Cole J. Harvey
Research Associate, The James Martin Center for Nonproliferation Studies
Nuclear Stockpile Modernization: Issues and Background
President Barack Obama has committed the United States to a series of major nuclear disarmament and nonproliferation measures, including the negotiation and ratification of a new strategic arms reduction treaty with Russia, ratification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), and a nuclear posture that "reduce[s] the role of nuclear weapons in our national security strategy," with the ultimate goal of a "world without nuclear weapons." As the United States considers shrinking its nuclear weapons stockpile and committing to a ban on nuclear testing, government officials want to ensure that the remaining weapons will provide a credible deterrent against potential adversaries. In a speech outlining his disarmament goals in Prague on April 5, 2009, Obama also affirmed that so long as nuclear weapons exist the United States will maintain a "safe, secure and effective arsenal." This dual commitment, to reducing nuclear weapons while maintaining a reliable nuclear deterrent has triggered a debate about the degree of "modernization" the remaining U.S. weapons should undergo to ensure confidence that the weapons would work if used.
In a July 1, 2009 "letter to the editor" published in the Financial Times, Senator John Kyl (R-Ariz.) framed the issues in dispute, writing that, "Every nuclear weapons power-with the exception of the US-is currently modernising its nuclear weapons and weapons delivery systems…Yet the US continues to permit its nuclear forces to atrophy and decline." Later in 2009, all 40 Republican senators at the time, along with independent senator Joe Lieberman (I-Conn.), tied U.S. nuclear weapon modernization to the ratification of a new U.S.-Russian arms control agreement in a December 15 letter to Obama. The senators wrote that the further reductions in the U.S. nuclear arsenal would be acceptable only if accompanied by "a significant program to modernize our nuclear deterrent." In the letter, the senators called for "funding for a modern warhead that includes new approaches to life extension involving replacement, or possibly, component reuse." Since Obama would need 67 votes in the U.S. Senate to obtain consent for the ratification of the new arms control pact, the letter appeared to leave the president little choice but to accommodate the demands of at least nine of its signers. The administration's proposed budget for fiscal year 2011 would increase funding for the stockpile, perhaps in a bid to win such senators' support (See "The nuclear stockpile and the fiscal year 2011 budget request," below).
The United States is not currently pursuing a new warhead design, as Congress has terminated a Bush administration initiative known as the Reliable Replacement Warhead. Nevertheless, the argument that the United States is not currently modernizing its nuclear arsenal is not completely accurate, as it disregards the extensive and expensive efforts the United States takes to monitor and refurbish both warheads and delivery systems. However, there is a spectrum of additional responses the United States might take to further ensure the reliability of its nuclear stockpile into the future, including the development and production of a new warhead. Embarking on such a program would entail political costs, however, that, some believe, could jeopardize U.S. nonproliferation priorities.
The United States produced its last new nuclear weapon in 1990 and ceased underground nuclear testing in 1992. As the existing warheads age, components can change and deteriorate. A 1983 report for the Department of Energy sounded a distinctly alarmed note, observing that,
"Certain chemically reactive materials are inherently required in nuclear weapons, such as uranium or plutonium, high explosives, and plastics. The fissile materials, both plutonium and uranium, are subject to corrosion. Plastic-bonded high explosives and other plastics tend to decompose over extended periods of time…portions of materials can dissociate into simpler substances. Vapors given off by one material can migrate to another region of the weapon and react chemically there… Materials in the warhead electrical system…can produce effluents that can migrate to regions in the nuclear explosive portion of the weapon…The characteristics of high explosives can change with time…Vital electrical components can change in character…"
The introduction of more modern warhead designs for weapons added to the stockpile since 1983 and the further study of aging weapons have mitigated many of these problems, however. An independent 1987 report for Congress found that the problems cited in the 1983 report had "little if any relevance to the question of maintaining the reliability of the stockpile of nuclear weapons that exist[ed] in 1987." More recently, an independent scientific report in 1999 found that, "Until now, clear evidence of warhead deterioration has not been seen in the enduring stockpile, but the plans for remanufacture still assume that deterioration is inevitable on the timescale of the old, arbitrarily defined 'design lives'."
