Nuclear Notebook: United States nuclear weapons, 2021

By Hans M. Kristensen, Matt Korda

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At the beginning of 2021, the US Defense Department maintained an estimated stockpile of 3,800 nuclear warheads for delivery by 800 ballistic missiles and aircraft. Most of the warheads in the stockpile are not deployed, but rather stored for potential upload onto missiles and aircraft as necessary. Many are destined for retirement. We estimate that approximately 1,800 warheads are currently deployed, of which roughly 1,400 strategic warheads are deployed on ballistic missiles and another 300 at strategic bomber bases in the United States. An additional 100 tactical bombs are deployed at air bases in Europe. The remaining warheads—approximately 2,000—are in storage as a so-called hedge against technical or geopolitical surprises. Several hundred of those warheads are scheduled to be retired before 2030. (See Table 1.)

Table 1: US nuclear forces, 2021

In addition to the warheads in the Defense Department stockpile, approximately 1,750 retired— but still intact—warheads are stored under custody of the Energy Department and are awaiting dismantlement, giving a total US inventory of an estimated 5,550 warheads. Between 2010 and 2018, the US government publicly disclosed the size of the nuclear weapons stockpile. But in 2019, the Trump administration rejected a request from the Federation of American Scientists to declassify the latest stockpile number, and these numbers remain classified at the time of this publication (Aftergood 2019; Kristensen 2019a).

The nuclear weapons are thought to be stored at an estimated 24 geographical locations in 11 US states and five European countries. The location with the most nuclear weapons by far is the large Kirtland Underground Munitions and Maintenance Storage Complex south of Albuquerque, New Mexico. Most of the weapons in this location are retired weapons awaiting dismantlement at the Pantex Plant in Texas. The state with the second-largest inventory is Washington, which is home to the Strategic Weapons Facility Pacific and the ballistic missile submarines at Naval Submarine Base Kitsap. (Washington is the state with most nuclear weapons if counting only stockpiled weapons).

Implementing New START

The United States appears to be in compliance with the New START treaty limits, with 675 deployed strategic launchers with 1,457 attributed warheads counted as of October 1, 2020, well below the limits of 700 deployed strategic launchers with 1,550 warheads. Another 125 launchers were not deployed, for a total inventory of 800 deployed and non-deployed launchers (State Department 2020a). This is an increase of 20 deployed strategic launchers and 85 deployed strategic warheads over the past 6 months (State Department 2020b). However, these are not actual increases; they reflect normal fluctuations caused by launchers moving in and out of maintenance. The United States has not reduced its total inventory of strategic launchers since 2017 (Kristensen 2020a).

The numbers reported by the State Department differ from the estimates presented in this Nuclear Notebook because the New START counting rules artificially attribute one warhead to each deployed bomber, even though US bombers do not carry nuclear weapons under normal circumstances, and because this Nuclear Notebook counts weapons stored at bomber bases that can quickly be loaded onto the aircraft.

Since the treaty entered into force in February 2011, the biannual aggregate data show the United States has cut a total of 324 strategic launchers, 207 deployed launchers, and 343 deployed strategic warheads from its inventory. The warhead reduction represents approximately 9 percent of the of the 3,800 warheads remaining in the US stockpile, and approximately 6 percent of the total US arsenal of 5,550 stockpiled and retired warheads awaiting dismantlement.

The 2018 Nuclear Posture Review states that the United States “will continue to implement the New START Treaty” while it remains in effect (Department of Defense 2018, 73). The treaty will remain in effect until February 2021, at which point it may be extended for up to five years (either a single, five-year extension, or multiple extensions adding up to five years) with mutual agreement. Although it is unlikely to withdraw from New START entirely, the Trump administration appears to have little interest in a clean extension of the treaty. After waiting more than three years to begin bilateral arms control talks in earnest, the Trump administration has recently walked its position back from an initial prerequisite on including China to a willingness to agree to an unverifiable bilateral warhead freeze. This is equal parts shocking and confusing, given that the Trump administration spent its entire four-year term in office criticizing New START for being a “bad deal”––specifically because of its presumed verification deficiencies and a lack of Chinese participation (Gertz 2020).

The United States is currently 25 launchers and 93 warheads below the treaty limit for deployed strategic weapons, but has 165 deployed launchers more than Russia––a significant gap that exceeds the size of an entire US Air Force ICBM wing. It is notable that Russia has not sought to reduce this gap by deploying more strategic launchers. Instead, the Russian launcher deficit has increased by one-third since its lowest point in February 2018.

If New START were allowed to expire, both Russia and the United States could upload several hundreds of extra warheads onto their launchers, which means that the treaty has proven useful thus far in keeping a lid on both countries’ nuclear modernization plans. Additionally, if New START expired, then both countries would lose a critical node of transparency into each other’s nuclear forces. As of October 29, 2020, the United States and Russia have completed a combined 328 on-site inspections and exchanged 21,038 notifications (State Department 2020c). Only two inspections each have been conducted by the United States and Russia during this treaty year, because inspections were paused due to the COVID-19 pandemic.

The Nuclear Posture Review and nuclear modernization

Although the Trump administration’s 2018 Nuclear Posture Review (NPR) followed the broad outlines of the Obama administration’s 2010 NPR to modernize the entire nuclear weapons arsenal, it includes several important changes.

The most significant change is a recommendation to increase the types and role of US nuclear weapons. The Trump NPR takes a confrontational tone, presenting an assertive posture that embraces “Great Power competition,” and includes plans to develop new nuclear weapons and modify others. The report backs away from the goal of seeking to limit the role of nuclear weapons to the sole purpose of deterring nuclear attacks, and instead emphasizes “expanding” US nuclear options to deter, and, if deterrence fails, to prevail against both nuclear and “non-nuclear strategic attacks.” To be clear, any use of a nuclear weapon to respond to a non-nuclear strategic attack would constitute nuclear first use.

The NPR explains that “non-nuclear strategic attacks include, but are not limited to, attacks on the U.S., allied, or partner civilian population or infrastructure, and attacks on U.S. or allied nuclear forces, their command and control, or warning and attack assessment capabilities” (Department of Defense 2018, 21). US nuclear capabilities will be postured to “hedge against the potential rapid growth or emergence of nuclear and non-nuclear strategic threats, including chemical, biological, cyber, and large-scale conventional aggression” (Department of Defense 2018, 38). To achieve these goals, the NPR states that “the United States will enhance the flexibility and range of its tailored deterrence options. … Expanding flexible US nuclear options now, to include low-yield options, is important for the preservation of credible deterrence against regional aggression,” the report claims (Department of Defense 2018, 34).

The new tailored capabilities include modifying “a small number” of the existing W76-1 90-kiloton two-stage thermonuclear warheads to single-stage warheads by “turning off” the secondary to limit the yield to what the primary can produce (an estimated 5–7 kilotons). This new warhead (W76-2), the NPR claims, is necessary to “help counter any mistaken perception of an exploitable ‘gap’ in US regional deterrence capabilities.” Undersecretary of Defense for Policy John Rood told reporters in December 2019 that the low-yield Trident warhead was “very stabilizing” and in no way supported the concept of early use of low-yield nuclear weapons (Kreisher 2019), even though the NPR explicitly states the weapon is being acquired to provide “a prompt response option” (Department of Defense 2018).

