As hypersonic weapons have become a growing component of the global arsenal of nuclear warheads, U.S. policymakers and analysts have started debating the implications for strategic stability, missile defense and the long-term composition of the Pentagon’s own stockpile.

Three of the world’s five largest nuclear powers—Russia, China and France—have fielded or plan to field nuclear weapons on hypersonic glide vehicles (HGV) or cruise missiles, according to official sources.

Russia’s defense ministry declared the Avangard HGV operational in December 2019. The Avangard, which some analysts have speculated may be closer to a maneuvering reentry vehicle than a hypersonic glider, entered service with the 13th Missile Division at Dombarovsky. The Avangard is integrated on a Russian intercontinental ballistic missile (ICBM) called UR-100N, which NATO designates as the SS-19 Mod 4.

• Fate of U.S. triad linked to nuclear HGV debate
• Analysts agree U.S. stockpile does not need hypersonics
• First French HGV test scheduled later this year

In China, the People’s Liberation Army Rocket Force (PLARF) is “enhancing its credible and reliable capabilities of nuclear deterrence and counterattack,” stated the country’s latest defense white paper, in 2019. China does not share any details about its current and future nuclear stockpile, but a top U.S. defense official testified to the Senate Armed Services Committee in February 2020 that the PLARF is “testing” an intercontinental-range HGV similar to the Avangard.

The statement by Gen. Terrence O’Shaughnessy, who then led the North American Aerospace Defense Command, cannot be verified. Asked to elaborate months later by Aviation Week, O’Shaughnessy declined and referred a reporter to his written testimony to the Senate. But the U.S. military’s statement implies that China has integrated an HGV on an ICBM, such as the DF-5, DF-31 or DF-41, and is testing the new weapon.

As the U.S. Air Force prepares for the first test of a conventional air-launched HGV weapon in March, the French defense ministry plans to begin flight testing an HGV by year-end. French officials have not declared a follow-on operational role for the Experimental Maneuvering Vehicle (V-MaX) program, but an obvious candidate would be to augment or replace the navy’s nuclear deterrent force of submarine-launched ballistic missiles.

France also boasts the world’s only acknowledged program to develop an air-launched hypersonic cruise missile with a nuclear warhead. The ASN4G program is scheduled to replace the high-supersonic ASMP-A cruise missile launched by the air force’s Dassault Rafale fighters by the early-to-mid-2030s.

The idea of using a rocket-boosted HGV to deliver a nuclear warhead dates back to the early 1940s. German scientists developed a concept for the manned Silbervogel HGV to deliver a nuclear payload on the U.S. homeland. Neither the German nuclear weapon nor the Silbervogel moved beyond the laboratory stage, but the latter served as the inspiration for the U.S. Air Force’s Boeing X-20 Dyna-Soar a decade later. As questions lingered into the early 1960s about the accuracy of ICBMs, using a manned HGV to deliver a nuclear payload was considered a prudent hedge.

In the end, reentry vehicles on ICBMs proved to be accurate enough for the nuclear deterrence mission for several decades. Although the speed and maneuverability of HGVs are often highlighted, a reentry vehicle released by an ICBM travels faster and maneuvers to evade defensive interceptors. The key difference between an HGV and ICBM is the flight profile. An ICBM boosts a reentry vehicle into space, where it cruises above the atmosphere until it is nearly over the target. By contrast, an HGV reenters the atmosphere almost immediately, then pitches up and begins a long glide within the atmosphere, where it can use a relatively low altitude and aerodynamic maneuvering to hide from land-based sensors.

Despite those performance differences, the appeal of HGVs and hypersonic cruise missiles for a nuclear role is not universal. The U.S. and UK stand notably apart among the five largest nuclear powers for having no plans to deploy an HGV or scramjet-powered cruise missile with a nuclear warhead. Although the U.S. fields nuclear warheads on ICBM- and submarine-launched reentry vehicles, subsonic cruise missiles and bombs, Defense Department policy prohibits dual-use or purely nuclear versions of conventional HGVs and hypersonic cruise missiles.

The Pentagon’s prohibition has not stopped all talk of nuclearizing the future U.S. hypersonic arsenal, however. Last August, the Air Force Nuclear Weapons Center published a request for information that included concepts for a future nuclear long-range ICBM, but the document was removed from the government’s acquisition website after a reporter asked about it. Three months later, Gen. Timothy Ray, the head of Air Force Global Strike Command, broached the possibility of fielding an HGV if policymakers ever decide to remove one leg of the nuclear triad. Asked to elaborate on those thoughts in late February, Ray said that would require a policy decision “well above me.”

“At the end of the day, the hypersonic glide vehicle conversation in the nuclear piece is not part of the conversation I’m in,” Ray adds. “So I’m going to keep my eyes and my energy focused on executing the programs that still remain the cornerstone of our security.”

The balance created by the nuclear triad of ICBMs, air-launched cruise missiles and submarine-launched ballistic missiles underpins the Pentagon’s prohibition of nuclear hypersonic weapons. Adding a more survivable element to the nuclear arsenal does not change the strategic calculation because neither Russia nor China has the power to defeat a massive attack from the U.S. side. But that position could be revisited if the U.S. strategic balance changes.

Some nuclear analysts are quick to add a temporal caveat upon any mention of support for the Defense Department’s non-nuclear hypersonic weapons policy.

“For me today, in 2021, I think conventional is the name of the game for the United States,” Thomas Mahnken, president of the Center for Strategic and Budgetary Assessments, said during an event in February hosted by The Aerospace Corp.

“Could that change in the future? I guess, you know, for a whole bunch of reasons,” Mahnken added. “But I think the overwhelming case for the United States is conventional.”

In a follow-up email, Mahnken wrote that he had no specific developments in mind that could change the need for a conventional-only posture for U.S. hypersonic weapons in the near term.

“Of course, any number of developments on the U.S., Russian or Chinese sides could change that equation over the mid-to-long term, which is why I qualified my statement,” Mahnken wrote. “I think it makes sense to develop and deploy only non-nuclear hypersonic weapons now, [but] I would not forswear their development in the future.”

Notably, the Russians possess an arsenal of long-range nuclear weapons that is similar in makeup and volume to the U.S. stockpile, but they came to a different conclusion. The Avangard gives the Russians a weapon designed to evade the U.S. ballistic missile defense system, even though that system is not capable of defending the homeland from a mass nuclear strike.

Analysts debated the reasons for Russia’s decision during a recent Aerospace Corp. webinar. Cameron Tracy, Kendall Fellow for the Global Security program at the Union of Concerned Scientists, thinks Russia developed a nuclear HGV over concerns that the U.S. might develop a credible defense against ICBMs. Dean Wilkening, a retired scientist at the Johns Hopkins University Applied Physics Laboratory, speculates that development of the Avangard may reveal Russia’s concerns about the reliability of its existing nuclear arsenal. Ultimately, Jill Hruby, former director of Sandia National Laboratories, argues that Russia’s nuclear hypersonic program may be a positive development for strategic stability.

“They are pretty paranoid about our missile defenses,” Hruby says. “So the belief that the Avangard will confuse our missile defenses actually is stabilizing. At some level, their deployment of their systems helps them believe in their nuclear deterrent capability. So I think the fact that Russia has deployed the system is not something we should be overly concerned with. We should not do anything in return. I think that the U.S. position—that we don’t need nuclear-tipped hypersonic boost glide vehicles—is correct.”