS missions are meant to defeat emerging, time-sensitive targets, inaccurate weapons delivery would likely translate into having to search for the ºeeting target again, a task that might be more difªcult as a result of the adversary learning from its mistake in poorly concealing the target from the ªrst attack. Second, weapons delivery accuracy is directly related to minimizing collateral damage and the concomitant political consequences.63 The less accurate the weapon, the more likely it will hit nonmilitary sites and cause noncombatant casualties. Ordinarily, payloads delivered by ballistic missiles, which are guided by an inertial or stellar navigation system, have a comparatively higher CEP than payloads delivered by aircraft.64 The Trident D-5 SLBM, for example, is reported to have a CEP of 90 meters.65 To obtain the CEP of aircraft- delivered payloads, ballistic missile reentry vehicles require GPS assistance

61. Gordon and Trainor, Cobra II, p. 409. 62. If deployed CBMs are captured by START as ICBMs, then to preclude rapid reloading of mobile ICBMs—deªned as reloading in four hours or less—there will be restrictions on the number of deployed and nondeployed spare missiles and missile transport equipment that may be located at all types of mobile ICBM bases. In addition, silo launchers may not be reloaded in less than twelve hours. 63. Collateral damage is deªned as the unintended destruction, including noncombatant casualties, resulting from military action. For a discussion of the political consequences of collateral damage, see Eric Victor Larson, Ends and Means in the Democratic Conversation: Understanding the Role of Casualties in Support for U.S. Military Operations, RAND Graduate School, 1996. 64. An inertial reference unit assists with navigation via measurements given by accelerometers and gyroscopes. See Oliver J. Woodman, “An Introduction to Inertial Navigation,” Technical Report, No. 696 (Cambridge: Computer Laboratory, University of Cambridge, August 2007), p. 5. With stellar guidance, or celestial reference, a missile follows a predetermined course that is continu- ously adjusted by referring to ªxed stars prior to the reentry vehicles entering the atmosphere. See Federation of American Scientists, “Ballistic Missile Basics,” in Special Weapons Primer, updated June 4, 2000, http://www.fas.org/nuke/intro/missile/basics.htm. 65. Lennox, Jane’s Strategic Weapon Systems, No. 46, p. 206.

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and steering capability for three-axis ºight control (roll, yaw, and pitch).66 Be- cause the U.S. defense industry is developing these capabilities for CBMs, and the Department of Defense will not likely deploy CBMs unless they are highly accurate, this analysis assumes that CBMs will have a CEP comparable to aircraft precision-guided munitions. Reentry vehicles delivered by CBMs, however, would be vulnerable to losing GPS signals due to vehicle maneuvers, enemy jamming, and plasma formation around the vehicle during the reentry phase.67 If the reentry vehicle does not reacquire GPS signals and make neces- sary corrections to its course, its payload could detonate beyond its aim point, potentially causing collateral damage. throw weight. A weapons delivery vehicle with a relatively heavy throw weight has two advantages. First, the heavier the throw weight of a weapons delivery vehicle, the more munitions it can carry to more targets. This means that one sortie might defeat several dispersed targets. In addition, instead of carrying more munitions, the delivery vehicle can carry fewer but heavier munitions, which might be better suited for speciªc missions. The throw weight of near-term CBMs would be sufªcient for defeating soft targets in small-scale PGS operations, such as surface facilities and shallow bunkers, but heavier throw weights become more important as the scope of PGS missions expands and hard and deeply buried targets enter the target set. In contrast to aircraft, the more limited throw weight of near-term CBMs, such as 8,708 pounds for the retired Peacekeeper ICBM, means that near-term CBMs will not pose a formidable risk to hard and deeply buried targets under- neath rock geology with a concrete structural thickness of 70–300 feet.68 The Department of Defense’s Defense Science Board suggests that optimum munitions would weigh 44,092–66,138 pounds, far exceeding existing missile throw weights.69 Accordingly, the U.S. Air Force has sponsored development of a 30,000-pound, aircraft-delivered, penetrating munition.70 The kinetic energy provided by ballistic missile munitions’ reentry speed may lessen the weight requirement for sufªcient earth-penetration capability against some buried targets, but destroying hard and deeply buried targets

66. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-26. 67. Ibid., p. 4-27. For information on the plasma sheath, see p. 4-31. 68. The Peacekeeper boosters might be used in land-based CBM options. Throw weight from “Memorandum of Understanding on the Establishment of the Data Base Relating to the Treaty between the United States of America and the Union of Soviet Socialist Republics on the Reduction and Limitation of Strategic Offensive Arms,” September 1, 1990, http://dosfan.lib.uic.edu/acda/ starthtm/memoundr.htm#meoundr. 69. U.S. Department of Defense, Report of the Defense Science Board Task Force on Future Strategic Strike Forces (Washington, D.C.: Department of Defense, February 2004), pp. 6–7. 70. Michael Sirak, “Massive Bomb to MOP Up Deeply Buried Targets,” Jane’s Defence Weekly, July 19, 2004, http://www.janes.com/defence/news/jdw/jdw040719_1_n.shtml.

