https://crsreports.congress.gov
Updated January 30, 2024
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 that 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,
which has appropriated well over $200 billion for a broad
range of BMD research and development programs and
deployment of BMD systems here and abroad.
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, U.S.
deployed forces, and U.S. allies and partners against
ballistic missiles of all ranges and in all phases of flight.
The FY2024 budget request is $28.9 billion for overall
missile defeat and defense, including $9.2 billion for
BMDS.
Ballistic Missile Threats
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 (km) to more than
10,000 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 allies and partners; however, China and, in
particular, Russia also have significant numbers of ICBMs.
Russia continues to possess intermediate-range ballistic and
cruise missiles (3,500-5,500 km), which led to the U.S.
withdrawal from the 1987 Intermediate Nuclear Forces
(INF) Treaty. The 2022 Missile Defense Review
additionally identifies ballistic missile threats from North
Korea and Iran.
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 has flight-tested two types of road-mobile
ICBMs that have the range to strike the U.S. homeland. The
Defense Intelligence Agency (DIA) has assessed that
“North Korea’s continued development of ICBMs, IRBMs,
and [submarine-launched ballistic missiles] demonstrates its
intention to bolster its nuclear delivery capability.”
The intelligence community 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 ICBM program.
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. allies and partners 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.
The Major Elements of the U.S. BMDS
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.
Ground-Based Midcourse Defense (GMD)
Since 2004, the United States has deployed a force of 44
Ground-based Interceptors (GBI) at Fort Greely, AK, and
Vandenberg Air Force Base, CA. 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 Iran. Although the GMD system has been praised by
senior military leaders, it does have a somewhat mixed
flight test record, having failed 8 out of 18 intercept
attempts between 1999 and 2018.
Terminal High Altitude Area Defense (THAAD)
THAAD is a highly mobile, rapidly deployable BMD
system designed to shoot down incoming short- and