In 2006, a panel of scientists concluded that the plutonium primaries, or "pits," of thermonuclear weapons — the atom-bomb triggers — aged much slower than previously thought. The panel wrote that:
"…there is no degradation in performance of primaries of stockpile systems due to plutonium aging that would be cause for near-term concern regarding their safety and reliability. Most primary types have credible minimum lifetimes in excess of 100 years as regards aging of plutonium; those with assessed minimum lifetimes of 100 years or less have clear mitigation paths that are proposed and/or being implemented."
Though the plutonium core may resist aging for many decades, a nuclear warhead is a complex device with many components ( the B61 nuclear bomb, for example, is made of more than 5,900 parts ). In the absence of underground testing, Congress established the Stockpile Stewardship Program (SSP) in 1994 to monitor and refurbish aging weapons, and to certify the reliability of the nuclear stockpile.
In order to maintain the reliability of the nuclear stockpile, the Stockpile Stewardship Program monitors weapons for signs of aging (stockpile surveillance); conducts computer simulations and non-nuclear tests in order to scientifically verify the continued reliability of weapons in the stockpile (assessment and certification); and replaces aging components of weapons before returning them to the field (weapon refurbishment). The program relies on the data gathered from the more than 1,000 nuclear tests conducted by the United States through 1992, and, when refurbishing warheads, adheres as closely as possible to the original design specifications of tested weapons.
Each year, 11 warheads of each type employed by the United States are taken from the stockpile and examined for signs of "corrosion, gases, and other evidence of deterioration." One of the 11 undergoes destructive testing, while the remaining 10 are returned to the stockpile after examination.
Of the thousands of components of a nuclear warhead, nearly all can be tested without violating the United States' moratorium on nuclear testing. Replacements for these components, such as the arming system, can be subjected to rigorous testing and evaluation. As a result, they can be upgraded to incorporate "more advanced electronics or safer materials." The nuclear explosive package-those portions of the warhead that actually explode-cannot be empirically tested all the way to a nuclear chain reaction without violating the moratorium on nuclear tests. However, the fissile material used in the core of the weapon can be removed, and replaced with a non-fissile radioactive material such as uranium-238. The modified package can then be fired to test its components without generating a nuclear explosion. Such tests have been regularly conducted at U.S. weapons labs.
Weapon refurbishment is carried out through Life Extension Programs (LEP) for individual systems. Currently, the National Nuclear Security Administration (NNSA) is conducting an LEP for the W76 warhead, deployed atop Trident missiles on the U.S. Navy's nuclear-armed submarines. The W76 LEP is expected to extend the life of the warhead by 30 years, according to the NNSA, by "refurbishing the nuclear explosive package, the arming, firing, and fusing system, the gas transfer system, and associated cables, elastomers, valves, pads, cushions, foam supports, telemetries, and other miscellaneous parts."
In 2009, the NNSA completed an LEP for the B61-7 and B61-11 nuclear bombs, extending their service lives by 20 years "by refurbishing the canned subassembly and replacing the associated seals, foam supports, cables and connectors, washers, o-rings, and limited life components." The two versions of the B61 are designed to produce variable explosive yields and could be used as tactical or strategic weapons. The B61-11 is the only nuclear weapon in the U.S. arsenal with a so-called "bunker-busting" capability, as it can penetrate a few feet into the earth before detonating.
The Air Force is also replacing the aging W78 warheads used on Minuteman III intercontinental ballistic missiles with the newer W87 warhead. The W87 first entered the stockpile in 1986.
In addition to maintaining the warheads themselves, the U.S. government has also invested heavily in upgrading the missiles and bombers that carry them.
The Air Force has implemented several programs to upgrade and modernize the 450 Minuteman III missiles that constitute the U.S. ICBM fleet. It has replaced the solid rocket fuel in more than 80% of the missiles, in order to extend the life of the rocket motors. Engineers have also replaced the missiles' guidance sets, in order to increase their reliability, and are replacing the post-boost engines to ensure their reliability to the year 2020. The Air Force plans to continue modernizing and refurbishing the Minuteman III through 2025 or beyond. Ambassador Steven Pifer, formerly the senior director for Russia, Ukraine and Eurasia on the National Security Council under the Clinton administration, noted the extensive modernization of the missile, saying that, "When they retire the last Minuteman III in 2030, it may have three of the original bolts on it from 1970, but it's going to be a very different missile."