In the longer term, the NPR declares that the United States will also “pursue a nuclear-armed” submarine-launched cruise missile to “provide a needed nonstrategic regional presence, an assured response capability, and an INF-Treaty compliant response to Russia’s continuing Treaty violation.” The NPR specifically notes that, “If Russia returns to compliance with its arms control obligations, reduces its non-strategic nuclear arsenal, and corrects its other destabilizing behaviors, the United States may reconsider the pursuit of a [submarine-launched cruise missile].” In pursuit of this new missile, the review states “we will immediately begin efforts to restore this capability by initiating a requirements study leading to an Analysis of Alternatives … for the rapid development of a modern [submarine-launched cruise missile].” The report’s authors believe that “US pursuit of a submarine-launched cruise missile may provide the necessary incentive for Russia to negotiate seriously a reduction of its nonstrategic nuclear weapons, just as the prior Western deployment of intermediate-range nuclear forces in Europe led to the 1987 INF Treaty” (Department of Defense 2018, 55).

The new nuclear “supplements” proposed by the NPR are needed, the authors say, to “provide a more diverse set of characteristics greatly enhancing our ability to tailor deterrence and assurance; expand the range of credible US options for responding to nuclear or non-nuclear strategic attack; and, enhance deterrence by signaling to potential adversaries that their concepts of coercive, limited nuclear escalation offer no exploitable advantage” (Department of Defense 2018, 55).

Yet the US arsenal already includes around 1,000 gravity bombs and air-launched cruise missiles with low-yield warhead options (Kristensen 2017a). The NPR provides no evidence that existing capabilities are insufficient or document that the yield of US nuclear weapons is a factor in whether Russia would decide to use nuclear weapons. The NPR authors simply claim that the new capabilities are needed. The US Navy used to have a nuclear submarine-launched cruise missile (the TLAM/N) but retired it in 2011 because it was redundant and no longer needed. All other nonstrategic nuclear weapons—with the exception of gravity bombs for fighter-bombers—have also been retired because there was no longer any military need for them, despite Russia’s larger nonstrategic nuclear weapons arsenal.

The suggestion that a US submarine-launched cruise missile (SLCM) could motivate Russia to return to compliance with the Intermediate-Range Nuclear Forces (INF) Treaty is flawed because Russia embarked upon its current violation of the treaty at a time when the TLAM/N was still in the US arsenal, and because the Trump administration has since withdrawn the United States from the INF Treaty. Moreover, US Strategic Command has already strengthened strategic bombers’ support of NATO in response to Russia’s more provocative and aggressive behavior (see above); 46 B-52 bombers are currently equipped with the air-launched cruise missile (ALCM) and both the B-52 and the new B-21 bomber will receive the new long-range standoff (LRSO) weapon, which will have essentially the same capabilities as the SLCM proposed in the NPR.

Russia’s decisions about the size and composition of its nonstrategic arsenal appear to be driven by the US military’s superiority in conventional forces, not by the US nonstrategic nuclear arsenal or by the yield of a particular weapon. Instead, the pursuit of a new nuclear SLCM to “provide a needed nonstrategic regional presence” in Europe and Asia could increase Russia’s reliance on nonstrategic nuclear weapons and could potentially even trigger Chinese interest in such a capability as well—especially when combined with the parallel expansion of US long-range conventional strike capabilities including development of new conventional INF-range missiles.

One final argument against the SLCM is that nuclear-capable vessels triggered frequent and serious political disputes during the Cold War when they visited foreign ports in countries that did not allow nuclear weapons on their territory. In the case of New Zealand, diplomatic relations have only recently—30 years later—recovered from those disputes. Reconstitution of a nuclear SLCM would reintroduce this foreign relations irritant and needlessly complicate relations with key allied countries in Europe and Northeast Asia

According to an estimate published in January 2019 by the US Congressional Budget Office (CBO), modernizing and operating the US nuclear arsenal and the facilities that support it will cost around $494 billion for the period 2019–2028 (Congressional Budget Office 2019, 1). This is $94 billion more than CBO’s 2017 estimate for the 2017–2026 period, in part because modernization programs continue to ramp up, cost estimates are increasing, and because of the NPR’s call for new nuclear weapons. The nuclear modernization (and maintenance) program will continue well beyond 2028 and, based on the CBO’s estimate, will cost $1.2 trillion over the next three decades. Notably, although the CBO estimate accounts for inflation (Congressional Budget Office 2017), other estimates forecast that the total cost will be closer to $1.7 trillion (Arms Control Association 2017). Whatever the actual price tag will be, it is likely to increase over time, resulting in increased competition with conventional modernization programs planned for the same period. The NPR belittles concerns about affordability issues in the nuclear modernization program and instead labels it “an affordable priority,” pointing out that the total cost is only a small portion of the overall defense budget (Department of Defense 2018, XI). There is little doubt, however, that limited resources, competing nuclear and conventional modernization programs, tax cuts, and the rapidly growing US budget deficit will present significant challenges for the nuclear modernization program.

Nuclear planning, nuclear exercises

The changes in the Trump administration’s Nuclear Posture Review so far do not appear to have required new guidance from the White House on nuclear weapons strategy. The previous guidance, issued in 2013, also reaffirmed the importance of nuclear weapons and modernization and emphasized a strong counterforce strategy—planning principles that have already been incorporated into a host of highly flexible strategic and regional nuclear strike plans (Kristensen 2013a).

This includes a “family” of plans organized under the strategic “Operations Plan (OPLAN) 8010–12,” and also into various regional plans. The OPLAN, which is named “Strategic Deterrence and Force Employment” and first entered into effect in July 2012 in response to Operations Order (OPORD) Global Citadel signed by the secretary of defense, is flexible enough to absorb normal changes to the posture as they emerge, including those flowing from the NPR. Several updates have been published since 2012. OPLAN 8010–12 is part of a broader plan that also includes conventional weapons such as the Tactical Tomahawk submarine-launched cruise missile and the extended-range Joint Air-to-Surface Standoff Missile, as well as missile defense and cyber. OPLAN 8010–12 includes strike options against Russia, China, North Korea, and Iran. Although the Trump administration’s NPR criticizes Russia for an alleged willingness to use nuclear weapons first as part of a so-called escalate-to-deescalate strategy, OPLAN 8010–12 also “emphasizes escalation control designed to end hostilities and resolve the conflict at the lowest practicable level” by developing “readily executable and adaptively planned response options to de-escalate, defend against, or defeat hostile adversary actions” (US Strategic Command 2012). This objective is not just directed at nuclear attacks, as the 2018 NPR calls for “expanding” US nuclear options against “non-nuclear strategic attacks.”

The strategic war plan is a whole-of-government plan that includes the full spectrum of national power to affect potential adversaries. This integration of nuclear and conventional kinetic and non-kinetic strategic capabilities into one overall plan is a significant change from the strategic war plan of the Cold War, which was almost entirely nuclear. Former US Strategic Command (STRATCOM) commander Gen. John Hyten, now the Chairman of the Joint Chiefs of Staff, in 2017 explained the scope of modern strategic planning:

I’ll just say that the plans that we have right now, one of the things that surprised me most when I took command on November 3 was the flexible options that are in all the plans today. So we actually have very flexible options in our plans. So if something bad happens in the world and there’s a response and I’m on the phone with the secretary of defense and the president and the entire staff, which is the attorney general, secretary of state, and everybody, I actually have a series of very flexible options from conventional all the way up to large-scale nuke that I can advise the president on to give him options on what he would want to do.

So I’m very comfortable today with the flexibility of our response options. Whether the president of the United States and his team believes that that gives him enough flexibility is his call. So we’ll look at that in the Nuclear Posture Review. But I’ve said publicly in the past that our plans now are very flexible.