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might remain problematic for CBMs. First, the kinetic energy, or velocity, of the warhead casing at impact is limited by the need for the warhead to survive penetration so that it can be detonated at the proper depth. The BLU-113, which has a penetration capability through concrete and earth greater than 20 feet and 100 feet, respectively, hits the ground at approximately 450 meters per second. Above 900 meters per second, the weapon would deform on impact and prior to detonation at the target.71 Ballistic missile reentry vehicles, however, typically deliver warheads at a speed in excess of 3,000 meters per second.72 Thus, CBMs require either a reentry vehicle capable of speed reduction maneuvers or boosters with heavier throw weight to threaten hard and deeply buried targets. Second, even earth-penetrating nuclear warheads with yields less than 1 kiloton or 1 megaton cannot destroy targets buried deeper than 50 or 300 meters, respectively, with hardness of 1 kilobar in granite.73 Finally, there are no technical hurdles for potential adversaries to overcome in digging deep enough to avoid the effects of earth penetrators. Commercial boring equipment, for example, can dig an 18-meter diameter tunnel at a rate of 70 meters per day.74 In the competition between offense and defense, the defender holds the cost advantage. The solution to CBMs defeating hard and deeply buried targets might be tactical rather than technological: functional defeat of hard and deeply buried targets, rather than their outright elimination, through repeated attacks on entryways, air ducts, and communications lines into the target.75 The implica- tion for CBMs is that without a technological breakthrough that makes heavy- lift capacity less costly relative to aircraft, even long-term CBMs will not be capable of destroying such targets. That mission will then be left to aircraft. payload ºexibility. The ability of a weapons delivery platform to carry an array of munitions translates into the ability to effectively attack a myriad of targets. The characteristics of a target, such as hardness, depth below or height above the surface, size of its surface area, and potential for collateral damage, drive the choice of munitions.

71. Michael A. Levi, “Fire in the Hole: Nuclear and Non-nuclear Options for Counterprolifera- tion,” Carnegie Report, No. 31 (Washington, D.C.: Carnegie Endowment for International Peace, November 2002), p. 17; Robert W. Nelson, “Low-Yield Earth-Penetrating Nuclear Weapons,” FAS - Public Interest Report, Vol. 54, No. 1 (January/February 2001), pp. 1–5; and Ivan Oelrich, Blake Purnell, and Scott Drewes, “Earth Penetrating Nuclear Warheads against Deep Targets: Concepts, Countermeasures, and Consequences” (Washington, D.C.: Federation of American Scientists, 2005), pp. 1–28. 72. Deblois et al., “Space Weapons,” p. 71. 73. Glaser and Fetter, “Counterforce Revisited,” p. 92. 74. Dennis M. Gormley, “Securing Nuclear Obsolescence,” Survival, Vol. 48, No. 3 (Autumn 2006), p. 134. 75. Levi, “Fire in the Hole,” pp. 20–21.

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Notwithstanding the lighter throw weight and poorer payload ºexibility of near-term CBMs compared to aircraft, CBMs could carry a sufªcient range of payloads to hold various soft-surface targets at risk. The CTM, for example, would carry kinetic energy projectiles consisting of tungsten rods for destroying soft targets in a wide surface area.76 In the midterm, the U.S. Air Force CSM-1 option might be capable of carrying kinetic energy projectiles and penetrator warheads weighing no more than 2,000 pounds.77 In the long term, CBMs might carry UAVs with weights under 3,000 pounds. The UAV payloads would provide persistent presence, high weapons-delivery accuracy, and target acquisition capability.78 In general, long-term CBMs would have greater payload ºexibility under either of two conditions. First, the weapons were packaged into smaller and lighter reentry vehicles through advanced minia- turization of explosives technology. Second, missiles were built with heavier throw weights so they could lift a wider variety of weapons. target acquisition. At least in the near term, ballistic missiles must rely on off-board sensors to locate targets prior to missile launch. Ballistic missiles will be conªned to striking ªxed targets because their retargeting capability will be largely nonexistent.79 If midterm or long-term payloads consisted of armed UAVs, however, they would allow remote human operators to visually acquire mobile targets. Research and development efforts must ªrst either overcome the challenges associated with high-speed dispensing of weapons during the reentry phase, such as ensuring the weapons avoid contact with other material and are protected against overheating, or develop speed- reduction maneuver technology.80 Boost-glide vehicles and GPS-assisted maneuvering reentry vehicles would also be able to react to updated target coordinates after launch.81 The sources of updated coordinates could be aircraft, satellites, or personnel on the ground.

manned and unmanned aircraft Air-breathing PGS options, those weapons delivery systems that travel through the atmosphere, are split between manned and unmanned aircraft. A long-range, manned, stealthy, subsonic bomber similar to the B-2A bomber, which can ºy intercontinental ranges without refueling, would rely more on design features and tactics conducive to stealth, rather than on speed, to sur-

76. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-14. 77. Ibid., p. 4-12. 78. Ibid., p. 4-16. 79. See information in n. 52. 80. National Research Council, U.S. Conventional Prompt Global Strike, p. 4-28. 81. Ibid., p. 4-30.