Similarly, the U.S. Navy has begun a life-extension program for its Trident II missiles, to match the service lifetimes of the Trident submarines, whose retirement is to begin in 2027.
The United States currently fields two nuclear-capable bombers, the B-2 "stealth" bomber and the B-52. The B-2 is a relatively modern aircraft, having become operational in 1997. Nevertheless, the Air Force is currently upgrading its radar and satellite and digital communications capabilities. The B-52 is a much older aircraft, having first entered service in 1955. However, modernization of the B-52 will allow it to remain in service beyond the year 2040. Representatives of the Air Force testified before Congress in May 2009 that the B-52 has been modified to incorporate satellite and "secure wideband high data rate" communications, advanced targeting capabilities, and computer upgrades.
Since the conclusion of the Cold War, the U.S. approach to weapon modernization has been to closely monitor aging weapons and refurbish them as necessary. A competing proposal to bolster the credibility of the U.S. nuclear arsenal in the absence of nuclear testing, the Reliable Replacement Warhead (RRW) program, was authorized in detail in the National Defense Authorization Act for fiscal year 2006. In it, Congress mandated that the Department of Energy begin designing a modern warhead that would "increase the reliability, safety, and security of the United States nuclear weapons stockpile." Rather than rely exclusively on long-term life extension for existing warheads, the program called for the design and production of a new nuclear warhead without the resumption of underground testing.
The program won the support of the George W. Bush administration. In a 2008 report mandated by Congress, the Departments of Energy and Defense wrote that, "It is time for the United States to seek an alternative to the current strategy of extending the lives of legacy warheads indefinitely," and argued that, "The United States must initiate and invest in the RRW program now-so there will be no disconnect between today's credible deterrent and the one required for the future." The RRW initially received a warm welcome in Congress, which appropriated $25 million in fiscal year 2006 followed by $36 million in fiscal year 2007.
Enthusiasm for the RRW waned in the following years, however. Some in Congress felt that the weapons complex had gone beyond the intent of the legislation authorizing the RRW. The Congressional Research Service has counted 20 goals for the program elaborated at various points of its development. Former representative David Hobson (R-Ohio), the chair of the House Appropriations Subcommittee on Energy and Water who helped create the language that began the RRW program, has said that, "I wanted to make sure that nobody could play around with these things and come up with new capabilities. You just knew they wanted to." Funding for the program was cut off in fiscal year 2008, pending "a new strategic nuclear deterrent mission assessment for the 21st century."  Congress also declined to fund the RRW in fiscal year 2009 and, in the defense authorization bill for fiscal year 2010, voted to rescind the authorization for the program entirely.
While the RRW is effectively dead, the idea of a "modern warhead" for the U.S. nuclear force is very much alive, as the letter sent by 41 senators to President Obama indicates. As noted, the Obama administration will not be able to win ratification of a new strategic arms control treaty with Russia without satisfying at least nine of the senators who signed the letter demanding funding for a modern warhead. The debate over the continued reliability of the stockpile will only intensify as the administration moves to ratify the CTBT (See NTI issue briefs on the CTBT and related topics).
Reliability. Proponents of a new warhead argue that a modern design is essential to ensure the reliability of the stockpile in the future, as life extension programs will ultimately introduce sufficient changes to the tested design that warhead failure becomes a distinct possibility. The Congressional Commission on the Strategic Posture of the United States, while not endorsing a new warhead outright, echoed this concern in its 2009 report, writing that:
"The possibility of using [LEPs] to extend the life of the current arsenal of weapons indefinitely is limited… The process of remanufacturing now underway introduces some uncertainty about the expected operational reliability of the weapons. So far at least, the directors of the weapons laboratories have been able to certify that they retain confidence in the remanufactured (and other stockpiled) weapons. But there are increasing concerns about how long such confidence will remain as the process of re-inspecting and remanufacturing these weapons continues. Indeed, laboratory directors have testified that uncertainties are increasing."
This argument lost credibility, opponents charge, following a 2009 study by the independent JASON panel of scientists, which found "no evidence that accumulation of changes incurred from aging and LEPs have increased risk to certification of today's deployed nuclear warheads." The report concluded that, "Lifetimes of today's nuclear weapons could be extended for decades, with no anticipated loss in confidence, by using approaches similar to those employed in LEPs to date." Combined with the JASONs' finding that the plutonium cores of nuclear weapons are usable for a century or more, the panel's work indicates that life extension programs can ensure the reliability of the nuclear stockpile for many years into the future, though not necessarily indefinitely.
