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Nuclear Deterrence in the 21st Century: The Role of Science and Engineering Joseph C. Martz and Jonathan S. Ventura Los Alamos National Laboratory Albuquerque, New Mexico For five decades after the Second World War, the role of nuclear weapons in the U.S. defense posture was largely to deter the Soviet Union from attacking the United States, its allies, and friends. Almost as important was the nuclear umbrella (security assurances) the United States provided to discourage (dissuade) non- nuclear nations from pursuing nuclear weapons. These two roles were critical to the formulation of the Nonproliferation Treaty. When the Cold War ended with the sudden collapse of the Soviet Union, the purpose of nuclear deterrence was fundamentally changed. Although the United States continued to retain nuclear weapons as instruments of retaliation, the dynamics of deterrence were evolving. In the future, we will need substantially fewer deployed weapons to address a variety of potential adversaries. Unlike the security challenges of 50 years ago, 21st-century challenges are multipolar and often asymmetric. However, a few key countries still have substan- tial nuclear arsenals and active, growing nuclear weapons programs that threaten vital U.S. interests. Thus maintaining a credible U.S. nuclear deterrent in the eyes of our allies and our adversaries, as well as supporting the goal of nonproliferation, will continue to be critical to U.S. national security. Overlaid on this national security backdrop are concerns about the effects of 141

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142 FRONTIERS OF ENGINEERING a growing world population on climate, food, and energy—which greatly compli- cate the security challenges facing policy makers today. This changing paradigm requires that the United States take additional measures (1) to assure our allies that we are still a trusted security partner and (2) to deter potential adversaries from taking aggressive action that could threaten global stability. Every U.S. president since Truman has affirmed the role of nuclear weapons as a supreme deterrent and protector of last resort of U.S. national security interests. Recently, President Bush called for a “…credible deterrent with the lowest possible number of nuclear weapons consistent with our national security needs, including our obligations to our allies.” How can this be achieved? Can we continue on a path of nuclear reductions while maintaining the national security benefits of nuclear deterrence? Science and engineering will play a key role in the new paradigm for nuclear deterrence, “capability-based deterrence.” CAPABILITY-BASED DETERRENCE Capability-based deterrence is based on the principle that an agile, repeatedly demonstrated capability to develop and produce deployable nuclear weapons will greatly strengthen the deterrent and enable meaningful reductions in the size of the total stockpile. In this scenario, the country can rely, in part, on a working weapons complex that could deliver limited numbers of nuclear weapons should the situation require rather than on large numbers of reserve or deployed warheads for contingency purposes. The new strategy would provide the benefits of deterrence while enabling us to meet some key goals, such as reducing the stockpile of nuclear weapons. Indeed, the head of the National Nuclear Security Administration (NNSA) stated in December 2007—when he proposed a transformation of the nuclear weapons complex—that “the United States’ future deterrent cannot be based on the old Cold War model of the number of weapons. Rather, it must be based on the capa- bility to respond to any national security situation, and make weapons only if necessary.” This adoption of capability-based deterrence would represent a shift in the emphasis of our nuclear policy. The role of science and engineering would become a critical element in establishing the agility and confidence necessary for this strategy to work. The principal elements of capability-based deterrence are (1) the weapons themselves (albeit fewer and potentially designed to meet the specific require- ments of this strategy); (2) the design, development, and manufacturing elements of the weapons complex. It is not only the capabilities of our military forces that Remarks by the President to Students and Faculty at National Defense University, Fort Lesley J. McNair, Washington, D.C., May 1, 2001.   emarks by Thomas D’Agastino on the Introduction of the Complex Transformation PEIS, U.S. R Department of Energy Headquarters, Washington, D.C., December 17, 2007.

