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March 13, 2020
Defense Primer: Hypersonic Boost-Glide Weapons
The U.S. Department of Defense is pursuing two types of
States would likely detect the booster’s launch, as it would
hypersonic weapons technologies: boost-glide systems that
for the launch of any ballistic missile, but it would not be
place a maneuverable glide vehicle atop a ballistic missile
able to predict the HGV’s flight path. In addition, although
or rocket booster, and cruise missiles that would use high-
an HGV launched by a rocket booster would reach its target
speed, air-breathing engines known as scramjets to travel to
far more quickly than a warhead delivered by an aircraft or
hypersonic speeds. This In Focus addresses only the first of
subsonic cruise missile (in minutes instead of hours), it
these technologies.
would not travel faster than a ballistic reentry vehicle.
However, it would be more difficult to predict the intended
The Pentagon’s FY2021 budget request for hypersonic-
target and to direct missile defense interceptors toward the
related research is $3.2 billion—up from $2.6 billion in the
attacking HGV.
FY2020 request—including $206.8 million for hypersonic
defense programs. This increased funding and statements
Hypersonic Boost-Glide Programs
from Pentagon officials demonstrate growing support for
weapons that could attack priority targets promptly and
United States
with improved accuracy without facing defeat by an
When the United States began to assess the military utility
adversary’s air or missile defense systems. Pentagon
of hypersonic boost-glide weapons in the early 2000s, it
officials have also expressed concerns about advances in
sought to develop longer-range systems that could reach
hypersonic weapons technologies in Russia and China, and
deep into an adversary’s territory to attack defended,
on the potential threats to U.S. forces, allies, and territory.
hardened, and time-urgent targets. (For an overview of the
history of U.S. programs, see CRS Report R41464,
Characteristics of Hypersonic
Conventional Prompt Global Strike and Long-Range
Glide Vehicles
Ballistic Missiles: Background and Issues, by Amy F.
Hypersonic glide vehicles (HGVs), like all weapons
Woolf.) More recently, the Pentagon has increased funding
delivered by medium- and longer-range rocket boosters, can
and accelerated development programs for shorter and
travel at speeds of at least Mach 5, or about 1 mile per
intermediate-range boost-glide systems that could conduct
second. The key difference between missiles armed with
prompt attacks against heavily defended targets in regional
HGVs and missiles armed with ballistic reentry vehicles
conflicts. The Department of Defense (DOD) is developing
(i.e., those that travel on a ballistic trajectory throughout
hypersonic weapons under the Navy’s Conventional Prompt
their flight) is not their speed, but their ability to maneuver
Strike program, as well as through several Air Force, Army,
and change course after they are released from their rocket
and DARPA programs. (Details on these programs can be
boosters. In addition, although it is not necessary, many
found in CRS Report R45811, Hypersonic Weapons:
concepts for the delivery of HGVs presume that the
Background and Issues for Congress, by Kelley M. Sayler.)
boosters will launch along a flatter, or depressed, trajectory
than standard ballistic missiles, and will release their gliders
Unlike Russia and China, the United States is not
at a lower altitude of flight (see Figure 1).
developing HGVs for use with nuclear warheads. As a
result, U.S. gliders may require greater accuracy and will be
Figure 1.Flight Trajectory of Ballistic Missiles vs.
more technically challenging to develop than nuclear-armed
Hypersonic Boost-glide Weapons
Chinese and Russian systems.
Russia
Russia’s HGV, known as Avangard, is equipped with a
nuclear warhead and deployed on SS-19 long-range land-
based ballistic missiles. While SS-19 missiles can carry six
nuclear warheads on a ballistic trajectory, reports indicate
that they will deploy with only one Avangard HGV.
Avangard reportedly features onboard countermeasures and
will be able to maneuver in flight so that it can evade U.S.
ballistic missile defenses. Russia conducted successful tests
Source: The Economist.
of Avangard 2016 and 2018. On December 27, 2019, the
Russian military announced that it had activated two SS-19
Taken together, the HGVs’ novel trajectory and
missiles equipped with Avangard.
maneuverability in flight would complicate a U.S. effort to
detect, track, and defend against an attack. The United
https://crsreports.congress.gov
Defense Primer: Hypersonic Boost-Glide Weapons
Russia views the Avangard system as a part of its nuclear
programs and expanded them to include short-, medium-,
retaliatory capability, ensuring that Russian missiles could
and long-range systems.
penetrate U.S. ballistic missile defenses. According to the
Pentagon’s 2019 Missile Defense Review, the United States
When asked about this dynamic in February 2020, Admiral
relies on nuclear deterrence, not ballistic missile defenses,
Charles Richard, the commander of USSTRATCOM, noted
to counter Russia’s long-range missile forces. Nevertheless,
that there “is a competition, just like any other military
in March 2018, President Putin stated that Russia had
competition.” But he did not characterize it as an arms race.