Allows for deeper reductions in the stockpile. The United States currently maintains a large reserve of 2,500 non-deployed warheads as a hedge against an unexpected technical failure or loss of confidence in its deployed warheads. If the United States builds a new warhead in which it has greater confidence, supporters argue, it could permit larger numbers of warheads to be dismantled.
Maintains the technical skills of the nuclear weapons complex. The generation of nuclear weapons scientists and engineers with experience garnered during the era of warhead design and nuclear testing is diminishing. In testimony before Congress in February 2008, NNSA Administrator Thomas D'Agostino urged support for the RRW, saying that it provides:
"…a critical opportunity to ensure the transfer of nuclear design and engineering skills from the generation who honed these skills with nuclear testing to the generation who will replace them. These skills are absolutely vital to the nation, not just for sustaining our deterrent but in such areas as nuclear counterterrorism which will become even more important in the future. In a few years, nearly all of the older generation will be retired or dead. Without this opportunity coming at this time (and not five years hence), we would not be able to sustain key capabilities."
Benefits to extended deterrence. The United States provides "extended deterrence" to allies in Europe and Asia, pledging to defend those countries with U.S. nuclear weapons if necessary. Extended deterrence, the argument goes, has convinced those states to forego their own nuclear weapons and to rely instead on the United States. Proponents of a new warhead design argue that a smaller U.S. nuclear arsenal composed of aging weapons could cause allies to lose confidence in the protection of the American nuclear umbrella and to embark on their own nuclear weapons programs. Opponents respond that the U.S. arsenal is certified to be reliable by the Secretaries of Energy and Defense each year, and independent scientific analyses have found that the reliability of the arsenal can be maintained for many years through monitoring and refurbishment (See "Aging in Nuclear Weapons," above).
Opponents of a new warhead design warn of steep international political costs should the United States reopen nuclear weapon production, imperiling various nonproliferation measures that are in the United States' interest.
Loss of credibility on nonproliferation issues. Opponents argue that if the United States resumes development and production of nuclear weapons, it will cede substantial credibility as it presses for a stricter international nonproliferation regime or tries to roll back nuclear-weapons related developments in Iran and North Korea. Production of new warheads would almost certainly be taken as an explicit endorsement by the United States of the security benefits and long-term usefulness of nuclear weapons. It could also be seen as a major set-back for the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), under which the United States pledged to "pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament."
Such a loss of credibility could have consequences apart from diminishing the prospects that other states will apply pressure on the Iranian and North Korean nuclear programs. It could seriously jeopardize important nonproliferation measures that the United States is eager to achieve by international agreement-such as wider application of the International Atomic Energy Agency's (IAEA) Additional Protocol (a voluntary agreement that expands IAEA access to information and sites to confirm declared-and detect undeclared-nuclear activities), more international oversight of the nuclear fuel cycle, and tougher export controls. States may be unwilling to make such expanded commitments to nonproliferation if they view the United States as making an expanded commitment to nuclear arms. The ambassador of Sweden, a prominent "middle power" on issues of disarmament and nonproliferation, made this point to the Conference on Disarmament in February 2006, saying:
"If development of nuclear weapons continue [sic], some may become inclined to disregard calls to forgo the possibility of building up their own nuclear arsenals or at least to be less supportive of non-proliferation efforts. We have recently experienced the strain this has put on the NPT."
This strain was highlighted in a working paper at a 2009 meeting on the states-parties of the NPT, submitted by the Group of Non-aligned States-a large bloc of Asian, African, and South American countries. In it, the group stated that "the development of new types of nuclear weapons…and the lack of significant progress in diminishing the role of nuclear weapons in security policies undermine disarmament commitments and work counter to the letter and spirit of the Treaty."
Expansion of the nuclear weapons complex. Constructing a new warhead will require substantial investments in the U.S. national weapons laboratories and production facilities. Where proponents of a new warhead see the transmission of technical knowledge to a new generation of weapons experts, opponents see a very visible and expensive demonstration of U.S commitment to a nuclear weapons arsenal in the long term. Such investments will only further erode the U.S. position on nonproliferation in the international community, they argue.
