Defense Primer: Ballistic Missile Defense
Updated January 30, 2024
Defense Primer: Ballistic Missile Defense
The United States has been developing and deploying
North Korea likely has an arsenal of hundreds of SRBMs
ballistic missile defenses (BMD) to defend against enemy
that can reach all of South Korea and perhaps dozens of
missiles continuously since the late 1940s. In the late 1960s
MRBMs (whose reliability at this point remains uncertain),
and early 1970s, the United States deployed a limited
capable of reaching Japan and U.S. bases in the region.
nuclear-tipped BMD system to protect a portion of its U.S.
North Korea has flight-tested two types of road-mobile
land-based nuclear ICBM (intercontinental ballistic missile)
ICBMs that have the range to strike the U.S. homeland. The
force in order to preserve a strategic deterrent against a
Defense Intelligence Agency (DIA) has assessed that
Soviet nuclear attack on the Homeland. That system
“North Korea’s continued development of ICBMs, IRBMs,
became active in 1975 but shut down in 1976 because of
and [submarine-launched ballistic missiles] demonstrates its
concerns over cost and effectiveness. In the FY1975
intention to bolster its nuclear delivery capability.”
budget, the Army began funding research into hit-to-kill or
kinetic energy interceptors as an alternative—the type of
The intelligence community assesses that Iran has the
interceptor technology that dominates U.S. BMD systems
largest inventory of ballistic missiles in the Middle East.
today.
Those missiles are armed with conventional warheads; Iran
does not have a nuclear weapons capability. Most of Iran’s
In 1983, President Reagan announced an enhanced effort
ballistic missile force consists of SRBMs with ranges less
for BMD. Since the start of the Reagan initiative in 1985,
than 500 km, which it views as a tactical warfighting force.
BMD has been a key national security interest in Congress,
Iran also has a growing and significant number of MRBMs
which has appropriated well over $200 billion for a broad
capable of striking targets throughout the region, which it
range of BMD research and development programs and
views as a deterrent force. Iran does not appear to have a
deployment of BMD systems here and abroad.
dedicated ICBM program.
The Missile Defense Agency (MDA) is charged with the
Almost all of China’s SRBMs are deployed at bases
mission to develop, test, and field an integrated, layered,
opposite Taiwan. China’s MRBMs can reach U.S. bases, as
BMD system (BMDS) to defend the United States, U.S.
well as U.S. allies and partners in the region. China’s
deployed forces, and U.S. allies and partners against
missile forces could also target U.S. naval ships in
ballistic missiles of all ranges and in all phases of flight.
Northeast Asia. Additionally, China is working on a range
The FY2024 budget request is $28.9 billion for overall
of technologies to attempt to counter U.S. and other
missile defeat and defense, including $9.2 billion for
countries’ BMD systems. China’s ICBM and some nuclear-
BMDS.
armed MRBM forces are intended for strategic and regional
deterrence.
Ballistic Missile Threats
After an initial powered phase of flight, a ballistic missile
The Major Elements of the U.S. BMDS
leaves the atmosphere and follows an unpowered trajectory
The United States has deployed a global array of networked
or flight path before reentering the atmosphere toward a
ground, sea, and space-based sensors for target detection
predetermined target. Ballistic missiles have an effective
and tracking, an extensive number of ground- and sea-based
range from a few hundred kilometers (km) to more than
hit-to-kill (direct impact) and blast fragmentation warhead
10,000 km. Short-range ballistic missiles (SRBMs) range
interceptors, and a global network of command, control,
from 300-1,000 km and are generally considered for tactical
and battle management capabilities to link those sensors
military use. Medium-range ballistic missiles (MRBMs)
with those interceptors.
have a range from 1,000-5,500 km, although most are
armed with conventional warheads and range less than
Ground-Based Midcourse Defense (GMD)
3,500 km. ICBMs range further than 5,500 km and are
Since 2004, the United States has deployed a force of 44
generally considered as strategic deterrent forces.
Ground-based Interceptors (GBI) at Fort Greely, AK, and
Vandenberg Air Force Base, CA. The GMD system is
Most of the world’s ballistic missiles belong to the United
designed to destroy a limited attack in space from ICBMs
States and its allies and partners; however, China and, in
aimed at the United States, to include from North Korea
particular, Russia also have significant numbers of ICBMs.
and Iran. Although the GMD system has been praised by
Russia continues to possess intermediate-range ballistic and
senior military leaders, it does have a somewhat mixed
cruise missiles (3,500-5,500 km), which led to the U.S.
flight test record, having failed 8 out of 18 intercept
withdrawal from the 1987 Intermediate Nuclear Forces
attempts between 1999 and 2018.
(INF) Treaty. The 2022 Missile Defense Review
additionally identifies ballistic missile threats from North
Terminal High Altitude Area Defense (THAAD)
Korea and Iran.