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vive in hostile airspace.82 An armed UAV would be the unmanned version of a PGS bomber. An example of UAV technology is the MQ-9 Reaper, a follow-on UAV to the MQ-1 Predator that has carried out several PGS missions, including the 2002 strike against al-Qaida terrorists in Yemen. The MQ-9 carries a combination of AGM-114 Hellªre missiles and Guided Bomb Unit (GBU)-12 and GBU-38 Joint Direct Attack Munitions (JDAMs).83 prompt response. An aircraft could deliver a weapon on a target faster than a ballistic missile if the aircraft were airborne near the target upon receipt of the order to attack. Aside from assuming the chance of ºying near an emerging target, this scenario presupposes reconnaissance of the target area as well as the ability of the aircraft and its crew to conduct sustained dwelling near the target area. Absent this scenario, aircraft cannot match the promptness of ballistic missiles. Moreover, aircraft operations are usually hindered by the need for overºight permission from third-party states and aerial refueling support. defense penetration. Against an adversary using the most advanced air- defense technology, aircraft designed for low-observable, stealthy ºight are more likely to penetrate defenses than aircraft that rely more on supersonic speed. A defender’s radar detects and tracks aircraft through reception of radar waves that have been reºected back from the aircraft, and the amount of power behind the reºected radar waves partly depends on the radar cross section of the aircraft.84 The lower the radar cross section, the more the aircraft de- creases the detection and tracking area of the defender’s radar. Thus, stealth features do not render aircraft undetectable; they reduce the span of time the defender has for detecting, tracking, and shooting down aircraft. In minimizing an aircraft’s radar cross section, engineers tend to sacriªce aerodynamic performance.85 This is why the next-generation U.S. bomber will probably not be capable of supersonic speed. Installing engines to make the aircraft capable of such speed would increase the infrared signature of an air-

82. Douglas Barrie and Amy Butler, “Next-Generation Bomber Sets Stage for ISR Penetrator,” Avi- ation Week & Space Technology, April 27, 2008. 83. John A. Tirpak, “UAVs with Bite,” Air Force Magazine, Vol. 90, No. 1 (January 2007); “MQ-9 Reaper Unmanned Aircraft System,” Air Force Link, http://www.af.mil/factsheets/ factsheet.asp?fsIDϩ6405; and Marina Malenic, “MQ-9 Reaper Flies First Iraq Mission,” Defense Daily, July 22, 2008. 84. Radar cross section is the area of the scattered radar wave being returned to the radar. It is the sum of the aircraft’s reºective components, such as the vertical stabilizer, fuselage, nose, and en- gine inlets. Radar cross section also varies with the wave frequency of the particular radar being used. Improving the low-observable features of the aircraft includes reductions in infrared, visual, and acoustic signatures. Rebecca Grant, The Radar Game: Understanding Stealth and Aircraft Surviv- ability (Arlington, Va.: IRIS Independent Research, 1998), pp. 23, 26, 37. 85. Ibid., p. 26.

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craft whose mass already makes the task of reducing its radar cross section difªcult. Because a UAV lacks life-support equipment and space requirements for an aircrew, it would have less mass and a comparatively smaller radar cross section than a manned bomber with the same combat radius and payload capacity. Therefore, all else being equal, the UAV would probably be stealthier and more survivable in hostile airspace. prelaunch survivability. Although aircraft share the same risk of coming under attack as soft-site and silo-based missiles while stationed at forward operating bases, they are not permanently ªxed at those locations. Compared to missiles, aircraft may easily relocate to alternate forward operating bases and remain in striking distance of adversaries. Aircraft in hardened shelters or placed on alert (with aircrews) near runways to react quickly to tactical warning of attack, meaning the attack is under way but weapons have yet to impact the target areas, are less vulnerable to attack than unsheltered or non-alert aircraft. Aircraft shelters, built with reinforced concrete or steel, enable aircraft to survive blast effects from nearby high-explosive detonations but usually not a direct hit if the weapon were carried in a casing designed for penetration.86 The concern for aircraft prelaunch survivability, however, is related more to the long-term PGS mission against major adversaries, which can strike U.S. airªelds, than to near- and midterm missions against terrorists and states that lack long-range strike capabilities. combat radius. For aircraft, combat radius refers to the maximum distance an aircraft can ºy from its base with a full weapons load to a target and return to its base without aerial refueling. Once aerial refueling is considered, however, the distance long-range aircraft are able to travel is limited only by the stamina of the aircrew in a highly conªned space. For example, the unrefueled combat radius of the B-2A bomber is reported to be 3,300 nautical miles; and it increases to more than 5,000 nautical miles with one aerial refueling.87 As discussed above, however, the trade-off for aircraft between greater combat radius and prompt response is more signiªcant than for ballistic missiles. For UAVs, of course, stamina of aircrews is not a consideration, and aerial refueling of UAVs would stretch their endurance beyond several days. With- out aerial refueling, the combat radius of the MQ-9 Reaper UAV is 1,655 nauti-

