High Speed, Low-Yield: A U.S. Dual-Use Hypersonic Weapon

September 17, 2020
original (7)

Should the United States put nuclear warheads on hypersonic missiles? For 20 years, Washington has answered “no” by excluding nuclear weapons from its prompt strike and hypersonic weapons programs. In order to close gaps in U.S. theater deterrence and assurance capabilities, it is time to consider a change of course. Theater capabilities currently depend too much on aircraft and low-observable technology, the advantages of which are being eroded by advancements in adversary air defenses. Meanwhile, low-yield Trident missiles invite escalation and put strategic deterrence assets at risk.

One U.S. hypersonic program — the Common Hypersonic Glide Body — relies on neither aircraft nor low-observability. It ought to be a prime candidate for becoming a dual-use weapon with conventional and low-yield nuclear variants. There are counterarguments, which I will address and welcome others to raise, but even once they are fairly considered, the case for nuclear-tipped hypersonic missiles is persuasive. It would serve U.S. interests — namely, by improving U.S. theater deterrence, diversifying its assurance capabilities, and gaining leverage for future arms control agreements.

The Hypersonic Connection

Concerns about using hypersonic weapons for nuclear delivery often focus on the strategic level of war, where fears of large-scale instability and national vulnerability reside. However, the numerous intercontinental delivery systems already possessed by China, Russia, and the United States mean strategic hypersonic missiles produce only a marginal change in each other’s strategic vulnerability. While the Kremlin cites U.S. missile defenses as motive for its Avangard missile and other programs, the performance and cost realities of U.S. missile defenses make effective interdiction unrealistic for any large-scale nuclear strike, whether delivered by hypersonic or ballistic warheads. China is less transparent but has similar motivations, with added concerns rooted in its smaller arsenal and perceptions of U.S. ambiguity on mutual vulnerability — a condition that Beijing may try to impose with an Avangard-like system, as mentioned by Gen. Terrence O’Shaughnessy. Against the fear of a first strike, each of the three nations cultivates second-strike capabilities that may be more vulnerable to widespread cyber attack than a finite number of long-range hypersonic weapons. Even if one concedes a stabilizing role for strategic hypersonic weapons in China and Russia, adding them to an already robust U.S. modernization plan seems unnecessary given limited resources.

 

 

There is a more compelling case for the significance of hypersonic weapons at the theater level, where the logic of speed and defeating air and missile defenses applies to everyone. History has shown the enduring value of rapid effects delivered from multiple firing positions and in conjunction with other forces. This is certainly true for conventional munitions, as well as theater nuclear delivery and therefore deterrence. It is reflected in Russia’s avowedly dual-capable Kinzhal and, potentially, its Tsirkon, as well as perhaps China’s DF-17. In contrast, the United States has ruled out nuclear hypersonic capabilities for a variety of reasons, including presumptions of U.S. conventional dominance and theater nuclear sufficiency as well as programmatic momentum. This conventional-only approach was the right decision in the early 2000s, but that restraint may no longer be in the best interests of the United States and its allies.

Gaps in U.S. Theater Nuclear Deterrence

Theater deterrence is not just a microcosm of strategic deterrence. It involves U.S. interests alongside those of regional nations, which are both party and victim to potential conflicts. Escalation concerns are prominent and nuanced, incentivizing in-theater capabilities in order to forgo launching strikes from one’s homeland and risking retaliation there. This includes “low-yield” weapons. Although not formally defined, the phrase is useful in classifying weapons whose explosive power is generally tens of kilotons in TNT equivalent or less. To be clear, the bombs at Hiroshima and Nagasaki were estimated at 16 kilotons and 21 kilotons, respectively, making both “low-yield” weapons in today’s parlance. Low-yield weapons are clearly still devastating, which is why former Secretary of Defense James Mattis told Congress that there is no “such thing as a ‘tactical nuclear weapon.’ Any nuclear weapon used any time is a strategic game-changer.” While critics disagree, proponents argue that low-yield weapons facilitate deterrence by presenting adversaries with a more credible threat. This logic vis à vis Russia’s particular dedication to low-yield weapons is why they escaped complete elimination from the U.S. inventory before being reinvigorated by the 2018 Nuclear Posture Review.