THAAD is a highly mobile, rapidly deployable BMD
system designed to shoot down incoming short- and
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Defense Primer: Ballistic Missile Defense
medium-range missiles during their final or terminal phase
Other Regional BMD Cooperative Efforts
of flight. It is designed to provide broad area coverage
Similar to the EPAA, the United States has sought since
against threats to population centers and industrial
2010 to formalize a regional cooperative BMD capability
resources as well as military forces.
both in Northeast Asia (with Japan, Korea, and Australia)
and in the Persian Gulf. Although many of the BMD
THAAD was initially proposed in 1987 and its first flight
elements of a potential cooperative system are in place in
test occurred in April 1995. It had a very poor test record—
these regions, wariness between likely foreign partners and
failing its first six flight tests—until the first successful
opposition from countries such as China have prevented a
intercept in 1999, following the program’s restructuring. In
formal agreement and participation from going forward.
recent years, THAAD’s test record has demonstrated high
effectiveness and reliability, succeeding in 15 out of 15
Cooperation with Israel
intercept attempts between 1999 and 2018. Many now
The United States signed a memorandum of understanding
consider it the most advanced BMD system in the world.
with Israel on the development of missile defense systems
The United States has delivered seven THAAD batteries to
on May 6, 1985. Since then, the United States has invested
the U.S. Army. U.S. THAAD batteries are now deployed in
significantly in Israel’s missile defense programs and
Guam, South Korea, and the Persian Gulf. THAAD radars
systems, including Iron Dome (designed to intercept short-
are exceptionally powerful and are currently deployed in
range rockets), David’s Sling (designed to intercept short-
Turkey, Israel, and Japan. Any future THAAD batteries
to medium- and medium- to long-range missiles), and
produced will be for Foreign Military Sales.
Arrow (designed to intercept medium- to long-range
missiles)—the latter two of which were jointly developed.
Aegis BMD
MDA requested $500 million in FY2024 to support
The Aegis BMD program gives Navy Aegis cruisers and
cooperative missile defense with Israel.
destroyers a capability for providing regional defense
against short- and medium-range ballistic missile attacks.
Legislative Issues
Under the FY2024 budget submission, the number of
BMD has broad support across the political spectrum and
BMD-capable Navy Aegis ships is projected to increase to
within the military as evidenced by the high degree of
56—from 43—by the end of FY2025. Aegis BMD ships
funding support for the program regardless of which party
and Aegis Ashore (land-based) capabilities in Romania and
controls the White House and Congress, especially since
Poland contribute to NATO’s territorial defense mission.
the early 2000s.
Aegis BMD succeeded in 40 out of 49 intercept attempts
between 1999 and 2018.
Congress has historically cut ballistic missile defense
programs in one of three circumstances: (1) cases in which
Patriot Advanced Capability-3 (PAC-3)
program delays allow for opportunistic program cuts, (2)
The Army Patriot system is the most mature element of the
cases in which there is long-lead procurement of
BMDS. It was used in combat in the 1991 and 2003 Iraq
components that have demonstrated questionable test
wars and is fielded around the world by the United States
results, and (3) cases in which the program is not likely to
and many others that have purchased the system. Patriot is a
be fielded in the short- or medium-term due to technical
mobile, transportable system designed to defend areas such
constraints.
as military bases and air fields from advanced aircraft,
CRS Products
cruise missiles, and tactical ballistic missiles. Patriot works
CRS In Focus IF10472, North Korea’s Nuclear Weapons and
with THAAD to provide an integrated and overlapping
Missile Programs, by Mary Beth D. Nikitin and Samuel D.
defense against attacking missiles in their final phase of
Ryder.
flight.
CRS Report R42849, Iran’s Ballistic Missile and Space Launch
Foreign BMD Participation
Programs, by Steven A. Hildreth.
CRS Report RL33745, Navy Aegis Ballistic Missile Defense (BMD)
The United States has missile defense cooperative programs
Program: Background and Issues for Congress, by Ronald
with multiple allies. MDA actively participates in NATO
O'Rourke.
activities to develop an integrated NATO BMD capability.
Patriot systems have been purchased by allies, acquisition
Other Resources
of THAAD is in various stages of contract negotiation and
Defense Department. 2022 Missile Defense Review. October
acquisition, and countries such as Japan have acquired
2022.
Aegis BMD capabilities. The Kingdom of Saudi Arabia is
on contract to receive seven THAAD batteries.
This In Focus was originally authored by Stephen M.
European Phased Adaptive Approach (EPAA)
McCall, former Analyst in Military Space, Missile Defense,
At the 2010 Lisbon Summit, NATO agreed to develop a
and Defense Innovation.
missile defense capability to protect European NATO
populations, territory, and forces against the threats posed
Kelley M. Sayler, Coordinator, Analyst in Advanced
by the proliferation of ballistic missiles. The U.S.
Technology and Global Security
contribution to that NATO effort is the EPAA, which
IF10541
includes the deployment of a THAAD radar in Turkey,
Aegis BMD ships in the Mediterranean Sea, and Aegis
Ashore in Romania and Poland.
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Defense Primer: Ballistic Missile Defense
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