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Updated March 22, 2024
Defense Primer: Hypersonic Boost-Glide Weapons
The U.S. Department of Defense (DOD) is pursuing two
detect, track, and defend against an attack. The United
types of hypersonic weapons technologies: boost-glide
States would likely detect the booster’s launch, as it would
systems that place a maneuverable glide vehicle atop a
for the launch of any ballistic missile, but it would not be
ballistic missile or rocket booster, and cruise missiles that
able to predict the HGV’s flight path. In addition, although
would use high-speed, air-breathing engines known as
an HGV launched by a rocket booster would reach its target
scramjets to travel to hypersonic speeds. This In Focus
far more quickly than a warhead delivered by an aircraft or
addresses only the first of these technologies.
subsonic cruise missile (in minutes instead of hours), it
The Pentagon’s FY202
would not travel faster than a ballistic reentry vehicle.
5 budget request for hypersonic
However, it would be more difficult to predict the intended
weapons was $6.9 billion (of a total $9.8 billion request for
target and to direct missile defense interceptors toward the
long-range fires), up from $4.7 billion in FY2023. The
attacking HGV.
Pentagon declined to provide a breakout of funding for
hypersonic weapons in FY2024, but it requested a total of
Hypersonic Boost-Glide Programs
$11 billion for long-range fires. Pentagon officials have
stated that hypersonic weapons could attack priority targets
United States
promptly and with improved accuracy without facing defeat
When the United States began to assess the military utility
by an 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, as
deep into an adversary’s territory to attack defended,
well as about the potential threats to U.S. forces, allies, and
hardened, and time-urgent targets. (For an overview of the
territory.
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.
Woolf.) More recently, the Pentagon has increased funding
Hypersonic glide vehicles (HGVs), like all weapons
and accelerated development programs for shorter and
delivered by medium- and longer-range rocket boosters, can
intermediate-range boost-glide systems that could conduct
travel at speeds of at least Mach 5, or about 1 mile per
prompt attacks against heavily defended targets in regional
second. The key difference between missiles armed with
conflicts. The Navy, Air Force, Army, and DARPA all
HGVs and missiles armed with ballistic reentry vehicles
maintain hypersonic weapons programs. (Details on these
(i.e., those that travel on a ballistic trajectory throughout
programs can be found in CRS Report R45811, Hypersonic
their flight) is not their speed, but their ability to maneuver
Weapons: Background and Issues for Congress, by Kelley
and change course after they are released from their rocket
M. Sayler.)
boosters. In addition, although it is not necessary, many
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
Chinese and Russian systems.
Figure 1. Flight Trajectory of Ballistic Missiles vs.
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
missiles equipped with Avangard.
Source: CRS image based on an image in “Gliding missiles that fly
faster than Mach 5 are coming,” The Economist, April 6, 2019.
Russia views the Avangard system as a part of its nuclear
retaliatory capability, ensuring that Russian missiles could
Taken together, the HGV’s novel trajectory and
penetrate U.S. ballistic missile defenses. According to the
maneuverability in flight would complicate a U.S. effort to
Pentagon’s 2022 Missile Defense Review, the United States
https://crsreports.congress.gov
Defense Primer: Hypersonic Boost-Glide Weapons
relies on nuclear deterrence, not ballistic missile defenses,
When asked about this dynamic in February 2020, Admiral
to counter Russia’s long-range missile forces. Nevertheless,
Charles Richard, the commander of U.S. Strategic
in March 2018, President Putin stated that Russia had
Command, noted that there “is a competition, just like any
pursued HGV technologies in response to the U.S. 2002
other military competition.” But he did not characterize it as
withdrawal from the 1972 Anti-ballistic Missile Treaty.
an arms race. He noted that the United States was
Some U.S. analysts have noted, however, that Russia could
developing technologies needed to meet U.S. national
use the Avangard as part of a first strike, even in the
objectives and that he expected the United States to be
absence of U.S. ballistic missile defenses, to attack critical
successful in meeting its security goals. Others have noted
targets quickly. Others have assessed that Russia is likely to
that the same is true for Russia and China; each is
deploy Avangard in small numbers, so it will add little to
developing HGVs to meet its own security interests, not to
Russia’s existing nuclear force structure.
counter or match the U.S. development of HGVs.
China
Specifically, both seem to be responding to concerns about
U.S. ballistic missile defense programs.
China has developed an HGV known as the DF-ZF
(previously referred to as the WU-14) and has tested it at
Game-Changing Technology?
least nine times since 2014. U.S. defense officials have
Some analysts have asserted that the speed, accuracy, and
stated that the HGV may be capable of performing
maneuverability of hypersonic boost-glide weapons will
“extreme maneuvers” during flight, which would allow it to
fundamentally change the character of warfare. Former
evade U.S. ballistic missile defenses. Unclassified reports
acting Secretary of the Navy Thomas Modly made this case
indicate this glider would likely be equipped with
in January 2020 when he noted that these technologies
conventional warheads, and when mated with the DF-17
“have already changed the nature of the battlespace” and
booster, could travel to ranges of 1,800-2,500 kilometers.
that they “can destabilize the global security environment
and pose an existential threat to our nation.” Others
China is also developing the DF-41 long-range
question this assessment. They note that boost-glide
intercontinental ballistic missile, which former commander
systems can reach their targets more quickly than other
of U.S. Northern Command General Terrence
maneuverable systems, like aircraft and subsonic cruise
O’Shaughnessy seemed to confirm could carry a nuclear-
missiles. But adversaries armed with ballistic missiles have
capable HGV. Reports additionally indicate that China has
long been able to attack U.S. forces, allies, and territory,
tested an HGV on a fractional orbital bombardment system
even without maneuvering warheads. Consequently, they
(FOBS)—a ballistic missile booster that carried the HGV
argue that there is nothing new about the threat from
into orbit before the HGV de-orbited and approached its
nuclear-armed HGVs, when compared with other nuclear-
target. Experts assert that this type of system might provide
armed missiles, and nothing existential about a threat from
China with the ability to launch HGVs over the South Pole,
conventionally armed HGVs.
thus evading U.S. early warning assets that track threats
over the North Pole and further reducing the amount of
Crisis Instability?
warning time prior to a strike.
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
DOD is seeking to address the potential threats posed by
to retaliate after a U.S. attack, even if the United States
hypersonic boost-glide weapons by developing defensive
were to expand its ballistic missile defense capabilities.
systems to track and engage them. Experts disagree on the
HGVs on medium-range missiles would aid China’s efforts
cost and technological feasibility of this approach.
to threaten U.S. assets in the Indo-Pacific region,
Policymakers may also consider mechanisms to ban or limit
particularly when faced with growing U.S. regional missile
the deployment of these weapons to avoid the crisis
defense capabilities.
instabilities created by their short time of flight. On the
Arms Race Dynamics?
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
Amy F. Woolf, former Specialist in Nuclear Weapons
be competing to be the first to deploy these systems. Some
Policy, originally coauthored this In Focus.
argue that the United States is falling behind in this contest
because Russia and China have both displayed operational
Kelley M. Sayler, Specialist in Advanced Technology and
systems. Others argue that the United States is leading, and
Global Security
may be escalating the race because it has accelerated its
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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