pursued HGV technologies in response to the U.S. 2002
He noted that the United States was developing
withdrawal from the 1972 Anti-ballistic Missile Treaty.
technologies needed to meet U.S. national objectives, and
Some U.S. analysts, however, have noted that the Russia
he noted that he expected the United States to be successful
could use the Avangard as part of a first strike, even in the
in meeting its security goals. Others have noted that the
absence of U.S. ballistic missile defenses, to attack critical
same is true for Russia and China; each is developing
targets quickly. Others have assessed that Russia is likely to
HGVs to meet their own security interests, not to counter or
deploy Avangard in small numbers, so it will add little to
match the U.S. development of HGVs. Specifically, both
Russia’s existing nuclear force structure.
seem to be responding to concerns about U.S. ballistic
missile defense programs.
China
China has developed an HGV known as the DF-ZF
Game-Changing Technology?
(previously referred to as the WU-14) and has tested it at
Some analysts have asserted that the speed, accuracy, and
least nine times since 2014. U.S. defense officials have
maneuverability of hypersonic boost-glide weapons will
stated that the HGV may be capable of performing
fundamentally change the character of warfare. The acting
“extreme maneuvers” during flight, which would allow it to
Secretary of the Navy, Thomas Modly, made this case in
evade U.S. ballistic missile defenses. Unclassified reports
January 2020 when he noted that these technologies “have
indicate this glider would likely be equipped with
already changed the nature of the battlespace” and that they
conventional warheads, and when mated with the DF-17
“can destabilize the global security environment and pose
booster, could travel to ranges of 1,800-2,500 kilometers.
an existential threat to our nation.” Others question this
assessment. They note that boost-glide systems can reach
China is also developing the DF-41 long-range
their targets more quickly than other maneuverable systems,
intercontinental ballistic missile, which, according to a
like aircraft and subsonic cruise missiles. But adversaries
2014 report by a U.S. Congressional Commission, could
armed with ballistic missiles have long been able to attack
carry a nuclear hypersonic glide vehicle. Gen. Terrence
U.S. forces, allies, and territory, even without maneuvering
O’Shaughnessy, the commander of U.S. Northern
warheads. Consequently, they argue that there is nothing
Command, seemed to confirm this assessment in February
new about the threat from nuclear-armed HGVs, when
2020, when he testified that “China is testing a [nuclear-
compared with other nuclear-armed missiles, and nothing
armed] intercontinental-range hypersonic glide vehicle …
existential about a threat from conventionally armed HGVs.
which is designed to fly at high speeds and low altitudes,
complicating our ability to provide precise warning.”
Crisis Instability?
Boost-glide systems could accelerate the pace of warfare
Some contend that China has prioritized HGV development
and create incentives to strike first in a crisis. If the United
to counter “specific security threats from increasingly
States and potential adversaries develop these systems to
sophisticated U.S. military technology.” This includes both
strike promptly against high-value targets protected by
U.S. hypersonic weapons that could threaten strikes against
missile defenses, each side may believe it has to strike first,
China’s nuclear arsenal and supporting infrastructure, and
and strike fast, to achieve its objectives. This dynamic—
U.S. missile defense deployments that could then limit
often referred to as crisis instability—could provoke the
China’s ability to conduct a retaliatory strike against the
start of a conflict even if neither party to the crisis initially
United States. In this framework, nuclear-armed HGVs on
planned to strike first.
long-range missiles would ensure that China had the ability
to retaliate after a U.S. attack, even if the United States
DOD is seeking to address the potential threats posed by
were to expand its ballistic missile defense capabilities.
hypersonic boost-glide weapons with programs developing
HGVs on medium-range missiles would aid China’s efforts
defensive systems to track and engage them. Experts
to threaten U.S. assets in the Indo-Pacific region,
disagree on the cost and technological feasibility of this
particularly when faced with growing U.S. regional missile
approach. Policymakers may also consider mechanisms to
defense capabilities.
ban or limit the deployment of these weapons to avoid the
crisis instabilities created by their short time of flight. On
Arms Race Dynamics?
the other hand, nations might be unwilling to agree to limit
Many analysts have characterized the ongoing U.S.,
these weapons without corresponding limits on missile and
Russian, and Chinese development of HGVs and boost-
air defenses.
glide weapons as an arms race because each nation seems to
be competing to be the first to deploy these systems. Some
Kelley M. Sayler, Analyst in Advanced Technology and
argue that the United States is falling behind in this contest
Global Security
because Russia and China have both displayed operational
Amy F. Woolf, Specialist in Nuclear Weapons Policy
systems. Others argue that the United States is leading, and
may be escalating the race because it has accelerated its
IF11459
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Defense Primer: Hypersonic Boost-Glide Weapons
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