Hypersonic weapons, and particularly hypersonic cruise missiles, sound terrifying. They can travel at Mach 5 speed—five times the speed of sound or more than 3,800 miles per hour—or faster, and have great maneuverability, making detection and intercept extremely difficult. Hypersonic weapons likely would surpass any existing missile defense technology and could reach nearly any coordinate on Earth within 30 minutes. Characterized as a “game changer” or potentially “unstoppable,” militaries could equip these fast and elusive weapons with conventional or even nuclear warheads. Raising further concern for U.S. officials, Russia and China seemingly enjoy a significant advantage in this technology, having prioritized the development and testing of these weapons over the last several years, whereas until recently, the United States has not.

Despite this considerable hype, the effect of hypersonic weapons on military strategy ultimately will likely  be much more muted than currently assumed: Key engineering questions remain unresolved, and while the technological capabilities of these weapons sounds consequential, they are less alarming when contextualized alongside the threat of existing missiles and nuclear weapons, which possess even greater capacity for destruction. Further, there is good reason to believe that these weapons will do little to alter existing balances of power or create defense vulnerabilities for the U.S. that are not already present.

The larger issue concerning both hypersonic weapons, as well as existing nuclear weapons, is the lack of political will to pursue policies and to uphold international agreements that prohibit or limit such weapons. This criticism applies to all three States that currently have hypersonic weapons: the U.S., Russia, and China. Rather than funneling millions (and potentially billions) of dollars into an unnecessary arms race, these three States would better serve their own security interests, as well as those of the international community, by committing to an open and verifiable information-sharing and weapon-inspection process. Previously, such an agreement between the U.S. and the Soviet Union — the Intermediate-Range Nuclear Forces (INF) Treaty — led to the destruction of nearly 2,700 missiles in only three years. The recent U.S. withdrawal from that treaty, and the Russian treaty violations that prompted this decision, are deeply problematic, but the INF still provides valuable lessons for how States can limit these weapons without sacrificing their military advantage.

State of Play

On March 19, the Department of Defense (DoD) successfully tested a hypersonic glide body. Launched from the Pacific Missile Range Facility in Kauai, Hawaii, the Common-Hypersonic Glide Body (C-HGB) flew at a hypersonic speed to a designated impact point. After the test, DoD officials noted that the launch “serves as a major milestone towards its goal of fielding hypersonic combat capabilities in the early to mid-2020s.”

Russia conducted a successful test of its Avangard hypersonic glide vehicle on December 27, 2019. Russian President Vladimir Putin boasted that the Avangard was “invulnerable to intercept by any existing and prospective missile defense means of the potential adversary.” While U.S. officials pushed back against Russia’s near invincible characterization of the Avangard vehicle, analysts note that Russia currently leads in the development of this technology.

China too is developing hypersonic weapons and became the first country to announce a “hypersonic missile,” the DF-17, which it highlighted during its 2019 National Day military parade. (Although characterized as a hypersonic missile, the DF-17 is a medium-range ballistic missile designed specifically to launch hypersonic glide vehicles.) Public information about the DF-17 is sparse and some experts question whether this weapon provides China additional capability compared to its existing missile arsenal, particularly its formidable collection of ballistic missiles. Nonetheless, China’s pursuit of hypersonic weapons has made its neighbors uneasy, and Japan is now developing its own hypersonic weapons, including an anti-ship missile that it hopes to field by 2026.

Currently, only the U.S., Russia, and China have hypersonic weapons. These weapons fall into two categories: hypersonic cruise missiles, or glide vehicles that are mounted to a ballistic missile, such as the Russian Avangard or the U.S. C-HBG. The glide vehicles rely on the ballistic missile to loft the glider to the very top of the atmosphere, where it could maneuver for thousands of miles before being directed at its target. Weapons experts note that the speed and maneuverability of these weapons is difficult to overstate and may be such that existing radars simply do not detect them.

For the U.S., the C-HGB will serve as the base of its hypersonic weapons delivery. While each military service will employ this base, they will develop individual weapon systems to match use, such as whether the launching platform accommodates a ship launch (Navy) or a land-based launch (Army). The successful test in March helped DoD officials temper criticism that the U.S. was falling behind Russia and China in this field. Hypersonic weapons are one of the highest development priorities for DoD, which hopes to field an offensive hypersonic weapon by the mid-2020s. More specifically, the Army hopes to field a land-based hypersonic missile by 2023; the Navy, a ship-launched missile also by 2023, and a submarine-launched missile by 2024; and the Air Force, an air-launched missile by 2022.

Advantage Russia and China?