86. Roger Cliff, “‘China’s Military Modernization and the Cross-Strait Balance’: Testimony before the U.S.-China Economic and Security Review Commission, September 15, 2005” (Santa Monica, Calif.: RAND, 2005), pp. 4–5. 87. This combat radius assumes a combat loadout of eight AGM-129s and eight B61 bombs total- ing 24,000 pounds, and a “hi-hi-hi” ºight proªle. See Jamie Hunter, ed., Jane’s Aircraft Upgrades (Surrey, U.K.: Jane’s Information Group, February 6, 2009), http://www.janes.com.

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cal miles.88 With aerial refueling, the primary limiting factor for UAV missions might be oil and lubricants for the aircraft’s mechanical parts.89 Compared to the endurance limitations for manned aircraft, those for UAV operations would facilitate persistence in hostile airspace. Forward operating bases also facilitate persistence and the aircraft option by reducing the distance and ºight time to targets, thereby increasing sortie rates. The shorter the distance and time to the target, the more time the aircraft can commit to persistent operations over or near hostile territory. persistence. Persistence is related to survivability and effective combat radius of the weapons platform. The less stealthy an aircraft, the less survivable it is; therefore, it would not be a relatively optimal candidate for persistence in hostile, defended airspace. In addition, the shorter the distance from its base to its patrol area and the greater its combat radius, the longer the aircraft can dwell. Aerial refueling will increase the aircraft’s dwell time, but it should oc- cur outside the defender’s threat ring to safeguard the vulnerable tanker aircraft. Moreover, as discussed above, manned aircraft are constrained by the limits of human endurance.90 Although the percentage of weight and volume saved by eliminating the aircrew diminishes as a UAV’s combat radius and payload are increased, the organic combat radius and payload do not need to be increased to enhance the UAV’s military capability. Combat radius can be increased with aerial refueling, and lack of an aircrew means the UAV can remain aloft for a longer period of time. Together, these factors inherent to a UAV improve its ability to persist in hostile airspace relative to a manned aircraft. Thus, the persistence of an aircraft such as the B-2A bomber could be increased by eliminating the aircrew. The operational beneªt of persistence is that it enables aircraft to dwell in an area where targets might reveal themselves to the sensors aboard the platform, or where intelligence collection vehicles might discover them and relay the information to the aircraft. The ability to persist in hostile airspace reduces the amount of time between identiªcation of a ºeeting target and attacking it, thereby increasing the prompt response of the aircraft. Aircraft that are able to persist in hostile airspace reduce the survivability of exposed enemy

88. Mark Daly, ed., Jane’s Unmanned Aerial Vehicles and Targets, No. 29 (Surrey, U.K.: Jane’s Infor- mation Group, 2007), p. 270. 89. UAVs can remain airborne while the remote crews change over for rest and recuperation. 90. Unless the aircrew can unstrap from their seats, ºight duration should not exceed twelve hours. See Barrie and Butler, “Next-Generation Bomber Sets Stage for ISR Penetrator.” The MQ-9 Reaper can endure for thirty-ªve hours. See Daly, Jane’s Unmanned Aerial Vehicles and Targets, p. 270.

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targets, which means the effectiveness of the adversary’s strategy and operations might be undermined if the targets must remain concealed to avoid destruction. The U.S. use of B-1B bombers in Iraq in 2003 exempliªed the operational beneªt of persistence. Due to their extended dwell times in benign airspace and ability to carry 48,000 pounds of bombs, the B-1Bs were useful in on-call, roving bombing efforts.91 In the long term, however, it might become more difªcult for even aircraft designed for stealthy operations to persist in hostile airspace protected by advanced air-defense systems. To ensure defense penetration and persistence, B-2A bombers operate primarily at night, and in 1991 U.S. F-117 stealth aircraft had supplemental standoff jamming to assist their missions over Iraq.92 weapons delivery accuracy. Since the Vietnam War, U.S. aircraft- delivered munitions have enjoyed signiªcant advances in accuracy. Some aircraft-delivered precision-guided munitions, especially laser-guided bombs and the JDAM, have a CEP of 3–5 meters.93 In contrast to cruise and ballistic missiles, laser-guided bombs and JDAMs are relatively inexpensive because they consist of guidance kits added to free-fall bombs. The JDAM tail-kit, for example, uses an inertial reference unit aided by location and time signals from at least four GPS satellites.94 Although the use of laser-guided bombs is limited to clear weather to maxi- mize delivery accuracy, JDAMs can be employed in any weather condition for maximum effectiveness. Furthermore, JDAMs are true ªre-and-forget weapons systems: once released from the aircraft, they can travel independently to their separate targets without human intervention. throw weight. The throw weights of deployed armed UAVs are sufªcient for defeating near-term PGS targets. The MQ-9 Reaper, for example, can lift 3,800 pounds of ammunition. In addition, the throw weights of deployed manned aircraft are superior to available alternatives for defeating hard and deeply buried targets, and long-term armed UAVs will likely have as high a throw weight and combat radius as manned bombers. For example, the B-2A bomber has a throw weight of 40,000 pounds; it can carry four 5,000-pound

