Updated October 9, 2019
Defense Primer: Ballistic Missile Defense
The United States has been developing and deploying
ballistic missile defenses (BMD) to defend against enemy
missiles continuously since the late 1940s. In the late 1960s
and early 1970s, the United States deployed a limited
nuclear-tipped BMD system to protect a portion of its U.S.
land-based nuclear ICBM (intercontinental ballistic missile)
force in order to preserve a strategic deterrent against a
Soviet nuclear attack on the Homeland. That system
became active in 1975 but shut down in 1976 because of
concerns over cost and effectiveness. In the FY1975
budget, the Army began funding research into hit-to-kill or
kinetic energy interceptors as an alternative—the type of
interceptor technology dominates U.S. BMD systems today.
In 1983, President Reagan announced an enhanced effort
for BMD. Since the start of the Reagan initiative in 1985,
BMD has been a key national security interest in Congress.
It has appropriated well over $200 billion for a broad range
of research and development programs and deployment of
BMD systems here and abroad.
North Korea likely has an arsenal of hundreds of SRBMs
that can reach all of South Korea and perhaps dozens of
MRBMs (whose reliability at this point remains uncertain),
capable of reaching Japan and U.S. bases in the region.
North Korea is in the process of developing an ICBM
capability that could strike the U.S. homeland with a
nuclear warhead. Although North Korea has conducted a
number of nuclear tests, it is unclear whether any of their
ballistic missiles are armed with a nuclear warhead.
The IC assesses that Iran has the largest inventory of
ballistic missiles in the Middle East. Those missiles are
armed with conventional warheads; Iran does not have a
nuclear weapons capability. Most of Iran’s ballistic missile
force consists of SRBMs with ranges less than 500 km,
which it views as a tactical warfighting force. Iran also has
a growing and significant number of MRBMs capable of
striking targets throughout the region, which it views as a
deterrent force. Iran does not appear to have a dedicated
The Missile Defense Agency (MDA) is charged with the
mission to develop, test, and field an integrated, layered,
BMD system (BMDS) to defend the United States, its
deployed forces, allies, and friends against all ranges of
enemy hypersonic and ballistic missiles in all phases of
flight. Current U.S. policy, however, is not directed at the
strategic nuclear deterrent forces of Russia and China. The
FY2020 budget request is $13.6 billion for missile defense,
$9.4 billion of which is for MDA.
Almost all of China’s SRBMs are deployed at bases
opposite Taiwan. China’s MRBMs can reach U.S. bases, as
well as U.S. friends and allies in the region. China’s missile
forces could also target U.S. naval ships in Northeast Asia.
Additionally, China is working on a range of technologies
to attempt to counter U.S. and other countries’ BMD
systems. China’s ICBM and some nuclear-armed MRBM
forces are intended for strategic and regional deterrence.
Ballistic Missile Threats
The United States has deployed a global array of networked
ground, sea, and space-based sensors for target detection
and tracking, an extensive number of ground- and sea-based
hit-to-kill (direct impact) and blast fragmentation warhead
interceptors, and a global network of command, control,
and battle management capabilities to link those sensors
with those interceptors.
After an initial powered phase of flight, a ballistic missile
leaves the atmosphere and follows an unpowered trajectory
or flight path before reentering the atmosphere toward a
predetermined target. Ballistic missiles have an effective
range from a few hundred kilometers to more than 10,000
kilometers (km). Short-range ballistic missiles (SRBMs)
range from 300-1,000 km and are generally considered for
tactical military use. Medium-range ballistic missiles
(MRBMs) have a range from 1,000-5,500 km, although
most are armed with conventional warheads and range less
than 3,500 km. ICBMs range further than 5,500 km and are
generally considered as strategic deterrent forces.
Most of the world’s ballistic missiles belong to the United
States and its friends and allies. Russia, especially, and
China have significant numbers of ICBMs. Russia
continues to possess intermediate-range ballistic cruise
missiles (3,500-5,500 km), which led to the U.S.
withdrawal from the 1987 INF (Intermediate Nuclear
Forces) Treaty. The ballistic missile threats of most concern
to the United States today are primarily the SRBM and
MRBM forces from North Korea, Iran and China, and
growing North Korean ICBM capabilities.
The Major Elements of the U.S. BMDS
Ground-based Midcourse Defense (GMD)
Since 2004, the United States has deployed a force of 44
(expanding now to 64) Ground-based Interceptors (GBI) at
Ft, Greely, Alaska and Vandenberg Air Force Base,
California. The GMD system is designed to destroy a
limited attack in space from ICBMs aimed at the United
States, to include from North Korea and even Iran.
Although the GMD system is praised by senior military
leaders and is generally viewed in successful terms, it does
have a somewhat mixed flight test record.