And the reason I was surprised when I got to [Strategic Command] about the flexibility, is because the last time I executed or was involved in the execution of the nuclear plan was about 20 years ago, and there was no flexibility in the plan. It was big, it was huge, it was massively destructive, and that’s all there. We now have conventional responses all the way up to the nuclear responses, and I think that’s a very healthy thing (Hyten 2017).

To practice and fine-tune these plans, the armed forces conducted several nuclear-related exercises in 2020. These included STRATCOM’s Global Lightning exercise in January, a command and control and battle staff exercise designed to assess joint operational readiness across all of STRATCOM’s mission areas. To that end, Global Lightning is typically a globally integrated exercise that links to several other exercises. In 2019, Global Lightning was designed to support US European Command (USEUCOM) and was thus linked to several Europe-focused exercises including USEUCOM’s Exercise Austere Challenge and the United Kingdom’s Exercise Joint Venture (US Strategic Command 2019a). In 2019, at the start of Global Lightning, four B-52s deployed to Royal Air Force Fairford in England (two more joined later) for month-long operations over Europe, which included unprecedented four-bomber strike formations over the eastern Baltic Sea (US Air Forces In Europe 2019a) and north along the Norwegian coast (US Air Forces In Europe 2019b).

In 2020, the exercise was linked to US Cyber Command’s Exercise Cyber Lightning 2020, North American Aerospace Defense Command and US Northern Command’s Exercise Vigilant Shield 2020, US Transportation Command’s Exercise Turbo Challenge, and a US Space Command exercise (US Strategic Command 2020a).

Notably, the 2020 Global Lightning exercise was the first to be conducted entirely from STRATCOM’s new Command and Control Facility, also known as C2F. Dedicated to General Curtis E. LeMay, the new facility includes over 650 miles of telecommunications cables––“enough to link Omaha to Dallas”––and will function as “the heart of the nation’s nuclear command” (US Strategic Command 2019b).

In October 2020, STRATCOM conducted its annual week-long Global Thunder exercise. The exercise, which involved more than 150,000 personnel, focused on “providing realistic training on joint operations and nuclear readiness” (US Strategic Command 2020b). The exercise also included significant non-nuclear or mixed components, such as practice loadings of the conventional Joint Air-to-Surface Standoff Missile and BLU-109 conventional bunker busters in conjunction with B61-7 strategic nuclear gravity bombs (Kristensen 2020c).

Just like the 2019 exercise, Global Thunder coincided with the participation of US strategic bombers in European deterrence exercises. In 2019, the United States conducted several B-52 missions very close to Russian airspace, including a likely simulated bombing strike against Russian forces in Kaliningrad, and another unprecedented three-aircraft B-52 formation flying deep into the Barents Sea––only about 300 kilometers (200 miles) from Russia’s naval base on the Kola Peninsula. In 2020, two B-52s from the 2nd Bomb Wing at Barksdale Air Force Base participated in a two-week NATO Bomber Task Force exercise, following an earlier exercise in August called Allied Sky, wherein six B-52s flew over all 30 NATO countries in a single day (US European Command 2020; NATO 2020a). In June, B-52s from Minot Air Force Base also conducted flights over the Arctic Ocean and participated in the Baltic Sea operation BALTOPS (US Air Forces in Europe 2020; US Strategic Command 2020c).The US Air Force has increased bomber operations as part of a Great Power Competition strategy, with frequent flights over all areas around Russia. This image shows US B-52 bomber and Norwegian F-16 fighters over Northern Norway in November 2019 before the bombers continued into the Barents Sea near Russia’s strategic submarine base on the Kola Peninsula. (Image: US Air Force).

These operations mark a peak in steadily increasing US bomber operations in Europe since Russia’s invasion of Ukraine in 2014. Before that, one or two bombers would deploy for an exercise or airshow. But since then, the number of deployments and bombers has increased, and the mission changed. Very quickly after the Russian annexation of Crimea, STRATCOM increased the role of nuclear bombers in support of EUCOM (Breedlove 2015), which in 2016 put into effect a new standing war plan for the first time since the Cold War (Scapparotti 2017). Before 2018, the bomber mission was called the Bomber Assurance and Deterrence missions to show the flag, but now the bombers deploy as a Bomber Task Force that brings the full offensive capability to the forward base. Whereas the mission of Bomber Assurance and Deterrence was to train with allies and have a visible presence to deter Russia, the mission of the Bomber Task Force is to move a fully combat ready bomber force into the European theater. “It’s no longer just to go partner with our NATO allies, or to go over and have a visible presence of American air power,” according to the commander of the 2nd Bomb Wing. “That’s part of it, but we are also there to drop weapons if called to do so” (Wrightsman 2019).

These changes are important indications of how US strategy has changed in response to deteriorating East-West relations and the new “Great Power competition” strategy promoted by the Trump administration. They also illustrate a growing integration of nuclear and conventional capabilities that is frequently overlooked. The deployment of four B-52s to Royal Air Force Fairford in March 2019, for example, included two nuclear-capable aircraft and two that have been converted to conventional-only missions. NATO’s official announcement of the exercise did not notice this feature but said the deployment “shows that the US nuclear umbrella protects Europe.” (NATO 2019). The statement also said that the B-52 bombers “can carry both conventional and nuclear weapons” when, in fact, nearly half of them—41 of 87—cannot because they have been denuclearized under the New START treaty. The close integration of nuclear and conventional bombers into the same task force can have significant implications for crisis stability, misunderstandings, and the risk of nuclear escalation.

Land-based ballistic missiles

The US Air Force operates a force of 400 silo-based Minuteman III ICBMs split across three wings: the 90th Missile Wing at F. E. Warren Air Force Base in Colorado, Nebraska, and Wyoming; the 91st Missile Wing at Minot Air Force Base in North Dakota; and the 341st Missile Wing at Malmstrom Air Force Base in Montana. In addition to the 400 silos with missiles, another 50 silos are kept “warm” to load stored missiles if necessary. Each wing has three squadrons, each with 50 Minuteman III silos. They are collectively controlled by five launch control centers.

The 400 ICBMs as deployed carry one warhead each, either a 300-kiloton W87/Mk21 or a 335-kiloton W78/Mk12A. ICBMs equipped with the W78/Mk12A, however, could theoretically be uploaded to carry two or three independently targetable warheads each, for a total of 800 warheads available for the ICBM force. The ICBMs completed a multibillion-dollar, decade-long modernization program in 2015 to extend the service life of the Minuteman III to 2030. Although the United States did not officially deploy a new ICBM, the upgraded Minuteman IIIs “are basically new missiles except for the shell,” according to Air Force personnel (Pampe 2012).

An ongoing Air Force modernization program involves upgrades to the arming, fuzing, and firing component of the Mk21 reentry vehicle, at a cost of slightly over a billion dollars in total. The publicly stated purpose of this refurbishment is to extend the vehicles’ service life, but the effort appears to also involve adding a “burst height compensation” to enhance the targeting effectiveness of the warheads (Postol 2014). Priority is on replacement of the Mk21 fuze. A total of 693 fuze replacements were initially planned; however, the new fuzes will also reportedly be deployed on the Minuteman replacement missile, which means that the fuze modernization program is likely to expand significantly to accommodate those new missiles (Woolf 2020, 15-16). The effort complements a similar fuze upgrade underway to the Navy’s W76-1/Mk4A warhead. The enhanced targeting capability might also allow for lowering the yield on future warhead designs.

