Fitting Hypersonic Weapons into the Nuclear Arms Control Regime

April 1, 2020
White House Archives
Cameron Tracy
Kendall Fellow

I recently compared the capabilities of hypersonic weapons—an emerging missile technology that sends warheads gliding through the atmosphere at high speeds—to existing ballistic missiles. Despite the hype surrounding this new technology, the challenges of hypersonic flight severely limit their performance. Reporting on the various advantages hypersonic missiles might offer is often overblown.

Still, hypersonic weapons could be a game-changer when it comes to nuclear arms control policy. The New Strategic Arms Reduction Treaty (New START), the only active treaty limiting the deployment of US and Russian nuclear weapons, does not explicitly restrict hypersonic missiles—an omission that turns out to be intentional (see below). Either nation could conceivably take advantage of this gap in the treaty’s coverage to expand their nuclear-capable missile forces, unfettered by the carefully constructed arms control regime that protects global nuclear stability.

Fortunately, this perilous scenario can be easily averted, so long as the United States and Russia take steps to ensure that arms control policy keeps pace with emerging missile technologies.

New START’s hypersonic gap

New START sets limits on the deployment of US and Russian nuclear forces. Because these nations possess the vast majority of the world’s nuclear weapons, it constitutes the bedrock of modern nuclear arms control.

The treaty’s core provisions were carefully crafted to address the complexities of nuclear weapons technology. It does not directly limit the number of nuclear warheads either nation may possess, as these are difficult to track and account for. Rather, it focuses on the nuclear warhead delivery systems—ground-launched missiles, submarine-launched missiles, and heavy bomber aircraft—by which these destructive payloads can be carried intercontinental distances. New START limits the number of these systems each nation may possess (up to 800) and deploy (up to 700), as well as the number of warheads that can be mounted on them (up to 1,550).

Most contemporary hypersonic missiles consist of “boost-glide” systems launched by ground-based rockets. For this class of armament, New START applies specifically to  “a weapon delivery vehicle that has a ballistic trajectory over most of its flight path.” Ballistic trajectories are determined by a projectile’s initial velocity and the force of gravity, which pulls the object down as it travels (in atmospheric flight, air resistance will play a role as well). This results in a simple, arcing flight path. Ballistic missiles follow such flight paths, with the exception of brief periods immediately after launch and before impact.

Hypersonic weapons follow flight paths distinct from those of ballistic missiles. Once accelerated to high speeds, they take advantage of aerodynamic forces to generate lift, gliding through the atmosphere like an airplane. Since these gliding vehicles spend most of their flights on non-ballistic trajectories, they are not captured by New START’s specific phrasing.

Yet the treaty’s coverage is a complicated issue. The only intercontinental-range hypersonic system deployed to date, Russia’s Avangard, is currently mounted on a rocket also used for their intercontinental ballistic missiles, to which New START does apply. So, while not explicitly covered, the Avangard is currently subject to de facto limits. While better than nothing, these limits could be easily circumvented if either nation chose to deploy hypersonic weapons on a new type of rocket, one that is not also used for ballistic missiles. This indirect coverage makes for a precarious situation when it comes to nuclear weaponry.

Exclusion by design

This omission of hypersonic weapons from New START’s coverage was intentional. At the time the treaty was formulated in 2009-2010, the United States was in the midst of a push to develop its first hypersonic missiles, and sought to ensure that the agreement would not hinder these new weapons.

According to James Miller, then the Principle Deputy Under Secretary of Defense for Policy, this US position was “made clear in the New START treaty negotiations” with Russian counterparts. He later told Congress he was “confident” that these weapons “would not be accountable as ‘new kinds of strategic offensive arms,’ for the purposes of the treaty” and would thus not be subject to limitations.

In ratifying New START, the Senate made clear that the US interpretation of the treaty precluded “any prohibition on the deployment of such systems.” Furthermore, plans to launch hypersonic weapons on the new Minotaur IV rocket, distinct from those used for US intercontinental ballistic missiles, would have circumvented the de facto limitations discussed earlier. In other words, when it came to New START, hypersonic weapons were off the table.

In contrast, Russian negotiators were incensed by what they saw as a ploy to shirk limitations by substituting a new type of weapon for the ballistic missiles around which the treaty was designed. Russian Minister of Foreign Affairs Sergey Lavrov stated at the time that they “find unacceptable the unilateral American interpretation of the treaty” under which prospective US hypersonic missiles “shall not be regarded as new types of strategic offensive weapons covered by the treaty.”

Despite this discord, the issue mattered little for most of New START’s ten-year term, since neither nation had managed to develop a successful hypersonic missile.

A new start for hypersonic arms control

Yet, as New START approaches its ten year renewal deadline, the contours of this policy conflict have shifted. The United States does not, as it might have once expected, hold a monopoly on hypersonic weaponry. Russia reports that its hypersonic, nuclear-armed Avangard, first announced by President Putin in 2018, entered service in late 2019 (although further testing may be required prior to full-scale deployment). In contrast, US hypersonic missile programs remain years away from deployment.

Concerned about what this might mean for national security, US officials have recently undergone a dramatic reversal of opinion with respect to the inclusion of hypersonic missiles in arms control agreements. Secretary of Defense Mark Esper now perceives an urgent need to “capture the new Russian strategic weapons” in an updated New START.

Fortunately, Russia has held to its stance that hypersonic weapons should be subject to the same bilateral limitations as are regular intercontinental-range ballistic missiles. In 2019 Vladimir Leontiev, the Russian Foreign Ministry’s Deputy Director for Nonproliferation and Arms Control, said “there are no big problems with Avangard…because it is an optional warhead for an ICBM [intercontinental ballistic missile] of the corresponding type, to which the treaty applies, too. The Avangard will enter the treaty very smoothly.” Shortly thereafter, Russia provided US inspectors access to the missile, just as they do for regular intercontinental-range ballistic missiles under New START’s protocols.

Still, this inclusion is based on Avangard’s sharing of a rocket with Russian intercontinental ballistic missiles. If, for example, Russia decided to field this hypersonic vehicle on a new rocket, the resulting missile would not be explicitly subject to New START’s limitations.

Keeping pace with technological change

While it does not currently address hypersonic weapons in full, New START serves as a cornerstone in the architecture of nuclear arms control, enhancing global security. With the February 2021 renewal deadline fast approaching, the United States and Russia should work together to ensure that there is no lapse in their decades-long tradition of mutual restraint.

The advent of hypersonic weaponry introduces a new complication to the arms control landscape. Fortunately, New START is a flexible treaty. It includes specific provisions for dealing with emerging weapon systems via its Bilateral Consultative Commission. And, as Russia has demonstrated, hypersonic weapons can be incorporated into existing arms control protocols.

With the United States and Russia suddenly in agreement on the need to limit the deployment of hypersonic missiles, now is an ideal time to explicitly and transparently address these weapons under the New START framework. Doing so would ensure that nuclear arms limitations remain robust, even as tensions flare. With the clock ticking on renewal, neither nation can afford to let a hypersonic arms race get in the way of a proven instrument of global security.

Image caption: Former President Barack Obama signed the instrument of ratification of the New START Treaty in the Oval Office on Feb. 2, 2011. The only active treaty limiting the deployment of US and Russian nuclear weapons, New START does not explicitly restrict hypersonic missiles. With the February 2021 renewal deadline fast approaching, the US and Russia should work together to ensure no lapse in their decades-long tradition of mutual restraint. 

The featured image in this blog is courtesy the White House Archives.