Possibility of a return to testing. Opponents of a new warhead also emphasize that all of the warhead models currently in the stockpile were tested before the testing moratorium began in 1992. They argue that confidence in a new warhead design that deviates in any way from the tested physics packages of older warheads might diminish over time, which could lead to increased pressure on U.S. leaders to carry out a nuclear test. They also argue that the military will be reluctant to deploy any new weapon that has not been tested. Even in the absence of a CTBT, resumption of nuclear testing by the United States would be an international relations crisis, likely prompting tests by other nuclear powers and severely straining the current disarmament and nonproliferation regime. Opponents argue that the risk of shifting the U.S. arsenal toward an untested warhead design are too great, particularly if life extension programs for existing warheads can ensure the reliability of the stockpile for many years to come.
The Congressional Commission on the Strategic Posture of the United States wrote that these concerns could be mitigated. "The Commission is satisfied that the risks of a return to nuclear testing to support the refurbishment and modernization program could be made minimal," the 2009 report said. The Commission also expressed its belief that the U.S. nonproliferation agenda would not be jeopardized by the production of a new warhead, so long as its development did not alter three aspects of current U.S. policy: no production of fissile material, no nuclear tests, and no new military capabilities.
The National Defense Authorization Act for fiscal year 2010 ended the authorization for the Reliable Replacement Warhead program, and replaced it with a program of "stockpile management." The stockpile management program neither endorses nor excludes the possibility of a new warhead for the United States arsenal. Instead, it directs the Secretary of Energy to "provide for the effective management" of U.S. nuclear weapons, including the extension of the service life of those weapons.
The program has five objectives: 1) to increase "the reliability, safety, and security" of U.S. nuclear weapons, 2) to further reduce the likelihood of nuclear testing, 3) to achieve reductions in the future size of the stockpile, 4) to reduce the risk of an accidental detonation of a U.S. nuclear weapon, and 5) to prevent unauthorized use of such a weapon. The legislation requires that any changes to the stockpile conform to those objectives, and further, that any changes "remain consistent with basic design parameters by including, to the maximum extent feasible, components that are well understood or are certifiable without the need to resume underground nuclear weapons testing." Any changes must also "use the design, certification, and production expertise resident in the nuclear complex to fulfill current mission requirements of the existing stockpile."
The stockpile management program, in other words, would permit the development of a new warhead under various restrictions. The "current mission requirements" clause of the legislation suggests that any new design should not introduce new military capabilities. Furthermore, the legislation requires that any new design adhere to well known designs and components, and be undertaken only in support of further reductions in the stockpile and the continued moratorium on nuclear tests. The program does not require a new warhead, and instead enables the NNSA to continue modernizing the U.S. nuclear stockpile along a spectrum of options ranging from monitoring and refurbishment to the manufacture of "new" weapons.
Undersecretary of State for Arms Control and International Security Ellen Tauscher told reporters that under the stockpile management program, new features could be added to existing warheads to make them theft-proof and more environmentally friendly (pre-detonation, that is), as long as they are not improved militarily. In her former role as chair of the Strategic Forces Subcommittee of the House Armed Services Committee, Tauscher was instrumental in ending the RRW program and drafting the language on stockpile management.
President Obama declared the United States' commitment to a world without nuclear weapons in his April 5 speech in Prague. Obama also stated that, so long as nuclear weapons exist, the United States would maintain a "safe, secure and effective" nuclear arsenal. The presidential budget request for fiscal year 2011, released on February 1, 2010, calls for substantial investments in the nuclear weapons complex and weapons stockpile, in keeping with the latter principle. For "directed stockpile work," which includes life extension programs, stockpile monitoring and maintenance, and weapons dismantlement, the administration has requested $1.9 billion, an increase of 26 percent from the previous year's appropriation.
The most substantial boost in requested funding goes to the B61 bomb. In fiscal year 2010, Congress appropriated $92 million for sustainment of the B61 and a study of its non-nuclear components. At the time, Congress declined to appropriate an additional $32.5 million to study the nuclear components of the B61. For FY 2011, the administration is requesting $317 million. The bulk of the increase is meant to fund a life extension study of both the nuclear and non-nuclear components of the B61. The report will consider:
"concepts and costs to replace arming and fuzing components…to address near term end-of-life and sustainment concerns on the B61 bomb family. The study will evaluate options for improving safety and use control features and ensures compatibility and integration with modern aircraft such as the F-35 Joint Strike Fighter."
