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Updated November 14, 2022
Defense Primer: Hypersonic Boost-Glide Weapons
The U.S. Department of Defense (DOD) is pursuing two
for the launch of any ballistic missile, but it would not be
types of hypersonic weapons technologies: boost-glide
able to predict the HGV’s flight path. In addition, although
systems that place a maneuverable glide vehicle atop a
an HGV launched by a rocket booster would reach its target
ballistic missile or rocket booster, and cruise missiles that
far more quickly than a warhead delivered by an aircraft or
would use high-speed, air-breathing engines known as
subsonic cruise missile (in minutes instead of hours), it
scramjets to travel to hypersonic speeds. This In Focus
would not travel faster than a ballistic reentry vehicle.
addresses only the first of these technologies.
However, it would be more difficult to predict the intended
The Pentagon’s FY2023
target and to direct missile defense interceptors toward the
budget request for hypersonic-
attacking HGV.
related research is $4.7 billion—up from $3.8 billion in the
FY2022 request. 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 Navy, Air Force, Army, and DARPA all
(i.e., those that travel on a ballistic trajectory throughout
maintain hypersonic weapons programs. (Details on these
their flight) is not their speed, but their ability to maneuver
programs can be found in CRS Report R45811, Hypersonic
and change course after they are released from their rocket
Weapons: Background and Issues for Congress, by Kelley
boosters. In addition, although it is not necessary, many
M. Sayler.)
concepts for the delivery of HGVs presume that the
Unlike Russia and China, the United States is not
boosters will launch along a flatter, or depressed, trajectory
developing HGVs for use with nuclear warheads. As a
than standard ballistic missiles, and will release their gliders
result, U.S. gliders may require greater accuracy and will be
at a lower altitude of flight (see Figure 1).
more technically challenging to develop than nuclear-armed
Figure 1. Flight Trajectory of Ballistic Missiles vs.
Chinese and Russian systems.
Hypersonic Boost-Glide Weapons
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
of Avangard in 2016 and 2018. On December 27, 2019, the
Russian military announced that it had activated two SS-19
Source: CRS image based on an image in “Gliding missiles that fly
missiles equipped with Avangard.
faster than Mach 5 are coming,” The Economist, April 6, 2019.
Russia views the Avangard system as a part of its nuclear
Taken together, the HGV’s novel trajectory and
retaliatory capability, ensuring that Russian missiles could
maneuverability in flight would complicate a U.S. effort to
penetrate U.S. ballistic missile defenses. According to the
detect, track, and defend against an attack. The United
Pentagon’s 2022 Missile Defense Review, the United States
States would likely detect the booster’s launch, as it would
relies on nuclear deterrence, not ballistic missile defenses,
https://crsreports.congress.gov
Defense Primer: Hypersonic Boost-Glide Weapons
to counter Russia’s long-range missile forces. Nevertheless,
When asked about this dynamic in February 2020, Admiral
in March 2018, President Putin stated that Russia had
Charles Richard, the commander of U.S. Strategic
pursued HGV technologies in response to the U.S. 2002
Command, noted that there “is a competition, just like any
withdrawal from the 1972 Anti-ballistic Missile Treaty.
other military competition.” But he did not characterize it as
Some U.S. analysts have noted, however, that Russia could
an arms race. He noted that the United States was
use the Avangard as part of a first strike, even in the
developing technologies needed to meet U.S. national
absence of U.S. ballistic missile defenses, to attack critical
objectives and that he expected the United States to be
targets quickly. Others have assessed that Russia is likely to
successful in meeting its security goals. Others have noted
deploy Avangard in small numbers, so it will add little to
that the same is true for Russia and China; each is
Russia’s existing nuclear force structure.
developing HGVs to meet its own security interests, not to
counter or match the U.S. development of HGVs.
China
Specifically, both seem to be responding to concerns about
China has developed an HGV known as the DF-ZF
U.S. ballistic missile defense programs.
(previously referred to as the WU-14) and has tested it at
least nine times since 2014. U.S. defense officials have
Game-Changing Technology?
stated that the HGV may be capable of performing
Some analysts have asserted that the speed, accuracy, and
“extreme maneuvers” during flight, which would allow it to
maneuverability of hypersonic boost-glide weapons will
evade U.S. ballistic missile defenses. Unclassified reports
fundamentally change the character of warfare. Former
indicate this glider would likely be equipped with
acting Secretary of the Navy Thomas Modly made this case
conventional warheads, and when mated with the DF-17
in January 2020 when he noted that these technologies
booster, could travel to ranges of 1,800-2,500 kilometers.
“have already changed the nature of the battlespace” and
that they “can destabilize the global security environment
China is also developing the DF-41 long-range
and pose an existential threat to our nation.” Others
intercontinental ballistic missile, which former commander
question this assessment. They note that boost-glide
of U.S. Northern Command General Terrence
systems can reach their targets more quickly than other
O’Shaughnessy seemed to confirm could carry a nuclear-
maneuverable systems, like aircraft and subsonic cruise
capable HGV. Reports additionally indicate that China has
missiles. But adversaries armed with ballistic missiles have
tested an HGV on a fractional orbital bombardment system
long been able to attack U.S. forces, allies, and territory,
(FOBS)—a ballistic missile booster that carried the HGV
even without maneuvering warheads. Consequently, they
into orbit before the HGV de-orbited and approached its
argue that there is nothing new about the threat from
target. Experts assert that this type of system might provide
nuclear-armed HGVs, when compared with other nuclear-
China with the ability to launch HGVs over the South Pole,
armed missiles, and nothing existential about a threat from
thus evading U.S. early warning assets that track threats
conventionally armed HGVs.
over the North Pole and further reducing the amount of
warning time prior to a strike.
Crisis Instability?
Some contend that China has prioritized HGV development
Boost-glide systems could accelerate the pace of warfare
to counter “specific security threats from increasingly
and create incentives to strike first in a crisis. If the United
sophisticated U.S. military technology.” This includes both
States and potential adversaries develop these systems to
U.S. hypersonic weapons that could threaten strikes against
strike promptly against high-value targets protected by
China’s nuclear arsenal and supporting infrastructure, and
missile defenses, each side may believe it has to strike first,
U.S. missile defense deployments that could then limit
and strike fast, to achieve its objectives. This dynamic—
China’s ability to conduct a retaliatory strike against the
often referred to as crisis instability—could provoke the
United States. In this framework, nuclear-armed HGVs on
start of a conflict even if neither party to the crisis initially
long-range missiles would ensure that China had the ability
planned to strike first.
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 by developing defensive
HGVs on medium-range missiles would aid China’s efforts
systems to track and engage them. Experts disagree on the
to threaten U.S. assets in the Indo-Pacific region,
cost and technological feasibility of this approach.
particularly when faced with growing U.S. regional missile
Policymakers may also consider mechanisms to ban or limit
defense capabilities.
the deployment of these weapons to avoid the crisis
Arms Race Dynamics?
instabilities created by their short time of flight. On 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
Amy F. Woolf, former Specialist in Nuclear Weapons
argue that the United States is falling behind in this contest
Policy, originally co-authored this report.
because Russia and China have both displayed operational
systems. Others argue that the United States is leading, and
Kelley M. Sayler, Analyst in Advanced Technology and
may be escalating the race because it has accelerated its
Global Security
programs and expanded them to include short-, medium-,
IF11459
and long-range systems.
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Defense Primer: Hypersonic Boost-Glide Weapons
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