91. Adam J. Hebert, “The Long Reach of the Heavy Bombers,” Air Force Magazine, Vol. 86, No. 11 (November 2003), pp. 24–29. 92. Grant, The Radar Game, pp. 39, 51. Such limitations could reduce effectiveness in time-sensitive missions. 93. Daly, Jane’s Unmanned Aerial Vehicles and Targets, pp. 268–271; and Lennox, Jane’s Strategic Weapon Systems, pp. 182–183, 196, 209, 213. 94. Barry D. Watts, Six Decades of Guided Munitions and Battle Networks: Progress and Prospects (Washington, D.C.: Center for Strategic and Budgetary Assessments, 2007), pp. 176, 213–214.

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GBU-28 (BLU-113) penetrators in one weapons bay and forty 500-pound GBU- 38 JDAMs in the second bay for a single mission.95 payload ºexibility. Due to their throw weight, manned aircraft have the greatest payload ºexibility of near- and midterm PGS options. Long-term UAVs, however, could be designed to have the same payload ºexibility as manned aircraft. For example, the MQ-9 Reaper’s underwing hardpoints allow for sixteen AGM-114 Hellªre missiles, two Paveway II laser-guided bombs, or the GBU-38 500-pound JDAM, and for mixed loads of these weapons.96 This breadth of payload ºexibility is more than sufªcient for near-term missions against several soft targets. target acquisition. Unlike near- and midterm CBMs, aircraft can acquire targets through onboard and off-board sensors, although cloud cover and smoke would obscure some aircraft onboard sensors. Moreover, the target acquisition capability of UAVs is comparable to manned aircraft. For example, armed UAVs are outªtted with electro-optical and infrared sensors, electronic support measures, multispectral targeting systems sensors, and real-time video data relay to pilots and commanders in remote locations.97 Target acquisition is critical to shortening the kill chain. By mating the intelligence, surveillance, and reconnaissance function to the shooter, aircraft can search for mobile or ªxed targets whose locations are vaguely known in fairly benign airspace. The B-1B bomber, for example, is equipped with an electro- optical/infrared targeting pod for positively identifying ªxed and moving targets from standoff distances. The pod also permits the bomber crew to designate targets for laser-guided bombs, generate targeting coordinates for JDAMs, share real-time video images with combat controllers on the ground to increase the probability of striking the correct target, and assess battle damage.98

summary Overall, near-term and midterm land- and sea-based CBMs would prevail over manned and unmanned aircraft in prompt response, combat radius, and defense penetration (see table 2). CBMs would also have the high weapons delivery accuracy of aircraft-delivered precision-guided munitions. Although prompt response over an intercontinental range would be desirable in some

95. Hunter, Jane’s Aircraft Upgrades. 96. Daly, Jane’s Unmanned Aerial Vehicles and Targets, p. 268. 97. Ibid. 98. Michael Sirak and Marc Schanz, “Air Force World,” Air Force Magazine, Vol. 91, No. 10 (Octo- ber 2008), pp. 16–26.

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Table 2. Technical Evaluation, Notional Near- and Midterm Prompt Global Strike Weapons Delivery Options

Sea-Based Land-Based Armed Conventional Conventional Unmanned Ballistic Ballistic Manned Aerial Attribute Missile Missile Aircraft Vehicle

Prompt responsea Combat radius Weapons delivery accuracy Throw weightb Defense penetration Payload flexibilityb Target acquisition Persistencec Prelaunch survivabilityd

NOTE: Scoring code

Effective Marginally Ineffective Effective aThis assumes that forward-deployed aircraft are available, but sufficient strategic warning lead time for their effective use is not. bWith the exception of physically defeating hard and deeply buried targets, near-term conventional ballistic missiles would have sufficient throw weight and payload flexibility for soft targets. cDepending on the time to the target area and rate of fire for a missile base (or naval vessel), land- and sea-based conventional ballistic missiles might essentially dwell, prepared for launch, outside of hostile territory in order to respond to emerging threats. dIn many situations, the prelaunch survivability of land-based, mobile continental ballistic missiles would be as high as that for sea-based conventional ballistic missiles. In addition, aircraft on alert or sheltered in hardened structures might elude destruction from an enemy attack.

scenarios, mission planners and decisionmakers might seek the throw weight, persistence, payload ºexibility, and target acquisition capability of aircraft to ensure mission success in scenarios involving mobile targets as well as hard and deeply buried targets. As ªgure 1 illustrates, the capabilities of near-term CBMs would have military utility against soft, ªxed targets when forward-deployed aircraft and sufªcient strategic warning lead time for their attacks were not available.99