It is possible to do a second life-extension of the Minuteman III. In March 2019, the Air Force’s Deputy Chief of Staff for Strategic Deterrence and Nuclear Integration noted in his testimony to the House Subcommittee on Strategic Forces that there was one more opportunity to life-extend the missiles before the Minuteman III would have to be replaced (Clark 2019). However, the Air Force has decided against life-extension, instead opting to purchase a whole new generation of ICBMs.

In August 2017, the Air Force awarded $678 million worth of contracts to Boeing and Northrop Grumman to develop trade studies for the next-generation ICBM that is currently known as the Ground-Based Strategic Deterrent (GBSD) (Erwin 2018). In October 2019, the Program Manager for GBSD noted that the official name for the missile would be selected within 12 months; however, over a year later an official name has still not yet been announced (Bartolomei 2019). On July 16, 2019, the Air Force issued a formal “request for proposals” for the Engineering and Manufacturing Development (EMD) phase of the GBSD program, which includes five production lot options to produce and deploy the system (Bryant 2019).

As the two companies under contract for the GBSD’s Technology Maturation and Risk Reduction phase, Boeing and Northrop Grumman were both expected to bid for the EMD contract. However, only a week after the request for proposals was issued, Boeing surprisingly walked away from the competition, stating that “the current acquisition approach does not provide a level playing field for fair competition” (Weisgerber 2019). The dispute centers on Northrop Grumman’s 2018 acquisition of Orbital ATK, which is one of only two US-based companies that produces solid rocket motors and launch vehicles. Under the terms of the acquisition, Northrop Grumman is required to provide “for solid rocket motors to be available on a non-discriminatory basis under certain conditions and processes.” However, Boeing has expressed concern that Northrop Grumman would not comply with that order, thus putting Northrup Grumman at a favorable position in the bidding process over Boeing, which does not produce those systems in-house. Despite Boeing’s stated intention to not submit a bid for the EMD contract, Boeing conducted a substantial lobbying campaign throughout the summer of 2019, in an effort to convince Congress and the Air Force to force Northrop Grumman into submitting a joint “best-of-industry” bid with Boeing (Mehta 2019). However, Northrop Grumman declined Boeing’s offer and the Air Force did not intervene to force a joint bid. The Air Force subsequently terminated the remainder of Boeing’s Technological Maturation and Risk Reduction contract in October 2019 by refusing to allocate any further funding to the contract, thus effectively ending Boeing’s involvement with the GBSD program (Insinna 2019).

By December 13, 2019––the Request for Proposal deadline for the EMD contract––the Air Force received only a single bid for the contract, and on September 8, 2020, the Air Force officially awarded the $13.3 billion EMD contract to Northrop Grumman. The nationwide team will include Aerojet Rocketdyne––which will produce the system’s solid-fuel rocket motors in conjunction with newly-acquired Orbital ATK, which is now called Northrop Grumman Innovation Systems––General Dynamics, Collins Aerospace, Lockheed Martin, Textron Systems, HDT Global, Bechtel, Kratos Defense and Security Solutions, Clark Construction, L3Harris, and Honeywell (Northrop Grumman 2020).

According to the Air Force’s latest milestone requirements, the Air Force must deploy 20 new GBSD missiles with legacy reentry vehicles and warheads in order to achieve Initial Operating Capability, which is scheduled in Fiscal Year 2029 (Sirota 2020). The plan is to buy 659 missiles—400 of which would be deployed, while the remainder will be used for test launches and as spares—at a price between $93.1 billion and $95.8 billion, increased from a preliminary $85 billion Pentagon estimate in 2016 (Capaccio 2020). These amounts do not include the costs for the new GBSD warhead––the W87-1––which is projected to cost up to $14.8 billion (Government Accountability Office 2020). The Air Force says the GBSD will meet existing user requirements but have the adaptability and flexibility to be upgraded through 2075 (US Air Force 2016). The new missile is expected to have a greater range than the Minuteman III, although it is unlikely that it will have enough range to target countries like China, North Korea, and Iran without overflying Russia.

The GBSD will be capable of carrying single or multiple warheads. The Air Force initially planned to equip the GBSD with life-extended versions of the existing W78 and W87 warheads. The modified W78 was known as Interoperable Warhead 1 (IW-1). But in 2018, the Air Force and National Nuclear Security Administration canceled the W78 upgrade and instead proposed a W78 Replacement Program using a W87-1 warhead. The new warhead will use a W87-like plutonium pit, “using a well-tested IHE [Insensitive High Explosive] primary design” (Energy Department 2018b). The new warhead will be incorporated into a modified version of the Mk21 reentry vehicle and be designated as the W87-1/Mk4A. In order to produce the W87-1 in time to meet the GBSD’s planned deployment schedule, the National Nuclear Security Administration has set itself an extremely ambitious production schedule that relies upon its ability to produce up to 80 plutonium pits per year by 2030. However, due to the agency’s consistent inability to meet project deadlines and its lack of a latent large-scale plutonium production capability, it is extremely unlikely that this 80-pit requirement will be met in time, meaning that W87-1 production and deployment will almost certainly be delayed (Government Accountability Office 2020; Institute for Defense Analyses 2019).

In October 2019, Lockheed Martin was awarded at $138 million contract to integrate the Mk21 reentry vehicle into the GBSD, beating out rivals Boeing, Raytheon, Northrop Grumman, and Orbital ATK (which Northrop Grumman now owns and has been renamed to Northrop Grumman Innovation Systems) (Lockheed Martin 2019). Because the W87-1/Mk21A will be bulkier than the current W78/Mk12A, the GBSD payload section would have to be wider to accommodate multiple warheads, and Northrup Grumman’s GBSD illustration shows a missile that is different than the existing Minuteman III, with a wider upper body and payload section (Kristensen 2019b).

The Air Force faces a tight construction schedule for the deployment of the GBSD. Each Launch Facility is expected to take seven months to upgrade, while each Missile Alert Facility will take approximately 12 months. The Air Force intends to upgrade all 150 Launch Facilities and eight of 15 Missile Alert Facilities for each of the three ICBM bases; the remaining seven Missile Alert Facilities at each base will be dismantled (US Air Force 2020a). Since each Missile Alert Facility is currently responsible for a group of 10 Launch Facilities, this reduction could indicate that each Missile Alert Facility could be responsible for up to 18 or 19 Launch Facilities once the GBSD becomes operational––which could have implications for the future vulnerability of the GBSD’s command and control system (Korda 2020). Once these upgrades begin, potentially as early as 2023, the Air Force must finish converting one Launch Facility per week for nine years in order to complete deployment by 2036 (Mehta 2020). It is expected that construction and deployment will begin at F. E. Warren between 2023 and 2031, followed by Malmstrom between 2025 and 2033, and finally Minot between 2027 and 2036.

As the GBSD gets deployed, the Minuteman IIIs will be removed from their silos and temporarily stored at their respective host bases––either F. E. Warren, Malmstrom, or Minot––before being transported to Hill Air Force Base, the Utah Test and Training Range, or Camp Navajo. The rocket motors will eventually be destroyed at the Utah Test and Training Range, while non-motor components will ultimately be decommissioned at Hill Air Force Base. To that end, five new storage igloos and 11 new storage igloos will be constructed at Hill Air Force Base and Utah Test and Training Range, respectively (US Air Force 2020a). New training, storage, and maintenance facilities will also be constructed at the three ICBM bases, which will also receive upgrades to their Weapons Storage Areas. The first base to receive this upgrade is F. E. Warren, where a groundbreaking ceremony for the new Weapons Storage and Maintenance Facility (also called the Weapons Generation Facility) was held in May 2019. Substantial construction began in spring 2020 and is expected to be completed in 2022 (Kristensen 2020b; US Air Force 2019d).