Sustainment programs for all other warhead families would also receive smaller increases in funding under the request, with the exception of the W88. All told, the administration requested $649.4 million sustainment programs for all warhead families, an 81% increase over the previous year's appropriation of $357.8 million.
The NNSA is currently pursuing one LEP, for the W76 warhead. The budget request asks for $249.5 million for that program, a 12 percent increase from the $223.2 million appropriated in fiscal year 2010. The increase is meant to allow NNSA to "scale up to full production" of refurbished warheads by fiscal year 2013.
In sum, the entire NNSA budget request for weapons activities is more than $7 billion. According to the budget justification submitted to Congress:
"Increased funding is requested for programs in direct support of the nuclear weapons stockpile, for scientific, technical and engineering activities related to maintenance assessment and certification capabilities for the stockpile, and for critical infrastructure improvements. The stockpile management program is funded within this appropriation."
The United States continues to monitor and modernize its nuclear weapons and delivery vehicles through the Stockpile Stewardship Program and Life Extension Programs. An independent panel of scientists has found that this strategy can ensure the reliability of the U.S. nuclear deterrent for many years. Others, including 41 U.S. senators, argue that a new warhead is essential to a credible deterrent. The current stockpile management program allows for the design and manufacture of new warheads, alongside the Stockpile Stewardship Program, although only under certain conditions and with specific objectives. President Obama's proposed budget for fiscal year 2011 requests significantly higher expenditures on stockpile maintenance, at a time of strained budgetary resources.
Nonetheless, production of new warheads, even within the strictures established by the stockpile management program, could entail significant political risks to the United States' nonproliferation agenda by conveying a renewed commitment to nuclear arms.
Ultimately, policymakers must weigh the practical costs and benefits of various modernization options against the political costs and benefits of those options. An expanded effort to modernize U.S. nuclear weapons could help win Senate consent for a new arms control agreement with Russia and/or for the ratification of the CTBT. The ratification of such agreements by the United States could offset the political damage caused in the international community as a result of any modernization program, particularly if that program had a limited and clearly-defined scope. However, proponents should not lose sight of the importance of stricter international nonproliferation measures like the IAEA additional protocol, and the difficulty of persuading states to adopt such measures if other countries remain concerned about the depth of the U.S. commitment to nuclear disarmament.
 "Remarks by President Barack Obama," Hradcany Square, Prague, Czech Republic. April 5, 2009, www.whitehouse.gov.
 "Next US president should modernise nuclear arsenal," Senator John Kyl, Financial Times, July 1, 2008, www.ft.com.
 Letter to President Barack Obama, Mitch McConnell et al, December 15, 2009.
 "U.S. Nuclear Stockpile," Office of the Deputy Assistant to the Secretary of Defense for Nuclear Matters, www.acq.osd.mil.
 "Some Little-Publicized Difficulties with a Nuclear Freeze," Dr. J.W. Rosengren, R&D Associates, under Contract to the Office of International Security Affairs, U.S. Department of Energy, October 1983, pp. 5-6; reprinted in U.S. Congress. Senate. Committee on Foreign Relations. Nuclear Testing Issues. 99th Cong., 2nd sess., Senate Hearing 99-937, 1986, pp. 167-68. Quoted in "The Reliable Replacement Warhead Program: Background and Current Developments," Jonathan Medalia, Congressional Research Service. July 27, 2009.
 R.E. Kidder, "Maintaining the U.S. Stockpile of Nuclear Weapons During a Low-Threshold or Comprehensive Test Ban," Lawrence Livermore National Laboratory, University of California, October 1987.
 Sidney Drell, Raymond Jeanloz, et al., Remanufacture, MITRE Corporation, JASON Program Office, JSR-99-300, October 1999, pp. 4, 8. Quoted in Medalia, July 27, 2009.
 R.J. Hemley et al., "Pit Lifetime," JSR-06-335, MITRE Corp., November 20, 2006, p. 1, www.nukewatch.org.
 "B61 Nuclear Gravity Bomb," Brookings Institution, www.brookings.edu.