The United States currently has three low-yield weapons for theater nuclear deterrence: the B61 gravity bomb, one type of air-launched cruise missile, and the low-yield W76-2 warhead on Trident submarine launched ballistic missiles. The U.S nuclear modernization plan will replace its air-launched cruise missiles from the 1970s with the Long-Range Standoff weapon and will see the return of a nuclear sea-launched cruise missile. These new delivery systems reflect a broader modernization theme: The United States does not need more nuclear weapons. It needs better ones, suitable for 21st century deterrence. However, the current approach perpetuates three vulnerabilities in U.S. theater deterrence.

The first is dependence on low observability (i.e., stealth) technology and tactics. Delivering a B61 or an air-launched cruise missile relies on the aircraft, the weapon, or both staying off an enemy’s radar. The same may be true for future sea-launched cruise missiles. Low-observable techniques are effective today and for the immediate future, but they are increasingly jeopardized by advanced air defense systems from Russia and China, along with the future systems they will inevitably deploy. The ongoing battle between signature and sensor will eventually meet an irreducible minimum, likely in favor of the sensor, at which point low observability may become moot.

The second is the escalatory problem of using U.S. strategic Trident missiles for theater purposes. Aside from the W76-2’s potential vulnerability to missile defenses, using a Trident means adversary leaders will not know if their country has been targeted with a high-yield or low-yield weapon until after impact. This action thus entails gambling, or at best an educated guess, on whether those decision-makers will wait that long before initiating their own retaliatory actions.

Third, U.S. theater deterrence and assurance are overly reliant on aircraft and easily targeted airfields. Until 2019, the Intermediate-Range Nuclear Forces Treaty prohibited development of relevant ground-based weapons. At sea, decommissioning the nuclear Tomahawk variants removed attack submarines and surface warships from the deterrence chessboard. The W76-2 is responsive to this but with the escalatory issues mentioned above. So are future sea-launched cruise missiles, but potentially beholden to low-observable designs. With U.S. ballistic missile submarines rarely visiting foreign ports and new nuclear-armed maritime cruise missiles still up to 10 years away, in-theater manifestations of U.S. nuclear assurances are limited to U.S. aircraft in allied airfields or air space willing to permit them.

A New Role for the Common Hypersonic Glide Body

Although U.S. doctrine retains the prerogative of nuclear first use in defense of vital interests, a limited retaliatory action remains the most probable scenario. This makes it critical that low-yield delivery systems succeed when only one or a few weapons must be guaranteed to reach their objective. Among U.S. hypersonic programs, the Common Hypersonic Glide Body is the best option for a dual-use design that closes gaps in U.S. theater deterrence. This leaves the Air-launched Rapid Response Weapon to continue on track as a conventional system and likely the first U.S. weapon to become operational. It also may provide more payload capacity compared to the Hypersonic Air-breathing Weapon Concept, another air-launched missile. Furthermore, cooperative development of the Common Hypersonic Glide Body by the Army and Navy facilitates joint familiarity, logistics, and options for conventional-nuclear integration within theater contingency plans.

Target Access

Rather than stealth, hypersonic missiles defeat air defenses through a combination of speed, trajectory, and maneuverability. Even when hypersonic defense becomes feasible (at costs potentially unbearable for China and Russia), short flight times mean successful interception requires a nearly flawless detect-to-engage sequence. Against future air defenses, the Common Hypersonic Glide Body would be more credible for theater nuclear delivery than slower, low-observable cruise missiles while saving dual-capable aircraft for future missions, to include a potentially ongoing conventional fight. Additionally, the high-energy impact physics of hypersonic glide vehicles mean it would likely exceed the penetration capability of a B61 without relying on a ballistic trajectory. While its accuracy has not been disclosed, its origin in delivering precise conventional effects means it is surely accurate enough for low-yield weapons.

Scalable Presence

A dual-use approach capitalizes on the ground and maritime integration already planned for the Common Hypersonic Glide Body, diversifying U.S. theater deterrence and assurance capabilities with non-aircraft options. Virginia-class submarines and potentially Zumwalt-class destroyers offer high-mobility options for unilaterally deploying these weapons to either the European or Pacific theater. This is already planned for conventional variants as part of the Navy’s Intermediate Range Conventional Prompt Strike program. With allied coordination, port visits from these vessels could help signal U.S. commitment to extended deterrence while alleviating the political burdens allies would face in permanently hosting U.S. weapons. Should an ally see that burden become more tolerable or more necessary, ground-mobile firing units armed with this system atop the Army’s Long Range Hypersonic Weapon would provide options not constrained to airfields. Even if not immediately dispatched, simply having this family of deployable systems could help in assuring allies and cautioning adversaries, or reinforcing a secondary theater while the United States fought a major conflict elsewhere.