Just like in 2019, the Air Force conducted four Minuteman III flight-tests in 2020. The first test took place on February 5th, when a team of airmen derived from all three ICBM bases launched a Minuteman III from Vandenberg Air Force Base to the Reagan Test Site on Kwajalein Atoll in the Western Pacific. Unlike most routine Minuteman test launches––which seek to verify fleet-wide reliability by picking a missile at random from one of the ICBM bases—this Developmental Test Launch used a spare missile from storage to assess the flight worthiness of new or replacement parts. This was the second of four scheduled launches of this kind, with the first having been conducted in February 2019 (US Strategic Command 2020d). This was also the first Minuteman test launch from Vandenberg since that base became part of the new US Space Force.

The second test took place on August 4th, when a joint team of Air Force Global Strike Command airmen and Navy sailors launched a Minuteman III remotely using the Airborne Launch Control System aboard a Navy E6-B Mercury, from Vandenberg Air Force Base to the Reagan Test Site on Kwajalein Atoll in the Western Pacific. Notably, the test missile was equipped with three reentry vehicles, despite the fact that each deployed Minuteman III is only equipped with a single reentry vehicle (US Strategic Command 2020e). The test came only five days after the Trump administration’s arms control envoy tweeted a photo of himself observing a snap exercise at Minot Air Force Base involving a Minuteman equipped with three reentry vehicles (Billingslea 2020).

The third test took place on September 2nd, when a missile selected from Minot Air Force Base was launched from Vandenberg to the Reagan Test Site (Scully 2020).

The fourth and final test took place on October 29, when a missile selected from Minot Air Force Base was launched from Vandenberg to the Reagan Test Site (US Air Force 2020c). The test launch took place only one day after the conclusion of STRATCOM’s Global Thunder nuclear command and control exercise.

Nuclear-powered ballistic missile submarines

The US Navy operates a fleet of 14 Ohio-class ballistic missile submarines, of which eight operate in the Pacific from their base near Bangor, Washington, and six operate in the Atlantic from their base at Kings Bay, Georgia. Normally, 12 of the 14 submarines are considered operational, with the remaining two boats in a refueling overhaul at any given time. But because operational submarines undergo minor repairs at times, the actual number at sea at any given time is closer to eight or 10. Four or five of those are thought to be on “hard alert” in their designated patrol areas, while another four or five boats could be brought to alert status in hours or days.

Each submarine can carry up to 20 Trident II D5 submarine-launched ballistic missiles (SLBMs), a number reduced from 24 to meet the limits of the New START treaty. Since 2017, the Navy has been replacing the original Trident II D5 with a life-extended and upgraded version known as Trident II D5LE (LE stands for “life-extended”). The D5LE, which has a range of more than 12,000 km (7,456 miles), is equipped with the new Mk6 guidance system designed to “provide flexibility to support new missions” and make the missile “more accurate,” according to the Navy and Draper Laboratory (Naval Surface Warfare Center 2008; Draper Laboratory 2006). The D5LE upgrade will continue until all boats have been upgraded and will also replace existing Trident SLBMs on British ballistic missile submarines. The D5LE will also arm the new US Columbia-class and British Dreadnought-class ballistic missile submarines when they enter service. Instead of building a new ballistic missile, the Navy plans to do a second life-extension of the Trident II D5 to ensure it can operate through 2084 (Eckstein 2019).

Each Trident SLBM can carry up to eight nuclear warheads, but normally carry an average of four or five warheads, for an average load-out of approximately 90 warheads per submarine. The payload of the different missiles on a submarine are thought to vary significantly to provide maximum targeting flexibility, but all deployed submarines are thought carry the same combination. Normally, 900 to 950 warheads are deployed on the operational ballistic missile submarines, although the number can be lower due to maintenance of individual submarines. The New START data from October 2020, however, indicated there were 1,009 warheads deployed on 220 SLBM launchers, marking the first time since 2015 that the United States deployed more than 1,000 warheads on its submarines (State Department 2020a). As a result, we have increased the total number of deployed warheads in Table 1. Overall, SSBN-based warheads account for nearly 70 percent of all warheads attributed to the United States’ deployed strategic launchers under New START.

Three warhead types are deployed on SLBMs: the 90-kiloton enhanced W76-1, the 8-kiloton W76-2, and the 455-kiloton W88. The W76-1 is a refurbished version of the W76-0, which is being retired, apparently with slightly lower yield but with enhanced safety features added. The National Nuclear Security Administration announced in January 2019 that it has completed production of the W76-1 (Energy Department 2019a), a massive decade-long production of an estimated 1,600 warheads. The Mk4A reentry body that carries the W76-1 is equipped with a new arming, fuzing, and firing unit with better targeting efficiency than the old Mk4/W76 system (Kristensen, McKinzie, and Postol 2017).

The other SLBM warhead, the higher-yield W88, is currently undergoing a life-extension program that in May 2020 produced the first assembly of the W88 Alt 370 First Production Capability at the Pantex Plant––a process that addresses nuclear safety concerns and will ultimately support future life-extension options (NNSA 2020a).

In the final weeks of 2019, the Navy deployed a low-yield version of the W76-1 known as W76-2 on the USS Tennessee (SSBN-734). The W76-2 only uses the warhead fission primary to produce a yield of about 8 kilotons. The First Production Unit of the W76-2 was completed at the Pantex Plant on February 22, 2019 and reached Initial Operational Capability some time before the end of the fiscal year on September 30, 2019 (NNSA 2019). It is unknown exactly how many W76-2 warheads were produced; however, the NPR says it’s a “small number” (Department of Defense 2018, 54). We estimate that no more than 25 were ultimately produced, and that one or two of the 20 missiles on each SSBN will be armed with a single W76-2 warhead, while the remainder of the warhead slots will be filled with either the 90-kiloton W76-1 or the 455-kiloton W88 (Arkin and Kristensen 2020).

The United States is also planning to build a new SLBM warhead––the W93––which will be housed in the Navy’s proposed Mk7 aeroshell (reentry body). The House Appropriations Committee refused to fund the W93 program in the 2021 defense budget, and it remains unclear whether it will be included in the final budget or whether it would be championed by a potential future administration. If funded, the W93 would probably replace the W76-1 at some point in the 2040s.

The US sea-based nuclear weapons program also provides substantial support to the British nuclear deterrent. The missiles carried on the Royal Navy ballistic missile submarines are from the same pool of missiles carried on US ballistic missile submarines. The warhead uses the Mk4A reentry body and is thought be a slightly modified version of the W76-1 (Kristensen 2011b); the British government calls the Trident Holbrook (UK Ministry of Defence 2015). The Royal Navy also plans to use the new Mk7 for the replacement warhead it plans to deploy on its new Dreadnought submarines in the future. Despite a significant lobbying effort on the part of the United Kingdom––including an unprecedented letter to US Congress from the UK Minister of Defence asking it to support the W93 warhead––the program’s status is currently unsettled (Borger 2020).

Since the first deterrent patrol in 1960, US ballistic missile submarines have conducted approximately 4,180 deterrent patrols at sea. During the past 15 years, operations have changed significantly, with the annual number of deterrent patrols having declined by more than half, from 64 patrols in 1999 to 30 to 36 annual patrols in recent years. Most submarines now conduct what are called “modified alerts,” which mix deterrent patrol with exercises and occasional port visits (Kristensen 2013b). While most ballistic missile submarine patrols last around 77 days, they can be shorter—or, occasionally, can last significantly longer. In June 2014, for example, the Pennsylvania (SSBN-735) returned to its Kitsap Naval Submarine Base in Washington after a 140-day deterrent patrol, the longest patrol ever by an Ohio-class ballistic missile submarine. In contrast to the Cold War years, when the overwhelming majority of deterrent patrols took place in the Atlantic Ocean, today more than 60 percent of deterrent patrols normally take place in the Pacific, reflecting increased nuclear war planning against China and North Korea (Kristensen 2018).