The advances of Russian and Chinese hypersonic weapons development and testing raised serious concerns within DoD. In March 2018, Air Force Gen. John Hyten, then the commander of U.S. Strategic Command (STRATCOM), gave a candid assessment of Russian and Chinese progress on these weapons when he testified before the Senate Armed Services committee. Hyten would not admit a Russian or Chinese advantage, but he did make several concessionary remarks and in a CNN interview following the hearing stated, “I don’t want to put a who’s winning the race, I’ll just say there is a race.”

Michael Griffin, the current undersecretary of Defense for Research and Engineering and previously NASA administrator under President George W. Bush, has been even more forceful in calling for a U.S. response to Russian and Chinese advances. In December 2018, Griffin noted, “In the last year, China has tested more hypersonics weapons than we have in a decade.” More recently, in March 2020, Griffin argued that the U.S. would need to field large numbers of hypersonic glides to compete with Russia and China.

Despite these somewhat dire pronouncements, experts disagree as to whether these weapons are indeed the “game changer” that some officials and analysts claim. Michael Unbehauen worked as a planner and commander in STRATCOM during his military career and recently argued that hypersonic weapons are not yet a game changer and treating them as such downplays existing defense vulnerabilities. Unbehauen notes,

Of course, research is needed to develop ways to defend against these hypersonic weapons as soon as possible. Despite this, one must remember that current hypersonic weapon capabilities are by far nowhere close to giving their operators a clear military advantage.

Another perspective concludes that the threat posed by hypersonic weapons is real, but misplaced, and that aggressively reacting to the Russian and Chinese advances unnecessarily escalates an avoidable arms race. James Acton, a physicist and hypersonic weapons expert at the Carnegie Endowment for International Peace, questioned the utility of hypersonic weapons as early as 2014, when he concluded:

The United States has spent 10 years and a billion dollars on a weapon that has no defined mission. And in the meantime, American research and development efforts have prompted Russia and China to pursue similar weapons of their own that could be deployed in as little as a decade, starting an arms race that could place the continental United States at risk.

In contrast, former CIA analyst Timothy Walton countered that hypersonic glides do have a clearly defined objective, namely to address “China’s rapidly advancing military capabilities, including its massive arsenal of intermediate-range missiles.”

Cameron Tracy, writing for the Union of Concerned Scientists, provides the most critical assessment of hypersonic weapons, criticizing their “fantastic depiction” and concluding that they “offer few advantages over existing missile technology.” Tracy argues that the supposed capabilities of hypersonic weapons are often “distorted, exaggerated, or simply untrue,” noting that intercontinental ballistic missiles (ICBMs) travel nearly 20 times the speed of sound and many accounts of hypersonic weapons do not consider how the air resistance that these weapons would encounter traveling through the atmosphere would reduce their speed. Tracy also argues that existing technology, including early warning satellites from the 1970s, would detect hypersonic launches just as well as they detect other weapons, such as ballistic missiles. Finally, he finds that claims of increased vulnerability are overblown and that U.S. missile defenses are not designed to withstand a missile attack from Russia or China now (nor vice versa)—a point that then-Secretary of Defense James Mattis also made in 2018. Thus, Tracy concludes that hypersonic weapons will not alter strategic considerations, but if framed and accepted as a national imperative, could enrich weapons manufacturers and the defense industry.

In the last few years, the response to hypersonic weapons certainly seems like a boon for the defense industry. Lockheed Martin received $2.5 billion in contracts to develop hypersonic weapons in April 2019 and Dynetics Technical Solutions received a $351.6 million contract to produce C-HGB prototypes. Further, a Congressional Research Services (CRS) report published in March shows that DoD requested $3.2 billion for all hypersonic-related research in FY 2021, a significant increase from its $2.6 billion request in FY 2020.

However, this rapid increase in requested funding could also be due to the U.S. spending nearly two decades on foreign interventions, occupation, and counterinsurgency operations. According to Unbehauen, “While the United States was consumed with fighting wars in Iraq and Afghanistan, Russia and China developed their anti-access/area denial (A2/AD) capabilities and hypersonic weapons programs.” Likewise, Lt. Cmdr. Ryan Hilger, a Navy engineering duty officer, recently concluded,

At the dawn of hypersonic weapons, the Navy is woefully unprepared. Nearly a decade of budgetary cuts and nearly two decades of operations in support of the global war on terror have exhausted the fleet and slowed technological development.

Escalation without Regulation?

As the development and testing of hypersonic weapons continues, U.S. policymakers and military leaders must consider how international law limits these weapons or constrains their use. But, despite the destructive capability of these weapons, international arms control law currently does little to regulate their development, testing, or production.

Until recently, for the U.S. and Russia, the most logical treaty for limiting or prohibiting hypersonic weapons would have been the INF Treaty. However, the Trump administration formally withdrew the U.S. from the INF treaty on Aug. 2, 2019, citing Russia’s continued violation of the treaty. Previous administrations, as distinct as President Ronald Reagan and President Barack Obama, faced similar situations, but decided to remain a party to the treaty and press Soviet and Russian counterparts for better adherence.