99. The U.S. Department of Defense deªnition of strategic warning lead time is that time between

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Figure 1. Constructing a Portfolio of Prompt Global Strike Options

NOTE:CBMsϭ conventional ballistic missiles

Against hard and deeply buried targets and mobile targets, however, aircraft capabilities will remain superior in the near- and midterms. Long-term aircraft and CBM options for use against time-critical hard and deeply buried targets and mobile targets will require advanced technologies, such as missile booster propellants for lifting heavier payloads at a smaller rate of cost increase, reentry vehicle deceleration to prevent deforming penetrator weapons carried by CBMs, aircraft stealth and propulsion improvements to increase survivability in hostile environments and response times, in-ºight retargeting for CBM payloads, and improved target acquisition and tracking.

Evaluation of the Case against CBMs: Nuclear Ambiguity

The strongest case against CBMs as a means to close the U.S. prompt global strike gap is the risk of the target state, or a third-party state that detects a missile traveling toward its territory, misinterpreting the ballistic missile ºight as an indicator of nuclear attack and responding with nuclear weapons.100 Critics of some CBM options argue that states with an early warning system to detect missiles in ºight, such as Russia, might not be able to distinguish CBMs from nuclear missiles.101 The condition that underlies this problem is the short deci-

receipt of strategic warning and the beginning of hostilities. DOD Dictionary of Military and Associ- ated Terms, Joint Publication 1-02 (Washington, D.C.: Joint Doctrine Division, J-7, Joint Staff, De- partment of Defense, as amended through May 30, 2008), http://www.dtic.mil/doctrine/jel/ doddict/. 100. For further analysis of this subject, see National Research Council, U.S. Conventional Prompt Global Strike, pp. 3-9, 3-15. 101. Postol, “An Evaluation of the Capabilities and Limitations of Non-Nuclear-Armed Trident

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sion cycle associated with a launch-on-warning doctrine in response to a perceived nuclear missile attack. According to publicly available information, nuclear-armed states have not misinterpreted past combat missions of nuclear-capable U.S. bombers on their periphery, such as ºights outside of Russian airspace in Operations Desert Storm (Iraq, 1991), Enduring Freedom (Afghanistan, 2001–present), and Iraqi Freedom (2003–present), but the decision cycle for assessing and responding to a bomber attack, if detected prior to penetration of friendly airspace, is longer than the time for assessing and responding to a ballistic missile attack prior to weapons impact. If they have a launch-on-warning doctrine and detect seem- ingly hostile ballistic missile ºights, according to CBM opponents, the states may inadvertently launch a nuclear retaliatory strike. Although Russia may not be able to detect incoming missiles all around its periphery, it might repair the suspected gaps in its early warning system in the near future.102 Thus, it behooves analysts to consider a fully operational Russian early warning system when assessing the deployment and use of U.S. CBMs that would ºy over Russia on the way to their targets. It is plausible for Russia to monitor and track one or two U.S. ballistic missiles in ºight toward a target in Southwest Asia and, in the absence of a crisis with the United States, wait to determine if the weapons will detonate over its soil. Although it is improbable in this scenario that Russia would launch a nuclear attack due to the low likelihood that the missiles were the vanguard of a larger U.S. nuclear attack, it was reported that Russian ofªcials brieºy alerted their nuclear forces in response to what was an unarmed Black Brant XII Norwegian-U.S. joint research rocket originating from Norway’s northwest coast in 1995.103

Ballistic Missiles for Short-Time Conventional Strikes”; and Pollack, “Evaluating Conventional Prompt Global Strike,” p. 18. See also U.S. Congress, House of Representatives, “Making Appro- priations for the Department of Defense for the Fiscal Year Ending September 30, 2005, and for Other Purposes,” conference report to accompany H.R. 4613, H.Rept. 108–622, 108th Cong., 2d sess., July 20, 2004, p. 240. 102. Postol, “An Evaluation of the Capabilities and Limitations of Non-Nuclear-Armed Trident Ballistic Missiles for Short-Time Conventional Strikes.” For the view that the gaps in Russia’s radar coverage are overestimated, see Pavel Podvig, “Russian Early-Warning System and the Risk of an Accidental Launch,” paper presented at a meeting of the Center for Science, Technology, and Secu- rity Policy and the American Association for the Advancement of Science, “Conventional Missiles and Early Warning Systems: The Proposed D-5 Trident Conversion and the Impact on Rus- sia’s Early Warning System,” Rayburn House Ofªce Building, Washington, D.C., October 6, 2006, http://cstsp.aaas.org/ªles/pvel.pdf. 103. Center for Nonproliferation Studies, “WMD 411 Chronology 1995” (Monterey, Calif.: Center for Nonproliferation Studies, Monterey Institute of International Studies, 2004), http://www.nti .org/f_wmd411/1995.html; and Postol, “An Evaluation of the Capabilities and Limitations of Non-Nuclear-Armed Trident Ballistic Missiles for Short-Time Conventional Strikes.” Postol suggests that the potential for a single nuclear-armed SLBM to black out Russian early warning radar increases the chances of a nuclear accident, although it does not necessarily mean that Russia

