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Updated May 5, 2022
Defense Primer: Hypersonic Boost-Glide Weapons
The U.S. Department of Defense (DOD) is pursuing two
States would likely detect the booster’s launch, as it would
types of hypersonic weapons technologies: boost-glide
for the launch of any ballistic missile, but it would not be
systems that place a maneuverable glide vehicle atop a
able to predict the HGV’s flight path. In addition, although
ballistic missile or rocket booster, and cruise missiles that
an HGV launched by a rocket booster would reach its target
would use high-speed, air-breathing engines known as
far more quickly than a warhead delivered by an aircraft or
scramjets to travel to hypersonic speeds. This In Focus
subsonic cruise missile (in minutes instead of hours), it
addresses only the first of these technologies.
would not travel faster than a ballistic reentry vehicle.
However, it would be more difficult to predict the intended
The Pentagon’s FY2023 budget request for hypersonic-
target and to direct missile defense interceptors toward the
related research is $4.7 billion—up from $3.8 billion in the
attacking HGV.
FY2022 request. This increased funding and statements
from Pentagon officials demonstrate growing support for
Hypersonic Boost-Glide Programs
weapons that could attack priority targets promptly and
with improved accuracy without facing defeat by an
United States
adversary’s air or missile defense systems. Pentagon
When the United States began to assess the military utility
officials have also expressed concerns about advances in
of hypersonic boost-glide weapons in the early 2000s, it
hypersonic weapons technologies in Russia and China, and
sought to develop longer-range systems that could reach
on the potential threats to U.S. forces, allies, and territory.
deep into an adversary’s territory to attack defended,
hardened, and time-urgent targets. (For an overview of the
Characteristics of Hypersonic
history of U.S. programs, see CRS Report R41464,
Glide Vehicles
Conventional Prompt Global Strike and Long-Range
Hypersonic glide vehicles (HGVs), like all weapons
Ballistic Missiles: Background and Issues, by Amy F.
delivered by medium- and longer-range rocket boosters, can
Woolf.) More recently, the Pentagon has increased funding
travel at speeds of at least Mach 5, or about 1 mile per
and accelerated development programs for shorter and
second. The key difference between missiles armed with
intermediate-range boost-glide systems that could conduct
HGVs and missiles armed with ballistic reentry vehicles
prompt attacks against heavily defended targets in regional
(i.e., those that travel on a ballistic trajectory throughout
conflicts. The Navy, Air Force, Army, and DARPA all
their flight) is not their speed, but their ability to maneuver
maintain hypersonic weapons programs. (Details on these
and change course after they are released from their rocket
programs can be found in CRS Report R45811, Hypersonic
boosters. In addition, although it is not necessary, many
Weapons: Background and Issues for Congress, by Kelley
concepts for the delivery of HGVs presume that the
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: CRS image based on an image in “Gliding missiles that fly
of Avangard in 2016 and 2018. On December 27, 2019, the
faster than Mach 5 are coming,” The Economist, April 6, 2019.
Russian military announced that it had activated two SS-19
missiles equipped with Avangard.
Taken together, the HGV’s novel trajectory and
maneuverability in flight would complicate a U.S. effort to
Russia views the Avangard system as a part of its nuclear
detect, track, and defend against an attack. The United
retaliatory capability, ensuring that Russian missiles could
https://crsreports.congress.gov
Defense Primer: Hypersonic Boost-Glide Weapons
penetrate U.S. ballistic missile defenses. According to the
may be escalating the race because it has accelerated its
Pentagon’s 2019 Missile Defense Review, the United States
programs and expanded them to include short-, medium-,
relies on nuclear deterrence, not ballistic missile defenses,
and long-range systems.
to counter Russia’s long-range missile forces. Nevertheless,
in March 2018, President Putin stated that Russia had
When asked about this dynamic in February 2020, Admiral
pursued HGV technologies in response to the U.S. 2002
Charles Richard, the commander of U.S. Strategic
withdrawal from the 1972 Anti-ballistic Missile Treaty.