Ballistic missile submarines normally do not visit foreign ports during patrols, but there are exceptions. Over a four-year period in the late 1970s and early 1980s, US submarines routinely conducted port visits to South Korea (Kristensen 2011a). Occasional visits to Europe, the Caribbean, and Pacific ports continued during the 1980s and 1990s. After Russia’s invasion of Ukraine in 2014, the Navy has started to conduct one or two foreign port visits per year. A visit to Scotland in 2015 appeared to be a warning to Russia and was described as a US Navy plan to make ballistic missile submarines more visible (Melia 2015). A highly publicized visit to Guam in 2016—the first visit to the island by a ballistic missile submarine since 1988—was a clear warning to North Korea. Visits continued in 2017, 2018, and 2019 to Scotland, Alaska, and Guam.

Design of the next generation of ballistic missile submarines, known as the Columbia-class, is well under way. This new class is scheduled to begin replacing the current Ohio-class ballistic missile submarines in the late 2020s. The Columbia class will be 2,000 tons heavier than the Ohio-class and will be equipped with 16 missile tubes rather than 20. The Columbia program, which is expected to account for approximately one-fifth of the Navy’s entire shipbuilding program during the mid-2020s to mid-2030s, is projected to cost $109.8 billion (Congressional Research Service 2020, 8). The lead boat in a new class is generally budgeted at a significantly higher amount than the rest of the boats, as it is longstanding Navy practice to incorporate the entire fleet’s design detail and non-recurring engineering costs into the cost of the lead boat. As a result, the Navy’s fiscal 2021 budget submission estimates the procurement cost of the first Columbia-class SSBN – the USS Columbia (SSBN-826) – at approximately $14.4 billion, followed by $9.3 billion for the second boat (Congressional Research Service 2020, 9). A $5.1 billion development contract was awarded to General Dynamics Electric Boat in September 2017, and construction of the first boat began on October 1, 2020––the first day of fiscal 2021. It is possible, however, that certain elements of construction will be delayed due to the ongoing COVID-19 pandemic, as the Columbia Program Officer noted in June 2020 that missile tube production had already been delayed by “about a couple of months” due to the pandemic (Eckstein 2020). General Dynamics expects to receive $75 billion in revenue over the life span of the Columbia-class project (Medici 2017).After years of development, construction of the first of 12 Columbia-class SSBNs will begin in 2021, with first deterrent patrol scheduled for 2031. (Image: US Navy).

The Columbia-class submarines are expected to be significantly quieter than the current Ohio-class fleet, due to the introduction of an electric-drive propulsion train that will turn each boat’s propellor with an electric motor––instead of louder mechanical gears. Additionally, the components of an electric-drive propulsion train can be distributed around the boat, increasing the system’s resilience and lowering the chances that a single weapon could disable the entire drive system (Congressional Research Service 2000, 20). The Navy has never built a nuclear-powered submarine with electric-drive propulsion before, which could ultimately create technical delays for a program that is already on a very tight production schedule (Congressional Research Service 2020, 19).

In October 2019, the Columbia program manager noted in a presentation that final ship arrangements for the new class of submarines had been completed on September 6, apparently a year ahead of schedule (Bartolomei 2019). The Navy’s revised schedule now indicates that the Ohio-class boats will begin going offline in fiscal 2027, around the same time that the first Columbia-class boat is scheduled to be delivered in October 2027. Sea trials are expected to last approximately three years, and the first Columbia deterrence patrol is scheduled for 2031 (Congressional Research Service 2020, 8). The Columbia deliveries will coincide with the Ohio-class boats being taken out of service, and the Navy projects that they will go from 14 boats to 13 in 2027, 12 in 2029, 11 in 2030, and 10 in 2037, before eventually climbing back to 11 in 2041 and the full complement of 12 boats in 2042 (US Navy 2019; Rucker 2019). The lead boat of the new Columbia-class submarine fleet will be designated the USS Columbia (SSBN-826), and the second boat will be designated the USS Wisconsin (SSBN-827). The rest of the Columbia-class submarine fleet has not yet been named (US Navy 2020a).

Compared with the previous year’s five test launches, only two Trident II D5LEs were test-launched in 2020. The tests took place on February 12 and 16 from the USS Maine (SSBN-741). The first launch was part of a Demonstration and Shakedown Operation (DASO-30) designed to test both the system and the crew’s readiness for operational deployment, and the second was intended to gather additional data on the weapon system’s reliability and accuracy. These launches marked the 177th and 178th successful test launches of the Trident II system since its introduction into the US arsenal in 1989 (US Navy 2020b; US Navy 2020c).

Demonstration and Shakedown Operations are conducted after an ballistic missile submarine completes its Engineering Refueling Overhaul (ERO)––a multi-year operation that takes place around the 20-year point for each boat. The overhaul consists of extensive structural repairs and the refueling of the boat’s nuclear reactor, and results in a 20-year life extension for each boomer. The Navy first completed the USS Ohio’s (SSBN-726) ERO in December 2005, and has since completed 16 additional overhauls, completing the USS Wyoming’s (SSBN-742) ERO in October 2020 (Department of Defense Inspector General 2018; Naval Sea Systems Command 2020). It is expected that the USS Wyoming will undergo a Demonstration and Shakedown Operation (DASO-31) next year. The final ballistic missile submarine to undergo an ERO is the USS Louisiana (SSBN-743), which began the overhaul process in August 2019 and is expected to be completed in late 2021 or early 2022 (Farley 2019). The Columbia-class SSBNs will not require nuclear refueling; as a result, their midlife maintenance operations will take significantly less time than their Ohio-class counterparts (Congressional Research Service 2020, 5).

Strategic bombers

The US Air Force currently operates a fleet of 20 B-2A bombers (all of which are nuclear-capable) and 87 B-52H bombers (46 of which are nuclear-capable). A third strategic bomber, the B-1, is not nuclear-capable. Of these bombers, we estimate that approximately 60 (18 B-2As and 42 B-52Hs) are assigned nuclear missions under US nuclear war plans, although the number of operational bombers is lower. The New START data from March 2019 counted 50 deployed nuclear bombers (12 B-2As and 38 B-52Hs) (State Department 2020a). The bombers are organized into nine bomb squadrons in five bomb wings at three bases: Minot Air Force Base in North Dakota, Barksdale Air Force Base in Louisiana, and Whiteman Air Force Base in Missouri. The new B-21 bomber program will result in an increase in the number of nuclear bomber bases.

Each B-2 can carry up to 16 nuclear bombs (the B61-7, B61-11, and B83-1 gravity bombs), and each B-52H can carry up to 20 air-launched cruise missiles (the AGM-86B). B-52H bombers are no longer assigned gravity bombs (Kristensen 2017b). An estimated 850 nuclear weapons, including 528 air-launched cruise missiles, are assigned to the bombers, but only about 300 weapons are thought to be deployed at bomber bases. The remaining 550 bomber weapons are thought to be in central storage at the large Kirtland Underground Munitions Maintenance and Storage Complex outside Albuquerque, New Mexico.

The United States is modernizing its nuclear bomber force by upgrading nuclear command and control capabilities on existing bombers; developing improved nuclear weapons (the B61-12 and the long-range standoff missile); and designing a new heavy bomber, the B-21 Raider.