Safeguarding Trident

Low-yield variants of the Common Hypersonic Glide Body aboard Virginia-class submarines should be a replacement capability for low-yield W76-2 warheads. Retiring the W76-2 would return U.S. Trident missiles to their strategic-only role aboard Ohio- and Columbia-class submarines. This would reduce escalatory risks by alleviating (though not eliminating) an adversary’s Trident discrimination problem. It would also reduce an adversary’s incentives to target U.S. strategic platforms in pursuit of its own theater objectives, helping safeguard U.S. ballistic missile submarines as the most survivable leg of the country’s strategic triad. The United States could then credibly assert that attacks on these submarines would be considered attacks on its strategic deterrent. While similar benefits could accrue from sea-launched cruise missiles, the Common Hypersonic Glide Body does not rely on low-observable designs and may be able to reach initial operational capability faster and more efficiently.

Concerns

Making a bold course change like the one suggested here warrants careful consideration of the risks for both action and inaction. The risk of inaction is straightforward: a potential deterioration in U.S. deterrence and assurance capabilities (the same sentiment that has motivated broader U.S. modernization efforts). The risks of action, however, are more specific when it comes to adopting a dual-use Common Hypersonic Glide Body.

Entanglement and Escalation

Entangling conventional and nuclear capabilities comes with risks. For one, exquisite weapons make exquisite targets in a crisis. Some fear that an agitated adversary might purposefully or inadvertently strike a nuclear-armed hypersonic missile, prompting the United States to cross the nuclear threshold first. Second, dual-use hypersonic missiles replace an adversary’s Trident discrimination problem with one of pre-launch ambiguity between nuclear and conventional warheads — a problem complicated by the compressed decision timeline of hypersonic flight. These issues lead to further concerns that hypersonic weapons will incentivize postures and reactions that heighten escalation risks. However, like dual-use cruise missiles and aircraft, the Common Hypersonic Glide Body is a theater system that is more resilient against the use-it-or-lose-it fears underpinning that argument. Strikes against it would garner a strong response, but U.S. strategic deterrence would not be jeopardized and theater deterrence would be sustained by the portfolio of theater weapons that this hypersonic capability is meant to complement. Moreover, Russia has already introduced this threat, and the United States should turn its attention to deterring Moscow from leveraging it as an asymmetric, potentially coercive, advantage. Warhead ambiguity may even be beneficial by providing political flexibility to allies hosting these systems or inducing hesitancy in an adversary considering whether to strike a potential nuclear weapon, thus enhancing deterrence. Alternatively, ambiguity can be sacrificed to mitigate these concerns by restricting nuclear capabilities to identifiable units (especially on land).

Strategic Overlap

U.S adversaries may still perceive dual-use hypersonic missiles as threatening their strategic deterrence capabilities. Similar arguments could be mounted for many theater deterrence weapons the United States has previously deployed, from cruise missiles to W76-2s. This is one among many reasons China, Russia, and the United States safeguard their second-strike capabilities. It is also a reason theater deterrence relies on a different set of weapons and targets: to keep the cataclysmic power of strategic forces in reserve, and to keep national leaders in command. Furthermore, Moscow and Beijing already seem to fear U.S. conventional hypersonic weapons, which they believe convey first-strike advantages unencumbered by the nuclear taboo. Adding a low-yield capability to the Common Hypersonic Glide Body adds little on the margin of concerns driven by its conventional attributes but adds much to the ledger for deterring conflict overall.