Reagan and Soviet leader Mikhail Gorbachev signed the INF Treaty on December 9, 1987, and the U.S. Senate ratified the treaty the following June. The treaty banned all land-based ballistic and cruise missiles, nuclear and conventional, as well as missile launchers, with ranges between 500 and 5,550 kilometers. Despite initial skepticism, the treaty led to the destruction of thousands of missiles and allowed for on-site inspections in both the United States and Russia, building trust between adversaries during a politically charged time. More recently, critics argued that the INF Treaty had outlived its usefulness, particularly as U.S. claims that Russia was violating the treaty intensified and that it did not address China’s continued amassment of intermediate-range missiles. The latter point is especially important, as this bilateral treaty did not apply to China, which now possesses a sophisticated collection of missiles and shows little interest in joining international agreements to limit or regulate these weapons.

Without the INF Treaty, the only remaining nuclear arms control treaty between the U.S. and Russia is New START (Strategic Arms Reduction Treaty), which itself expires in February 2021. This treaty also provides for weapons inspections and allowed U.S. experts to inspect the Avangard in late November 2019, about a month before Russia successfully tested the weapon. As noted in the March CRS report, this treaty would not apply to hypersonic gliders or missiles since these weapons do not fly on a ballistic trajectory for more than 50 percent of their flight, but Article V of the treaty allows the parties to consider restricting new arms through the treaty’s Bilateral Consultative Commission. For now, the U.S., Russia, and China have stated that they will not equip hypersonic weapons with nuclear warheads, though Russia and to a lesser extent China have not been entirely clear on this point. Like the INF Treaty, New START is a bilateral treaty and does not apply to China or other States.

Negotiating a new international arms control treaty that would address hypersonic weapons, whether through a test ban, moratorium, or some other restrictive measure, is the best option, but almost certainly a political non-starter given the prevailing nationalist sentiments and constant refrain of great power competition. At the same time, China continues to build a formidable missile arsenal, while showing no signs of reconsidering its opposition to entering arms control treaties. Coupled with mutual distrust between the U.S. and Russia, the likelihood of an arms treaty between these three States to limit hypersonic weapons hovers just above zero. Accordingly, Quincy Institute analyst Steven Simon concluded,

The biggest threat from hypersonics is that they come at a time when the world’s arm control treaties are falling apart. We need a multilateral agreement to limit hypersonic arsenals and their use, but unfortunately, the United States, which would have to take the lead in orchestrating the negotiation of such an agreement, is uninterested in any deals that might tie its hands.

Without an international agreement prohibiting or regulating the development and testing of these weapons, the lawfulness of their use falls under public international law, generally, and international humanitarian law (IHL), specifically. For IHL, the most relevant consideration is weapon reviews. States parties to Additional Protocol I to the Geneva Conventions (AP I) are obligated by Article 36 to determine by “the study, development, acquisition or adoption of a new weapon” whether the weapon’s use would “in some or all circumstances, be prohibited by this Protocol or by any other rule of international law applicable to the High Contracting Party.” Whether customary international law requires States to conduct weapon reviews, and would thus apply to all States regardless of whether they are party to AP I, is debatable, but this requirement likely has not yet attained customary international law status.

Russia and China are parties to AP I, but neither State provides adequate information to assess their weapon reviews. The U.S. is not a party to AP I, but it conducts robust weapon reviews as a matter of policy. More generally, States are often unwilling to provide specific information concerning weapon reviews, given the sensitivity of this information and how it pertains to legitimate national security concerns. Nonetheless, this lack of information makes it difficult to verify whether states are complying with their legal requirements.

It is also doubtful that hypersonic weapons raise legal concerns that IHL does not already address. Fundamental legal requirements, such as distinction, proportionality, and the prohibition on unnecessary suffering would still apply and any weapon that could not meet these requirements would be unlawful per se. But, even the worst IHL offenders typically do not employ such weapons; rather, it is the unlawful use of lawful weapons that frequently constitutes IHL violations. And even good faith mistakes made by well-trained operators can result in terrible loss of life.

The early success of the INF Treaty led to a significant reduction of nuclear weapons and allowed for the world’s two most militarily powerful states to verify that its rival was complying with the treaty. Through information sharing and onsite inspections, this process gradually built trust and lessened tensions. The net result was a safer world and a more secure international order. U.S., Russian, and Chinese leaders would do well to apply this model to hypersonic weapons rather than needlessly escalating an unnecessary arms race.

Image: A common hypersonic glide body (C-HGB) launches from Pacific Missile Range Facility during a Defense Department flight experiment, Kauai, Hawaii, March 19, 2020. Photo: U.S. Navy