Upgrades to the nuclear command and control systems that the bombers use to plan and conduct nuclear strikes include the Global Aircrew Strategic Network Terminal (Global ASNT)—a new high-altitude electromagnetic pulse–hardened network of fixed and mobile nuclear command and control terminals that provides wing command posts, task forces, munitions support squadrons, and mobile support teams with survivable ground-based communications to receive launch orders and disseminate them to bomber, tanker, and reconnaissance air crews. First delivery of the Global Aircrew Strategic Network Terminals was expected in May 2020, although it is unclear if this has since been completed (US Air Force 2018).

Another command-and-control upgrade involves a program known as Family of Advanced Beyond Line-of-Sight Terminals (FAB-T), which replaces existing terminals designed to communicate with the MILSTAR satellite constellation. These new, extremely high frequency terminals are designed to communicate with several satellite constellations, including Advanced Extremely High Frequency satellites. FAB-T will provide protected high–data rate communication for nuclear and conventional forces, to include what is officially called Presidential National Voice Conferencing. According to the Air Force (US Air Force 2019b), “FAB-T will provide this new, highly secure, state-of-the-art capability for [Department of Defense] platforms to include strategic platforms and airborne/ground command posts via MILSTAR, [Advanced Extremely High Frequency], and Enhanced Polar System (EPS) satellites. FAB-T terminals will also support the critical command and control … of the MILSTAR, [Advanced Extremely High Frequency], and EPS satellite constellations.”

The heavy bombers are also being upgraded with improved nuclear weapons. This effort includes development of the first guided, standoff nuclear gravity bomb, known as the B61-12, which is intended to replace all existing gravity bombs. The bomb will use a modified version of the warhead used in the current B61-4 gravity bomb. B61-12 integration drop tests have already been conducted from the B-2 bomber (and several tactical fighter jets). Approximately 480 B61-12 bombs, which appear to have earth-penetration capability (Kristensen and McKinzie 2016), are expected to cost a total of roughly $10 billion. The first production unit was initially scheduled for March 2020; however, in September 2019 a National Nuclear Security Administration official confirmed that both the B61-12 and the upgraded W88 warhead for the Trident II SLBM will likely face delays during production due to concerns over the longevity of its commercial off-the-shelf subcomponents (Gould and Mehta 2019). The First Production Unit (FPU) prototype of the B61-12 was completed on August 25, 2020 at the Pantex Plant (NNSA 2020b). The first real FPU is expected to roll off the production line in late 2021.

The Air Force is also developing a new nuclear air-launched cruise missile known as the long-range standoff (LRSO) missile. It will replace the AGM-86B air-launched cruise missile in 2030 and carry the W80-4 warhead, a modified version of the W80-1 used in the current air-launched cruise missile. In February 2019, the Nuclear Weapons Council authorized the Development Engineering phase (Phase 6.3) for the W80-4. The Production Engineering stage (Phase 6.4) is planned for December 2021 (Energy Department 2019b). A solicitation invitation to defense contractors in 2015 listed three potential options for the LRSO engine: First, a derivative subsonic engine that improves on current engine technology by up to 5 percent; second, an advanced subsonic engine that improves on current technology by 15 percent to 20 percent; and third, a supersonic engine (US Air Force 2015). In August 2017, the Air Force awarded 5-year contracts of $900 million each to Lockheed Martin and Raytheon to develop design options for the missile. After reviewing the designs, the Air Force in December 2019 cleared the two companies to continue development of the missile (Sirota 2019). The Air Force originally planned to down-select to a single contractor in fiscal 2022 during the awarding of the Engineering and Manufacturing Development contract; however, in April 2020, the Air Force selected Raytheon as the prime contractor for the LRSO (US Air Force 2020b). This was a relatively surprising move, as selecting a single-source contractor at this early stage could ultimately result in higher program costs.

In March 2019, the Air Force awarded Boeing a $250 million contract to integrate the future LRSO capability onto the B-52Hs, a process that is expected to be completed by the beginning of 2025 (Hughes 2019). Development and production are projected to reach at least $4.6 billion for the missile (US Air Force 2019a) with another $10 billion for the warhead (Energy Department 2018a).

The missile itself is expected to be entirely new, with significantly improved military capabilities compared with the air-launched cruise missile, including longer range, greater accuracy, and enhanced stealth (Young 2016). This violates the White House pledge from 2010 (White House 2010) that the “United States will not … pursue … new capabilities for nuclear weapons,” though the NPR from 2018 did away with such constraints.

Supporters of the LRSO argue that a nuclear cruise missile is needed to enable bombers to strike targets from well outside the range of the modern and future air-defense systems of potential adversaries, and to provide US leaders with flexible strike options in limited regional scenarios. However, critics argue that conventional cruise missiles, such as the extended-range version of the Joint Air-to-Surface Standoff Missile, can currently provide standoff strike capability, and that other nuclear weapons would be sufficient to hold the targets at risk. In fact, the conventional extended-range Joint Air-to-Surface Standoff Missile (JASSM-ER) is now an integral part of STRATCOM’s annual strategic exercises.

Unlike the current air-launched cruise missile, which is only carried by the B-52H bomber, the long-range standoff missile will be integrated on both the B-52H and new B-21 bombers (Kristensen 2013c). Warhead production is scheduled from 2025 through 2031. The Air Force plans to buy 1,000 missiles (Reif 2015), but there will only be enough warheads for about half of those. The excess missiles are intended to be used as spares and for test flights over the course of the weapon’s 30-year service life. Moreover, several hundred of the existing air-launched cruise missiles were converted to conventional missiles (AGM-86C/D) and the US Air Force Global Strike Command has previously indicated that it intends to develop a conventional version of the LRSO (Wilson 2015).

But given the deployment of several new long-range conventional cruise missiles and the development of even more advanced versions, it remains to be seen if the Air Force can persuade Congress to also pay for a conventional version of the LRSO. Indeed, the Air Force has replaced the AGM-86C/D conventional air-launched cruise missile with the extended-range conventional Joint Air-to-Surface Standoff Missile. If Congress will not pay for conventional LRSOs, it can probably be assumed that the plan to buy 1,000 missiles can be reduced by several hundred.

Development of the new B-21 Raider next-generation heavy bomber continues at Northrop Grumman, with the preliminary design review receiving approval in early 2017 and the first test vehicle currently in production. The B-21 is scheduled to make its first flight no earlier than 2022 from its production facility in Palmdale, California, to Edwards Air Force Base (Wolfe 2020). The B-21 is expected to enter service in the mid-2020s to gradually replace the B-1B and B-2 bombers during the 2030s, and it is expected that the Air Force will procure at least 145 of the new bombers at an estimated cost of $550 million per plane to increase the total bomber force from 175 to 220 aircraft (Tirpak 2020).

The B-21 bomber program will expand the number of US nuclear bomber bases. (Image: US Air Force).

The Air Force announced in March 2019 that the B-21 bombers will first be deployed at Ellsworth Air Force Base (South Dakota), followed by Whiteman Air Force Base (Missouri) and Dyess Air Force Base (Texas) “as they become available” (US Air Force 2019c). The upgrade of the non-nuclear B-1 bases to the nuclear B-21 bomber will increase the number of bomber bases with nuclear weapons storage facilities from two bases today (Minot AFB and Whiteman AFB) to five bases by the 2030s (Barksdale AFB will also regain nuclear storage capability) (Kristensen 2020d). Further details about the B-21 program, including updated cost estimates, are still shrouded in secrecy; however, like all previous bomber programs, the costs will most likely increase.