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My conclusion is not that Russia or other nuclear-armed states with missile early warning systems would hastily and disproportionately respond to detection of a few U.S. CBM ºights, but that the ambiguity of ballistic missile ºights could raise the risk of an inadvertent nuclear response under the following set of conditions: (1) heightened political-military tensions between the United States and the nuclear state; (2) poor military and diplomatic communications between the states and lack of notiªcation about the CBM ºights; (3) lack of distinguishing characteristics between the CBMs and nuclear-armed missiles (e.g., basing modes and ºight trajectories); and (4) lack of training for personnel in the nuclear state’s early warning and attack assessment chain of command for dealing with limited-scale CBM ºights. There are potential measures to mitigate the nuclear risks associated with CBMs.104 First, a coastal basing scheme, possibly at Vandenberg and Patrick Air Force Bases in California and Florida, respectively, would geographically separate CBMs from their nuclear counterparts based in the interior of the United States. This measure, however, would not prevent the United States from surreptitiously arming the missiles with nuclear warheads. A second measure is a distinct concept of operations for CBMs to further differentiate them from nuclear-armed, silo-based ICBMs. Suggested concepts of operations include mobile launchers, horizontal emplacement in earthen berms, or above ground on launch pads, as well as observable differences between CBMs and nuclear ICBMs, such as variations in the sizes of the booster stages. Third, to avoid miscalculations, a collection of measures between the United States and key states could be institutionalized to build transparency in CBM operations, such as continuous video monitoring of CBMs to allow for surveillance of payload removal and replacement, short-notice inspections similar to those exer- cised under the Strategic Arms Reduction Treaty, and shared early warning.105 In addition, there could be prior notiªcation of operational missile launches and a hotline for leaders to discuss ambiguous indicators that could potentially drive miscalculations. For example, U.S. ofªcials could confer with their

would take actions to launch their nuclear forces. (I would add that inoperable radars would not prevent a nuclear response.) Moreover, SLBMs launched from the northern portions of the Atlan- tic and Paciªc Oceans toward Southwest Asia could black out Russian northern tier radar sites, thereby preventing Russia from detecting U.S. ICBM ºights. SLBMs launched from the southern areas of the two oceans toward Southwest Asia, however, would not be able to create the same effect. Russia may detect CTMs launched from the Southwest Paciªc that ºy toward Southwest Asia. 104. Amy F. Woolf, Conventional Warheads for Long-Range Ballistic Missiles: Background and Issues for Congress, CRS Report for Congress (Washington, D.C.: Congressional Research Service, Library of Congress, May 2008), Order Code RL33067, pp. 22–25; and Flory, “Statement Regarding Global Strike Issues.” 105. For discussion of continuous monitoring of CTM tubes aboard submarines, see National Re- search Council, U.S. Conventional Prompt Global Strike, p. H-2.

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counterparts in Russia and China to notify them of CBM operations against targets that require ºying over those countries. Fourth, delivery vehicles capable of ºying shaped trajectories (e.g., performing cross-range maneuvers) might enable weapons to avoid ºying over nuclear-armed states and popu- lated areas. Another possible measure to mitigate risks entailed in ballistic missile ºights is to base CBMs outside of the continental United States. An ideal location would be U.S. territorial islands, such as Guam, to greatly reduce the risk of missile overºight.106 Guam-based CBMs might not have to transit over Russia unless targets were in Europe or parts of North Africa. Given the short ºight times for Guam-based CBMs to reach the Asian landmass, however, this option might generate strong political opposition from China.107 Alternative locations should be studied as potential mitigating measures. The CTM, given that it would be based outside of the continental United States, would also mitigate concerns with CBMs ºying over nuclear-armed states.108 Moreover, the other mitigation measures could be employed along with forward basing schemes to reduce the chance of misinterpretation. How much assurance is enough? Russia might always suspect the worst- case scenario: replacement of conventional warheads with nuclear warheads. Discussions with Russia, however, would permit U.S. policymakers to scale the mitigation measures to a sufªcient level of assurance. Russia might never be completely satisªed, yet it is not plausible that it would launch a nuclear attack if the United States took several measures to clarify the character and in- tent of a handful of CBM ºights over Russia. Assuring Russia and other nuclear-armed states with respect to long-term PGS options, such as large- scale CBM strikes, would be more challenging and likely require abstaining from ºying over the states altogether. CBMs based in the continental United States and at forward locations that carry boost-glide vehicles, ideal for shaped trajectories, would mitigate the risk of ambiguous warning.

