Deterrence is emerging as a theme for Secretary of Defense Pete Hegseth, but questions remain about the administration’s ability to deliver and maintain the nation’s nuclear deterrent. At the Air Force Summit on March 19, Hegseth commented on the “sense of urgency” and importance of next-generation airpower as “the decisive factor in whether or not we truly deter our peer [adversaries] of the 21st century.” A week later on March 26, Strategic Command Commander General Anthony Cotton appeared before Congress to speak to the nuclear-specific aspect of that deterrent and emphasized the challenge of sustaining existing nuclear systems while also completing, “the multigenerational, decades-long modernization of all three legs of the nuclear deterrent and its critical [nuclear command, control, and communications] systems.” The military services support nuclear modernization. On March 27, Troy Meink, the nominee for secretary of the Air Force, along with Michael Duffey, the nominee for undersecretary of defense for acquisition and sustainment, both pledged to focus on nuclear modernization, if confirmed, as the “backbone” of the nation’s deterrent as it faces a series of challenges. A month earlier, on February 27, Secretary of the Navy John Phelan addressed concerns about delays in production of the Columbia-class submarine and said, “I think the Columbia submarine program is incredibly important. It is the most important nuclear deterrent we have.” Q1: Why does the United States need to modernize its nuclear arsenal now? A1: One theme from Cotton’s testimony was the need for flexibility—he used the word nine times in reference to the air, land, and sea legs of the nuclear triad. “Flexible response” was one of six fundamental tenets for the United States’ nuclear strategy identified by the 2023 bipartisan Strategic Posture Commission. The commission also concluded that current plans for nuclear modernization were “necessary but not sufficient.” A sense of urgency was palpable in Cotton and others’ testimony about the need not only for modernization, but also for a different nuclear posture and nuclear enterprise than the one we currently have. Efforts to modernize the nuclear triad are long overdue. The newest ICBM in the U.S. force was deployed in 1970 and has undergone repeated life extension programs. Now, more than 40 years after the missile’s originally planned retirement date, the Air Force is considering ways to further extend the service life of Minuteman III because of potential delays with its replacement, Sentinel. The Sentinel program—one of the cornerstones of the current modernization effort—is significantly over budget and triggered a breach of the Nunn-McCurdy Act in 2024. In contrast, the B-21 stealth bomber program (to replace the B-2) is currently on track to finish on time. Other key components of the ongoing modernization effort include the Columbia-class ballistic missile submarine (to replace the Ohio class) and the Long-Range Stand-Off weapon air-launched cruise missile. In addition to these weapons systems, the Department of Defense is working to modernize the nuclear command, control, and communications systems that connect U.S. nuclear forces and decisionmakers. But perhaps the most urgent piece of nuclear modernization is not the platforms and delivery systems, but the enterprise. The U.S. defense industrial base and the U.S. nuclear enterprise are responsible for designing, producing, and maintaining the systems that comprise the U.S. nuclear force, but both atrophied in the years after the Cold War. Former National Security Advisor Jake Sullivan remarked in 2024 that the war in Ukraine exposed how, “decades of underinvestment and consolidation had seriously eroded our defense industrial base. . . . America’s defense industrial base, the one we inherited, was not up to the task that we face in a new age of strategic competition.” Reinvigorating the U.S. defense industrial base generally and the nuclear enterprise specifically will be crucial for modernizing the U.S. nuclear force and maintaining deterrence. Q2: Why is it so expensive? A2: The Congressional Budget Office estimates that the United States will spend $756 billion (approximately $75 billion a year) on its nuclear forces between 2023 and 2032. For comparison, the Manhattan Project cost around $30 billion (in 2023 dollars) in total. There are three reasons for these high costs. First, the United States is attempting to modernize all elements of its nuclear triad simultaneously. In the years following the Cold War, the U.S. nuclear enterprise atrophied due to a lack of funding and attention. Now, in response to the evolving geopolitical landscape, the United States is attempting to recapitalize the entire enterprise at once. In addition to developing new weapons systems—ranging from stealth bombers to nuclear warheads—this entails revitalizing the infrastructure to produce, maintain, and operate the nuclear triad, while also continuing to maintain and operate Cold War–era systems. Second, certain modernization programs have faced cost overruns as a result of poor planning and faulty assumptions. The Sentinel intercontinental ballistic missile (ICBM), for example, is projected to cost 81 percent more than initial estimates because some projections failed to fully account for the costs of updating the supporting ground infrastructure, including missile silos and communications wiring. The Columbia submarine program is also likely to face cost overruns and delays due to a range of supply chain and workforce-related challenges. Third, military equipment has generally become more expensive. Between 1950 and 2000, the price of U.S. attack submarines, amphibious ships, and surface ships grew by an average of 10 percent annually—double the rate of inflation. This trend reflects the growing complexity of military systems: While today’s nuclear delivery systems are more expensive than their Cold War counterparts, they are also far more capable. Although current spending on nuclear forces dwarfs that of historical efforts, it is actually relatively cheap by Department of Defense standards. In FY 2024, spending on the U.S. nuclear force amounted to around 7 percent of the defense budget, depending on calculation methods. Given the vital role that the nuclear force plays in supporting U.S. national security, Congress should continue to fund all aspects of modernization to ensure that the United States can build a deterrent fit for the current threat landscape. Q3: What is the status of adversaries’ nuclear modernization A3: The United States’ principal nuclear adversaries have made significant progress in modernizing and expanding their nuclear forces. Russia is in the final stages of a decades-long effort to modernize its Cold War–era arsenal. Russia currently operates a force of modernized bombers, new ICBMs, ballistic missile submarines (SSBNs), and a wide variety of modern theater delivery systems. As of 2023, Former Russian Defense Minister Sergei Shoigu reported that modern weaponry comprised 95 percent of Russia’s nuclear triad. China, on the other hand, is in the process of rapidly expanding and modernizing its strategic force. The Department of Defense assesses that China currently possesses over 600 operational nuclear warheads and will likely possess over 1,000 by 2030. Like Russia, China operates a wide range of regional and strategic delivery systems, and General Cotton’s testimony confirmed that China has now deployed six nuclear-armed Jin-class SSBNs. The diversity of Russian and Chinese nuclear forces—in terms of delivery systems and warhead yield—provides them with flexibility in the event of a crisis and confers coercive bargaining advantages against the United States, which lacks a similarly diverse arsenal. This flexibility is concerning, particularly given the growing risk of a conflict with China in the Pacific, and U.S. adversaries’ ambiguous nuclear doctrines that create uncertainty about the threshold for nuclear use. Q4: Can allies do more? A4: Yes and no. In his testimony, Cotton referred to allies as the United States’ “asymmetric advantage.” European allies contribute to the NATO nuclear mission by buying and flying F-35s, providing conventional support to nuclear operations as part of conventional-nuclear integration, and the United Kingdom and France have their own nuclear deterrents, although France remains outside the NATO Nuclear Planning Group. This allied support will be critical for a more flexible U.S. nuclear force, given its contributions at the regional level. None of the United States’ allies in the Indo-Pacific have nuclear weapons. Asking allies to do more conventionally could enhance deterrence against key adversaries. But there are still nuclear functions only the United States can (and should) provide. The United Kingdom maintains a credible minimum nuclear deterrent on a single sea-based leg, and France has air- and sea-delivered platforms. While there are nuclear functions only the United States can provide to deter Russia, which is armed with over 4,380 warheads, including 1,558 tactical nuclear weapons, if London and Paris could do more to provide the alliance with nuclear sub-strategic options, it would also contribute to a more flexible deterrent. An end to the war in Ukraine does not appear likely to spell the end for Russia’s regional ambitions. Rather than considering European-led options for regional deterrence, therefore, the United States needs to work with allies to explore how to enhance conventional-nuclear integration and establish a deterrence division of labor. Q5: Why are “flexible” forces so important? A5: In the 1960s, President Kennedy changed the United States’ nuclear posture to one of “flexible response” because a wider range of nuclear response options was seen as more credible than escalation to “massive retaliation.” The shift was largely driven by the need to reassure U.S. allies in Europe. But “flexible response” for the twenty-first century is primarily being driven by U.S. adversaries. Russia and China have been quantitatively and qualitatively expanding their arsenals to support regional ambitions. The 2025 Annual Threat Assessment of the Intelligence Community, for example, found that “Russia’s growing confidence in its battlefield superiority and defense industrial base and increased risk of nuclear war, create both urgency and complications for U.S. efforts to bring the war (in Ukraine) to an acceptable close.” With regards to China, the Posture Commission, along with numerous other government and nongovernmental studies, identified the challenges of China’s rapid nuclear buildup, questions about the seriousness of its no-first-use policy, and ambitions for Taiwan as challenges for the U.S. strategic posture. The result is a strategic landscape that is more complex, with more actors, and new risks such as simultaneous conflict in two theaters. A more flexible nuclear force will afford the president more nuclear options in the event of a crisis, enhancing the credibility of the United States’ deterrent. It will also impact adversaries’ perceptions, both by signaling U.S. resolve to regional deterrence and by creating uncertainty in adversary capitals about U.S. escalation management, which could also have a deterrent effect. As part of its ongoing study series, Project Atom, CSIS’s Project on Nuclear Issues has used a competitive strategies approach to answer big strategic questions, such as how to deter two peer competitors and how to strengthen intra-war deterrence in the event of crisis escalation and deterrence failure. One of the enduring findings of the competitive strategies has been the need for flexibility in the United States’ nuclear force posture. For example, Project Atom 2023 concluded, “The United States needs more flexibility and agility in its arsenal, whether that be with more advanced conventional capabilities, additional new nuclear delivery platforms, or the ability to adjust modernization plans.” And the 2024 study recommended, “U.S. policymakers should strive to diversify U.S. nuclear forces through investments in new regional capabilities so that the president will have a broader range of credible options, particularly if an adversary threatens limited nuclear attacks.” In practice, a more flexible force will require at least three main components. First and foremost are more regional nuclear capabilities, such as SLCM-N or a stand-off capability, along with non-nuclear enabling and strike capabilities, including a larger fleet of aerial refueling tankers. Second, building a more flexible force will require greater investment in the National Nuclear Security Administration (NNSA) and the National Labs, with a special focus on increasing the capacity for lithium and tritium production. General Cotton referred to the National Labs as a “force multiplier” for the U.S. nuclear force. Funding for NNSA and the labs—currently a small fraction of government spending—should reflect the importance of that role. Third and finally, a more flexible nuclear force will require renewed investments in the defense industrial base. Rebuilding the nuclear workforce needed to design and produce advanced nuclear systems will be vital for ensuring the success of U.S. modernization and the ability of the enterprise to meet future challenges. Heather Williams is director of the Project on Nuclear Issues and senior fellow with the Defense and Security Department at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Lachlan MacKenzie is a research associate with the Project on Nuclear Issues in the Defense and Security Department at CSIS. Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s). © 2025 by the Center for Strategic and International Studies. All rights reserved.