Command, noted that there “is a competition, just like any
Some U.S. analysts have noted, however, that Russia could
other military competition.” But he did not characterize it as
use the Avangard as part of a first strike, even in the
an arms race. He noted that the United States was
absence of U.S. ballistic missile defenses, to attack critical
developing technologies needed to meet U.S. national
targets quickly. Others have assessed that Russia is likely to
objectives, and he noted that he expected the United States
deploy Avangard in small numbers, so it will add little to
to be successful in meeting its security goals. Others have
Russia’s existing nuclear force structure.
noted that the same is true for Russia and China; each is
developing HGVs to meet its own security interests, not to
China
counter or match the U.S. development of HGVs.
China has developed an HGV known as the DF-ZF
Specifically, both seem to be responding to concerns about
(previously referred to as the WU-14) and has tested it at
U.S. ballistic missile defense programs.
least nine times since 2014. U.S. defense officials have
stated that the HGV may be capable of performing
Game-Changing Technology?
“extreme maneuvers” during flight, which would allow it to
Some analysts have asserted that the speed, accuracy, and
evade U.S. ballistic missile defenses. Unclassified reports
maneuverability of hypersonic boost-glide weapons will
indicate this glider would likely be equipped with
fundamentally change the character of warfare. Former
conventional warheads, and when mated with the DF-17
acting Secretary of the Navy Thomas Modly made this case
booster, could travel to ranges of 1,800-2,500 kilometers.
in January 2020 when he noted that these technologies
“have already changed the nature of the battlespace” and
China is also developing the DF-41 long-range
that they “can destabilize the global security environment
intercontinental ballistic missile, which former commander
and pose an existential threat to our nation.” Others
of U.S. Northern Command General Terrence
question this assessment. They note that boost-glide
O’Shaughnessy seemed to confirm could carry a nuclear-
systems can reach their targets more quickly than other
capable HGV. Reports additionally indicate that China has
maneuverable systems, like aircraft and subsonic cruise
tested an HGV on a fractional orbital bombardment system
missiles. But adversaries armed with ballistic missiles have
(FOBS)—a ballistic missile booster that carried the HGV
long been able to attack U.S. forces, allies, and territory,
into orbit before the HGV de-orbited and approached its
even without maneuvering warheads. Consequently, they
target. Experts assert that this type of system might provide
argue that there is nothing new about the threat from
China with the ability to launch HGVs over the South Pole,
nuclear-armed HGVs, when compared with other nuclear-
thus evading U.S. early warning assets that track threats
armed missiles, and nothing existential about a threat from
over the North Pole and further reducing the amount of
conventionally armed HGVs.
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
were to expand its ballistic missile defense capabilities.
DOD is seeking to address the potential threats posed by
HGVs on medium-range missiles would aid China’s efforts
hypersonic boost-glide weapons by developing defensive
to threaten U.S. assets in the Indo-Pacific region,
systems to track and engage them. Experts disagree on the
particularly when faced with growing U.S. regional missile
cost and technological feasibility of this approach.
defense capabilities.
Policymakers may also consider mechanisms to ban or limit
the deployment of these weapons to avoid the crisis
Arms Race Dynamics?
instabilities created by their short time of flight. On the
Many analysts have characterized the ongoing U.S.,
other hand, nations might be unwilling to agree to limit
Russian, and Chinese development of HGVs and boost-
these weapons without corresponding limits on missile and
glide weapons as an arms race because each nation seems to
air defenses.
be competing to be the first to deploy these systems. Some
argue that the United States is falling behind in this contest
Kelley M. Sayler, Analyst in Advanced Technology and
because Russia and China have both displayed operational
Global Security
systems. Others argue that the United States is leading, and
Amy F. Woolf, Specialist in Nuclear Weapons Policy
https://crsreports.congress.gov
Defense Primer: Hypersonic Boost-Glide Weapons
IF11459
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