Conclusion

The United States should deploy conventional ballistic missiles, in the near term, in support of the prompt global strike mission. The analysis of capabilities shows that ballistic missiles can deliver a prompt conventional response

106. See the Forward-Based Global Strike option in Woolf, Conventional Warheads for Long-Range Ballistic Missiles, p. 28. 107. China might perceive U.S. ballistic missile bases near its territory as inherently destabilizing, as the United States judged Soviet missiles in Cuba in 1962. 108. Sea-based missiles, compared to land-based missiles, could more easily avoid the risk of ºying over and being detected by nuclear-armed states, depending on target and launch locations.

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within minutes from receipt of an attack order that would be optimal for defeat of soft, ªxed targets. The limitations of near-term CBMs, however, would make them ineffective against mobile targets as well as hard and deeply buried targets. In the near term, the U.S. Navy’s Conventional Trident Modiªcation proposal is the most cost-effective prompt global strike weapons system that will enable the most risk mitigation leverage for the United States. Given that conventional Trident D-5 SLBMs would occupy only two out of twenty-four launch tubes on the Ohio-class submarines that carry such missiles, U.S. tax- payers will not bear the cost of an entire submarine committed solely to ensuring the survival of CBMs. If CTM were deployed, then military planners should ensure that the submarines launch their missiles from areas of the ocean that would obviate the need to travel over or near nuclear-armed states with missile warning systems to avoid the chance of miscalculation. Because circumstances would not always permit missile ºights to remain undetected by nuclear-armed states, the United States should work to implement other mitigation measures. The analysis suggests several policy recommendations and avenues for future study. First, if a requirement for CBM strikes beyond a handful of targets grows more signiªcant, then analysts will have to more fully assess the trade- offs between expanded CTM deployment and land-based CBM deployment at forward operating locations. Forward-deployed, mobile or soft-site operations are ideal for expanded PGS missions because they would be fairly survivable in most locations and would help to mitigate overºight concerns. These options would also defeat ºeeting targets more promptly than CBMs based in the continental United States. In addition, though further analysis is required to assess the relative ªnancial costs of midterm CBM options, increasing the number of CTM missiles aboard strategic nuclear submarines would increase the ªnancial costs of CBM deployment and remove nuclear weapons from highly survivable platforms, which might undermine U.S. nuclear deterrence. The strongest rationale for expanding the use of CBMs would be defeating sophisticated anti-access and area-denial threats. U.S. aircraft and many standoff missiles designed for stealthy defense penetration are capable of circum- venting and defeating the threat, but this capability might grow relatively weaker. Because the primacy of low-observable, stealthy aircraft and standoff missiles over air-defense systems should not be assumed to hold far into the future, it behooves the defense community to conduct a functional net assessment of foreign advances in area-denial technology vis-à-vis U.S. defense penetration capabilities. The ªndings of this future study could help determine midterm and long-term requirements for PGS weapons systems. Second, given that the large-scale use of CBMs would likely contribute to

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greater risks for miscalculation between nuclear-armed states, U.S. policymakers should support this option only from sites outside the continental United States that could more easily avoid generating concerns over nuclear ambiguity. This recommendation would change, however, if the United States developed CBMs with extended range and reentry vehicles capable of cross-range maneuvers. These capabilities would allow strike missions to follow routes that circumvent nuclear-armed states when launched from the continental United States. Third, for the long term, the United States should continue investing resources into research and development of improved ballistic missile technologies and payloads. If it becomes feasible to build improved boosters and reentry vehicles, such as the hypersonic glide vehicle, that can accurately deliver heavy payloads comparable to aircraft in a cost-effective manner, then CBMs would become more useful against hard and deeply buried targets. Fourth, to cover the emerging target set and compensate for potential long- term capabilities gaps, the United States should build a portfolio of PGS options encompassing CBMs and long-range, stealthy, unmanned aircraft. Moreover, in case physical destruction of hard and deeply buried targets using CBMs remains infeasible, analysts should continue studying the requirements for functionally defeating such targets. These requirements will encompass technological capabilities and tactics. Fifth, if CBMs cannot use GPS assistance for greater weapons delivery accuracy, it then follows from the analysis that the United States should focus more resources on using stealthy, armed UAVs for the PGS mission. UAVs can carry the same payloads as manned aircraft but have longer ºight endurance. To avoid prolonged violations of sovereign airspace, the UAVs might have to loi- ter outside, as their remote pilots await execution orders. This option would put a premium on forward-based, long-range UAVs. This would not be the optimal option for PGS missions, but it would be the best option if CBMs do not achieve the required accuracy. In the long term, aircraft capable of hypersonic speeds might be able to execute PGS missions from the continental United States. Finally, to enhance U.S. conventional, long-range strike capabilities and pre- pare for technological breakthroughs, U.S. policymakers should consider rene- gotiating articles of arms control treaties that constrain CBM options. Soft-site launch pads, for example, would beneªt CBM operations in Guam and other forward operating locations. This treaty option must be weighed, however, against the costs of opening up strategic options for other states.

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