Terminal High Altitude Area Defense (THAAD)
THAAD is a highly mobile, rapidly deployable BMD
system designed to shoot down attacking short- and
medium-range missiles during their final or terminal phase
of flight. It is designed to provide broad area coverage
Defense Primer: Ballistic Missile Defense
against threats to population centers and industrial
resources as well as military forces.
THAAD was initially proposed in 1987 and its first flight
test occurred in April 1995. It had a very poor test record
until the first successful intercept in 1999. In recent years,
THAAD’s test record has demonstrated high effectiveness
and reliability. Many now consider it the most advanced
BMD system in the world. The United States has delivered
seven THAAD batteries to the U.S. Army. U.S. THAAD
batteries are now deployed in Guam, South Korea, and the
Persian Gulf. THAAD radars are exceptionally powerful
and are currently deployed in Turkey, Israel, and Japan.
Any future THAAD batteries produced will be for Foreign
The Aegis BMD program gives Navy Aegis cruisers and
destroyers a capability for providing regional defense
against short- and medium-range ballistic missile attacks.
Under the FY2020 budget submission, the number of
BMD-capable Navy Aegis ships is projected to increase
from 38 to 59 at the end of FY2024. Aegis BMD ships and
Aegis Ashore (land-based) capabilities in Romania (and
Poland by 2020) contribute to NATO’s territorial defense
mission. Testing results have shown significant Aegis BMD
Patriot Advanced Capability-3 (PAC-3)
The Army Patriot system is the most mature element of the
BMDS. It was used in combat in the 1991 and 2003 Iraq
wars and is fielded around the world by the United States
and many others that have purchased the system. Patriot is a
mobile, transportable system designed to defend areas such
as military bases and air fields. Patriot works with THAAD
to provide an integrated and overlapping defense against
attacking missiles in their final phase of flight.
Foreign BMD Participation
Other Regional BMD Cooperative Efforts
Similar to the EPAA, the United States has sought since
2010 to formalize a regional cooperative BMD capability
both in Northeast Asia (with Japan, Korea and Australia)
and in the Persian Gulf. Although many of the BMD
elements of a potential cooperative system are in place in
these regions, wariness between likely foreign partners and
opposition from countries such as China have prevented a
formal agreement and participation from going forward.
Cooperation with Israel
Since 1986, the United States has invested significantly in
Israel’s missile defense programs and systems designed to
protect against missile and rocket attacks. The United States
also provided a THAAD radar to Israel in 2008.Thus far,
the United States has provided about $2.5 billion for Israeli
programs, which include the Arrow systems designed to
counter short- and medium-range ballistic missiles, Iron
Dome (to counter short-range rockets), and David’s Sling
(designed to counter longer range rockets).
BMD has broad support across the political spectrum and
within the military as evidenced by the high degree of
funding support for the program regardless of which party
controls the White House and Congress, especially since
the early 2000s.
Where Congress has cut programs tends to fall in three
areas: where program delays allow for opportunistic
program cuts, cuts for long-lead procurement of
components with still questionable test results, and newer
programs not likely to come to fruition in the short or
medium term. Congress has also thus far been unwilling to
fund programs that might lead to emplacing interceptor
capabilities in space. But this reticence may now be
changing as the geopolitical and space domain is changing.
The United States has missile defense cooperative programs
with multiple allies. MDA actively participates in NATO
activities to develop an integrated NATO BMD capability.
Patriot systems have been purchased by allies, acquisition
of THAAD is in various stages of contract negotiation and
acquisition, and countries such as Japan have acquired
Aegis BMD capabilities. The Kingdom of Saudi Arabia
(KSA) is on contract to receive seven THAAD batteries.
European Phased Adaptive Approach (EPAA)
At the 2010 Lisbon Summit, NATO agreed to develop a
missile defense capability to protect NATO European
populations, territory and forces against the threats posed
by the proliferation of ballistic missiles. The U.S.
contribution to that NATO effort is the EPAA, which
includes the deployment of a THAAD radar in Turkey, the
deployment of Aegis BMD ships in Europe, and the
deployment of an Aegis Ashore in Romania. A second
Aegis Ashore capability is being constructed in Poland,
which will complete the U.S. commitment to NATO’s
P.L. 106-38 – National Missile Defense Act of 1999.
CRS In Focus IF10472, North Korea’s Nuclear and Ballistic
Missile Programs, by Steven A. Hildreth and Mary Beth D.
CRS Report R42849, Iran’s Ballistic Missile and Space Launch
Programs, by Steven A. Hildreth
CRS Report RL33745, Navy Aegis Ballistic Missile Defense (BMD)
Program: Background and Issues for Congress, by Ronald
CRS Report R43116, Ballistic Missile Defense in the Asia-Pacific
Region: Cooperation and Opposition, by Ian E. Rinehart, Steven
A. Hildreth, and Susan V. Lawrence
DOD. 2019 Missile Defense Review. Jan. 2019.
Stephen M. McCall, Analyst in Military Space, Missile
Defense, and Defense Innovation
Defense Primer: Ballistic Missile Defense
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