GAO-23-106717 Directed Energy Weapons
Science, Technology Assessment,
and Analytics
MAY 2023
WHY THIS MATTERS
There is a surge in interest in directed energy weapons
from several nations—including the U.S.—primarily for
counter drone missions. These weapons use
electromagnetic energy to cause effects ranging from
deterrence to destruction. They offer capabilities that
conventional weapons may not, but challenges have so
far prevented widespread operational use.
SCIENCE & TECH SPOTLIGHT:
DIRECTED ENERGY
WEAPONS
/// THE TECHNOLOGY
What is it? Directed energy weapons (DEW) use concentrated
electromagnetic energy to combat enemy forces and assets. These
weapons include high energy lasers and other high power
electromagnetics—such as millimeter wave and high power microwave
weapons. Unlike weapons that fire bullets or missiles, DEWs can respond
to a threat in different ways. For example, they can temporarily degrade
electronics on a drone or physically destroy it. See our 2022 Spotlight for
more information on counter-drone technology.
How does it work? Each type of DEW uses a different region of the
electromagnetic spectrum (see fig. 1). This spectrum describes all of the
kinds of light—including those the human eye cannot see—and classifies
them according to wavelength. Different types of electromagnetic energy
have different properties. For example, the wavelength affects what the
directed energy can penetrate—such as metal or human skin.
Figure 1. Location of directed energy weapons on the electromagnetic spectrum.
All DEWs emit energy at the speed of light, and are often discussed in
terms of their power output—the amount of electromagnetic energy
transferred over time. While DEWs use electromagnetic energy similar to
everyday items, such as household microwaves, their power output is
vastly higher, as described below.
High energy lasers produce a very narrow beam of light, usually in the
infrared to visible region, and are typically used on one target at a time.
The beam can be pulsed or continuous, generating a power output of at
least 1 kilowatt. This output is 200,000 times greater than a typical laser
pointer and is capable of melting steel.
Millimeter wave weapons have wavelengths between 1 and 10
millimeters and generate more than 1 kilowatt of power. Millimeter wave
weapons have a larger beam size than high energy lasers and therefore
can affect multiple targets at once.
High power microwave weapons produce microwaves, which have
longer wavelengths than high energy lasers and millimeter wave
weapons. These weapons can produce more than 100 megawatts of
power, which is nearly 150,000 times more powerful than the average
household microwave. Like millimeter wave weapons, they can also affect
multiple targets because of their larger beam size.
Each DEW can produce a range of effects from nonlethal to lethal,
depending on factors such as the time on target, the distance to the
target, and even the part of the target on which the DEW is focused.
DEWs can use this range of effects to graduate responses to a threat. A
graduated response could start with temporarily preventing use of an
asset or its access to an area and increase to destruction of the asset if
necessary (see fig. 2).
Figure 2. Examples of graduated responses using directed energy weapons.
DEWs can deny entrance to an area or prevent enemy forces or assets
from functioning within an area. DEWs used for denial do not cause long-
term damage to targets, and when enemy forces or assets leave the area,
they typically regain function or the effect is mitigated. For example, the
Department of Defense’s (DOD) Active Denial System uses millimeter
waves that interact with the water and fat molecules in a person’s skin to
create a heating sensation. During testing, the discomfort persuaded
individuals to move away from the area.
DEWs can also degrade the efficacy of an enemy’s assets. For example,
high energy lasers can temporarily overwhelm a person or a sensor’s
ability to see or sense by emitting a glare—called dazzling. Dazzling can
act as a non-verbal warning before resorting to increased force.
Science, Technology Assessment,
and Analytics
GAO-23-106717 Directed Energy Weapons
If a greater amount of force is required, DEWs can also damage or
destroy enemy assets. To do this, a high energy laser can emit
electromagnetic energy with a wavelength the target material absorbs
most effectively, melting the material. The laser could focus on a sensor
and damage a drone, or focus on a fuel tank or battery and destroy it.
How mature is it? DEWs range in maturity from research projects to
prototypes tested in the field. DOD named DEWs as a technology critical
to enabling the 2018 National Defense Strategy and reported spending
about $1 billion annually for the last 3 years on research and
development. The U.S. military has tested a variety of DEW prototypes
since 2014, primarily for counter-drone missions. For example, the Air
Force’s prototype Tactical High Power Microwave Operational Responder
(THOR) recently completed 2 years of testing. DOD is researching ways
to increase the power output of DEWs to engage more powerful targets—
like missiles. However, as GAO recently reported, the U.S. military faces
challenges bridging the gap between DEW development and acquisition,
potentially limiting widespread operational use.
Why now? DEW research and development has been ongoing for
decades in many countries—including the U.S.—and is currently
experiencing a surge worldwide. This surge stems in part from advances
in technology and a desire to maintain competitiveness on the battlefield.
Technological innovations, such as the development of smaller lasers that
are safer to operate, enable modern DEWs to be much more portable and
practical. For example, a four-wheel all-terrain vehicle can now hold a
high energy laser powerful enough to damage drones. The U.S. and 30
other nations are developing DEWs, most for counter-drone missions,
according to a 2021 Air Force report.
/// OPPORTUNITIES
Complement to conventional weapons. DEWs use energy fired
at the speed of light, making them faster and potentially less costly
per shot than missiles. Some DEWs have virtually unlimited
ammunition and can fire as long as they have power.
Ease of graduated response. DOD can tailor DEWs to meet
mission needs from nonlethal to lethal responses. For example, the
longer a laser is focused on target, the more damage or destruction
will occur.
Advancing other uses. Research and development for DEWs
could also benefit civilian uses. For example, the development of
higher energy lasers could help projects that use directed energy to
transport or “beam” power to remote and disadvantaged locations.
/// CHALLENGES
Technological limitations. DEWs are generally less effective the
farther they are from the target, and atmospheric conditions and
cooling requirements can limit their effectiveness. For example, fog
and storms can reduce laser beam range and quality.
Battlefield use. Decisions about how and when to use DEWs or
conventional weapons may be challenging. For example, wider
beam DEWs, such as high power microwave or millimeter wave
weapons, affect all assets in an area, whether friend or foe.
Ethical and health concerns. Although there are potentially
relevant international laws and guidelines, their applicability to
DEWs is not always well defined. Uncertainty around long-term
health effects of DEWs on people either intentionally or
unintentionally exposed to directed energy has led to concerns
regarding the ethics of using DEWs.
/// POLICY CONTEXT AND QUESTIONS
As the technology matures, what actions could policymakers take
to help bridge the gap between DEW development and
acquisition?
What actions could policymakers take to ensure there is
appropriate guidance for using DEWs as the technology matures?
What are the trade-offs of using nonlethal DEW technologies
before potential health effects are fully understood?
/// SELECTED GAO WORK
Directed Energy Weapons: DOD Should Focus on Transition Planning,
GAO-23-105868.
Science & Tech Spotlight: Counter-Drone Technologies, GAO-22-105705.
Electromagnetic Spectrum Operations: DOD Needs to Address
Governance and Oversight Issues to Help Ensure Superiority,
GAO-21-64.
/// SELECTED REFERENCES
Air Force Research Laboratory, Directed Energy Futures 2060: 2021.
Congressional Research Service, Department of Defense Directed Energy Weapons:
Background and Issues for Congress,
R46925 (Washington, D.C.: 2022).
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