The B-21 is very similar in design to the B-2 but is expected to be slightly smaller and have a reduced weapons capability. The B-21 will be capable of delivering both the B61-12 guided nuclear gravity bomb and the LRSO, as well as a wide range of non-nuclear weapons, including the Joint Air-to-Surface Standoff cruise missile.

Nonstrategic nuclear weapons

The United States has one type of nonstrategic nuclear weapon in its stockpile, the B61 gravity bomb. The weapon exists in two modifications: the B61-3 and the B61-4. A third version, the B61-10, was retired in September 2016. Approximately 230 tactical B61 bombs of all versions remain in the stockpile. About 100 of these (versions -3 and -4) are thought to be deployed at six bases in five European countries: Aviano and Ghedi in Italy; Büchel in Germany; Incirlik in Turkey; Kleine Brogel in Belgium; and Volkel in the Netherlands. This number has declined since 2009 partly due to reduction of operational storage capacity at Aviano and Incirlik (Kristensen 2015, 2019c). The remaining 130 B61s stored in the United States are for backup and potential use by US fighter-bombers in support of allies outside Europe, including northeast Asia.

The Belgian, Dutch, German, and Italian air forces are assigned nuclear strike missions with US nuclear weapons. Under normal circumstances, the nuclear weapons are kept under the control of US Air Force personnel; their use in war must be authorized by the US president. The Belgian and Dutch air forces currently use the F-16 aircraft for the nuclear missions, although both countries are in the process of obtaining the F-35A to eventually replace their F-16s. The Italian Air Force uses the PA-200 Tornado for the nuclear mission but is in the process of acquiring the F-35A. Like the Tornados, the nuclear F-35As will be based at Ghedi Air Base, which is currently being upgraded. Germany officially rejected the F-35A in early 2019 and is instead planning on purchasing Eurofighter Typhoons as well as F-18 Super Hornets, which reportedly have easier nuclear certification processes (NTV 2020). However, a formal decision on Germany’s aircraft procurement will not be made until at least 2022 (Zeitvogel 2020).

At least until 2010, Turkey was still using F-16s for the nuclear mission, although it is possible that the mission has since been mothballed. In 2019, the Trump administration also halted delivery of F-35As to Turkey––some of which were intended to be used in the nuclear mission––because of its plans to acquire the Russian S-400 air-defense system (DeYoung, Fahim, and Demirjian 2019). Concerns were raised about the security of the nuclear weapons at the Incirlik base during the failed coup attempt in Turkey in July 2016, and the chairman of the Senate Foreign Relations Subcommittee for Europe stated in September 2020 that “our presence, quite honestly, in Turkey is certainly threatened,” and further noted that “we don’t know what’s going to happen to Incirlik” (Gehrke 2020). Despite rumors in late 2017 that the weapons had been “quietly removed” (Hammond 2017), reports in 2019 that US officials had reviewed emergency nuclear weapons evacuation plans (Sanger 2019) indicated that that there were still weapons present at the base. The numbers appear to have been reduced, however, from up to 50 to approximately 20. If the United States decided to withdraw the remaining nuclear weapons from Incirlik, it could probably do so with a single C-17 transport aircraft from the 4th Airlift Squadron at Joint Base Lewis-McChord in Washington—the only unit in the Air Force that is qualified to airlift nuclear weapons.

NATO states that do not host nuclear weapons can still participate in the nuclear mission as part of conventional supporting operations, known as SNOWCAT (Support Nuclear Operations With Conventional Air Tactics).

NATO is working on a broad modernization of the nuclear posture in Europe that involves upgrading bombs, aircraft, and the weapons storage system. The B61-12 is estimated to be 12 feet long, weighing approximately 825 pounds, and is designed to be air-launched in either ballistic or gravity drop modes (Baker 2020). The B61-12 will be deployed to Europe beginning in 2022–2024, at which point the older B61-3 and B61-4 bombs will be returned to the United States. The B61-12 will use the nuclear explosive package of the B61-4, which has a maximum yield of approximately 50 kilotons and several lower-yield options, but it will be equipped with a guided tail kit to increase accuracy and standoff capability, which will allow strike planners to select lower yields for existing targets to reduce collateral damage. The increased accuracy will give the tactical bombs in Europe the same military capability as strategic bombs in the United States. Although the B61-12 has not been designed as a designated earth-penetrator, it does appear to have some limited earth-penetration capability, which increases its ability to hold at risk underground targets (Kristensen and Matthew 2016).An F-35A carries out a test drop of a B61-12 guided nuclear bomb over Nevada in August 2020. The B61-12 will replace all US strategic and tactical nuclear gravity bombs and also be supplied to NATO allies. (Image: US National Nuclear Security Administration).

In March 2020, the F-15E became the first aircraft to be certified to operate the B61-12, after completing the last in a series of six compatibility tests at Nellis Air Force Base and the Tonopah Test Range (Baker 2020). In addition to the F-15E, integration of the B61-12 on B-2, F-16, and PA-200 aircraft is well under way, and the F-35A—with its incoming Block 4 software patch— is expected to become nuclear-certified with the B61-12 in 2024–2026. The Block 4 software will be patched into existing F-35As in six-month increments, starting in 2023 (Roblin 2019).

NATO is life-extending the Weapons Storage Security System––which involves upgrading command and control, as well as security––at the six active bases (Aviano, Büchel, Ghedi, Kleine Brogel, Incirlik, and Volkel) and one training base (Ramstein).

In addition to the modernization of weapons, aircraft, and bases, NATO also appears to be increasing the profile of the dual-capable aircraft posture. In October 2020, for example, at the start of the Steadfast Noon nuclear deterrence exercise, NATO Secretary General Jens Stoltenberg visited Volkel Air Base in the Netherlands. Stoltenberg said that the exercise, which included over 50 aircraft, was “an important test for the Alliance’s nuclear deterrent” (NATO 2020b). Likewise, in June 2020, the 31st Fighter Wing at Aviano Air Base conducted the first “Elephant Walk” ever to display all aircraft in a single visual show of force of its capability to “deter and defeat any adversary who threatens U.S. or NATO interests” (US Air Force 2020d).

Having reached 50 ratifications in October 2020, the Treaty on the Prohibition of Nuclear Weapons (TPNW) will officially enter into force on January 22, 2021. It is unclear whether the treaty will have an effect on the status of NATO’s nuclear posture––and specifically the forward-deployment of US nuclear weapons on European NATO territory––however, public opinion in Belgium, Germany, Italy, and the Netherlands is firmly opposed to hosting US nuclear weapons (International Campaign to Abolish Nuclear Weapons 2018). To that end, some host country parliaments have already taken actions that challenge the future of US nuclear weapons on their soil; in January 2020, a motion to “draw up, as soon as possible, a roadmap aiming at the withdrawal of nuclear weapons on Belgian territory” was narrowly defeated 74–66 in the Belgian parliament (Galindo 2020). It is possible that the entry-into-force of the TPNW could prompt similar resolutions to be debated and voted upon in other nuclear hosting nations, which explains why the United States tried in vain to persuade other countries to withdraw their ratifications, only a week before the TPNW reached 50 ratifications (Lederer 2020).

The 2018 Nuclear Posture Review has recommended rapid development of a nuclear nonstrategic submarine-launched cruise missile to recreate a capability to deploy such a weapon in support of NATO (and Pacific) allies. A previous cruise missile was retired in 2011. The new weapon would likely be intended for deployment on attack submarines. It is doubtful that the incoming Biden administration will continue the project.