 "U.S. Nuclear Stockpile," Office of the Deputy Assistant to the Secretary of Defense for Nuclear Matters, www.acq.osd.mil.
 "The Reliable Replacement Warhead Program: Background and Current Developments," Jonathan Medalia, Congressional Research Service, July 27, 2009, p. 7.
 "Life Extension Programs," National Nuclear Security Administration, https://nnsa.energy.gov.
 Scott Miller, "NNSA Completes B61 Refurbishment," Arms Control Today, March 2009, www.armscontrol.org.
 "U.S. Strategic Nuclear Forces: Background, Developments, and Issues," Amy F. Woolf, Congressional Research Service, July 14, 2009.
 "Nuclear Notebook: U.S. Nuclear Forces, 2009, Robert S. Norris and Hans M. Kristensen, The Bulletin of the Atomic Scientists, March/April 2009.
 "U.S. Strategic Nuclear Forces: Background, Developments, and Issues," Amy F. Woolf, Congressional Research Service, July 14, 2009, p. 12.
 Ibid, p.13.
 Event transcript, "START Follow-On Treaty: Assessing Progress on Nuclear Risk Reduction," Arms Control Association, December 9, 2009, www.armscontrol.org.
 Woolf, "U.S. Strategic Nuclear Forces,", pp. 17, 19.
 "United States Air Force Posture Statement 2009," Department of the Air Force, May 19, 2009. https://www.af.mil.
 "B-52 Stratofortress," U.S. Air Force factsheet, October 2009, www.af.mil.
 "Presentation to the House Armed Services Committee, Subcommittee on Air and Land Forces, United States House of Representatives," Lt. Gen. Daniel J. Darnell et al, May 20, 2009, https://armedservices.house.gov.
 Quoted in Medalia, "The Reliable Replacement Warhead Program: Background and Current Developments,".
 Ibid, p. 2.
 James Sterngold, "Failure to Launch," Mother Jones, January/February 2008, p. 43.
 U.S. House. Committee on Appropriations. Consolidated Appropriations Act, 2008. Explanatory note, www.gpoaccess.gov.
 "America's Strategic Posture," William J. Perry, James R. Schlesinger, et al, Congressional Commission on the Strategic Posture of the United States, 2009, pp. 40-41.
 "Life Extension Program (LEP) Executive Summary, JSR-09-334E, the MITRE Corporation, JASON Program Office, September 9, 2009.
 Robert S. Norris and Hans M. Kristensen, "Nuclear Notebook: U.S. nuclear forces, 2009," Bulletin of the Atomic Scientists, March/April 2009, https://thebulletin.metapress.com.
 "Fiscal 2009 Budget: U.S. Strategic Posture," Statement of Thomas D'Agostino, Committee on House Armed Services Subcommittee on Strategic Forces, CQ Congressional Testimony, February 29, 2008.
 Treaty on the Nonproliferation of Nuclear Weapons, Article V, www.reachingcriticalwill.org.
 Statement by Sweden to the Conference on Disarmament, Ambassador Elisabet Borsiin Bonnier, February 28, 2006, www.reachingcriticalwill.org.
 "Substantive recommendations to the third session of the Preparatory Committee and the 2010 Review Conference," working paper submitted by the Group of Non-Aligned States, May 6, 2009, p. 3.
 "America's Strategic Posture," William J. Perry, James R. Schlesinger, et al, Congressional Commission on the Strategic Posture of the United States, 2009, p. 44.
 National Defense Authorization Act for Fiscal Year 2010, sec. 3113, https://frwebgate.access.gpo.gov.
 "2011 U.S. Budget to Fund Refurbishing of Nukes," William Matthews, Defense News, January 14, 2010, www.defensenews.com.
 "Remarks by President Barack Obama," Hradcany Square, Prague, Czech Republic. April 5, 2009.
 "Department of Energy FY 2011 Congressional Budget Request, National Nuclear Security Administration" page 59, www.cfo.doe.gov.
 Cole Harvey and Daniel Horner, "Congress Funds Nonproliferation Work," Arms Control Today, November 2009, www.armscontrol.org.
 Ibid. page 70.
 Ibid. page 59.
 Ibid. page 59.
 Ibid. page 78.
 Ibid. page 52.
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