Costs

Making the Common Hypersonic Glide Body a dual-use system is a more efficient use of limited funds as well as common infrastructure and logistics once operational. Gen. Dave Goldfein, who will retire on Oct. 1, recently stated that this is the first time the United States is modernizing its nuclear and conventional enterprises at the same time, and that “[t]he current budget does not allow you to do both.” Adding a proposal like this runs the risk of being a fiscal non-starter. However, the Common Hypersonic Glide Body is not a new program — it already has development funding for the delivery systems and a conventional warhead. The new component would be integrating a low-yield capability. Given the expected capabilities of its naval variant, one solution may be to forgo developing a replacement for nuclear sea-launched cruise missiles and utilize those funds to cover nuclear integration. It would also be a potentially less expensive route to strengthening theater deterrence compared with increasing the U.S. bomber fleet beyond original modernization requirements.

Arms Control and Arms Racing

Shifting to a dual-use design should be acknowledged for what it is: a failure of arms control and an incremental step of arms racing prompted by U.S. adversaries. It reflects the fact that the United States is already engaged in deterring a Russian force that has retained, modernized, and produced so many low-yield weapons that they allegedly outnumber the United States’ eight to one (1,830 to 230). Russia broke faith with the Intermediate-Range Nuclear Forces Treaty long before the Trump administration was elected, and has repeatedly rejected attempts to negotiate arms control parameters for its low-yield weapons. In the Pacific, reports that China is expanding its arsenal are pulling an ever-present nuclear subtext to the foreground and raising questions about what capabilities may yet come to underscore Beijing’s revisionist foreign policy.

U.S. low-yield weapons responsive to threats posed by Russia do risk being seen as a threat that Beijing must in turn respond to. Rather than counting on endless restraint by the United States, Chinese leaders should see this as a natural consequence of the multipolar world they themselves advocate and be willing to safeguard their regional interests through arms control. Yet Beijing has completely refused official engagement and at this point, “countless Track II dialogues with China are not a substitute.” After 20-plus years of a worthy and laudable arms control effort, the reality of this situation should be acknowledged and reflected in the U.S. force posture before progress can be made. As Lt. Gen. Robert P. Ashley Jr. noted, “the resurgence of great power competition is a geopolitical reality. It is the mindset Russia and China have embraced, the mindset that is guiding their approach to nuclear modernization and investment.”

The United States does not need to engage in an open-ended, expensive race to superiority. But in order to deter, it needs to ensure that its arsenal is fit for purpose in defeating an adversary locally. Both Russia and China would likely object to dual-use hypersonic missiles, calling their adoption a destabilizing move by the United States. This argument is hypocritical and false but expected — and to some degree desired: Washington should want Moscow and Beijing to react with some apprehension. Their reaction would acknowledge Washington’s signal of commitment to deterring their revisionist ambitions and defending U.S. allies. Their reaction would also reflect the fact that assured delivery for the United States means assured risk to their interests and security, giving both of them increased incentives to come to the negotiating table. This pressure point alone might not be decisive, but using it to complicate their decision space would be useful in pursuing trilateral arms control solutions to replace the Intermediate-Range Nuclear Forces Treaty or respond to the low-yield lacunae in New START — solutions that are beneficial to the stability and security of all three nations.

To Hype or Not to Hype (America’s Nuclear Arsenal)?

A dual-use Common Hypersonic Glide Body would close gaps in U.S. theater deterrence capabilities and offer scalable deployment options to assure allies. It would give the United States a tool for assured delivery of conventional and low-yield warheads that hedges against erosion of U.S. advantages in low-observable technology. Both variants could be deployed unilaterally and clandestinely at sea aboard submarines, or overtly in cooperation with allies. With its ground and maritime variants, shifting the Common Hypersonic Glide Body to a dual-use design would provide the United States with leverage and flexibility for future arms control efforts. Just as President Vladimir Putin and General Secretary Xi Jinping learned important lessons through the 1990s and early 2000s, their future successors are learning lessons now that will shape their ambitions and policy preferences for the 2030s and beyond. Statecraft remains the preferred solution, but the United States should back its diplomats with the right military tools so that they can navigate today’s competitive environment and shape the future of European and Pacific deterrence.

 

 

Alan Cummings is a recent master’s graduate from Tufts University’s Fletcher School of Law and Diplomacy and a 2020 member of the Center for Strategic and International Studies Nuclear Scholars Initiative. He served over 10 years on active duty with the U.S. Navy before transitioning to the Navy Reserve. The views expressed here are his own and in no way represent any institution with which he is affiliated.

Image: U.S. Army