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NUCLEAR DETERRENCE IN THE 21ST CENTURY 143 assure our allies and deter potential adversaries; it is also our capability to sustain and modernize our forces, while demonstrating the ability to respond rapidly to new or emerging threats. The notion of capability-based deterrence is not completely new. It was included in the Bush administration’s “new strategic triad” concept and was emphasized in the administration’s 2001 Nuclear Posture Review (NPR). It was also part of the Clinton administration’s NPR in 1994 and was a principle in the founding of the Stockpile Stewardship Program. This science-based program of experimentation, improved diagnostics, and greatly increased computational capabilities gave us the tools to assess and redress problems in our management of the stockpile. Research conducted at new experimental facilities has improved our understanding of the physics of weapons performance and thus contributed to the program’s remarkable technical success, which has increased confidence in our ability to transition to capability-based deterrence. ENABLING A CAPABILITY-BASED DETERRENT Timeliness and agility are critical elements of this new strategy. We must be able to detect and respond to a potential adversary quickly enough to counter any provocative act. The need for timeliness is an interesting contrast to our Cold War posture. In decades past, we had to be ready to respond to a provocative act on a moment’s notice. Thus we had bombers on constant standby, intercontinental missiles on hair-trigger alert, and submarines on continuous patrol in the great oceans. Our answer to the timing question then was in minutes. Today, a threat that might require a response of such a large arsenal may not become manifest for several years. Indeed, in an environment of stockpile reductions—both the United States and Russia have reduced their arsenals by more than 90 percent from their Cold War peaks—we no longer need the large nuclear forces that characterized the Cold War. If an adversary decided to restart an arms race, it would require a large investment on their part, and, in principle, sufficient time for the United States and its allies to respond. In essence, the change in strategy would mean moving from the deterrence afforded by large numbers of deployed and reserve weapons to deterrence pro- vided by a smaller number of deployed weapons and a robust and agile infrastruc- ture and capability. This strategy could potentially provide many of the benefits of nuclear deterrence while enabling us to continue to reduce our stockpile. The promise of this strategy—the ability to provide an agile, diverse response to many threats—would provide us with an advantage we did not have when we relied solely on a stockpile of Cold War-optimized, high yield-to-weight weap- ons. Science and engineering will be key to enabling the United States to become an agile responder, because a capability-based deterrent must be grounded in science.

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144 FRONTIERS OF ENGINEERING The challenge is to develop and demonstrate a steady-state capability to execute a complete cycle of warhead design, certification, development, and pro- duction in a three-to-seven-year time frame. This cannot be done with our current very outdated and archaic production complex and 1970s-era design practices. The NNSA proposal for a transformation of the nuclear weapons complex that will increase U.S. agility and inspire more confidence is not entirely theoreti- cal. Recent developments in the NNSA complex have demonstrated the viability of some key elements of this strategy, most notably a few recent stockpile life- extension program activities, as well as the reliable replacement warhead (RRW) feasibility study. THE RELIABLE REPLACEMENT WARHEAD In the RRW study, laboratory design teams were able to provide highly mature designs in less than 12 months—largely thanks to modern engineering and design tools created under the Stockpile Stewardship Program. In addition, the laboratories built prototype demonstration hardware and conducted limited, nonnuclear proof tests of their designs within 18 months. Note that in the 1980s, this level of design maturity required several years. These proof tests exercised a portion of the production complex and provided a concrete example of the agility and timeliness that would be possible. In addition, RRW designs were based on the “relaxation” of a Cold War objective—maximizing yield-to-weight ratios. The RRW designs instead increased performance margins and backed away from known failure modes of the legacy stockpile. Increased performance margins coupled with advances in weapons sci- ence will provide high-confidence in certification of these RRW designs without nuclear testing. In the future, advanced features could be included in the designs to improve safety, security, and use control in the warhead and also improve the efficiency of manufacturing operations. SUMMARY A movement toward an active, fully functional, demonstrated capability- based deterrence program could help the nation meet its future policy objectives: further reductions in the size of the stockpile, certification of our nuclear deterrent without nuclear testing, and advancing compliance with Article 6 commitments under the Nuclear Nonproliferation Treaty. Two key enablers of an articulated capability-based deterrent are the transfor- mation of the weapons complex (as proposed by NNSA) and the adoption of many of the concepts and approaches demonstrated in the RRW project—all of which were made possible by the science and engineering methods and tools developed under the Stockpile Stewardship Program. Although the U.S. government has proposed that we move toward a “…credible

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NUCLEAR DETERRENCE IN THE 21ST CENTURY 145 deterrent with the lowest-possible number of nuclear weapons consistent with our national security needs,” we can only move in that direction in an environment in which our security is maintained, our allies are assured of our commitments, and our adversaries are dissuaded and deterred. However near or remote a world free of nuclear weapons may be, a capability-based deterrence to meet today’s threats can facilitate reductions in the stockpile while maintaining our security and limiting technical risks. RECOMMENDED READING Shultz, G.P., W.J. Perry, H.A. Kissinger, and S. Nun. 2008. Toward a Nuclear Free World. Editorial in the Wall Street Journal, January 15, 2008. Lewis, J. 2008. Minimum deterrence. Bulletin of the Atomic Scientists 64 (3): 38–41. Bunn, M.E. 2007. Can deterrence be tailored? Strategic Forum 225: 1–8.

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