Fact Sheet: U.S. Ballistic Missile Defense


The U.S. is engaged in a prolonged, highly expensive program to develop a layered complex of weapons programs tied together in an integrated system of systems to defend the U.S. homeland, troops and facilities abroad, and some allies, from attacks by ballistic missiles.

According to Missile Defense Agency (MDA) estimates, Congress has appropriated $164.7 billion for the Agency’s programs between FY 1985 and FY 2014. That total does not include spending by the military services on programs such as the Patriot system or the many tens of billions of dollars spent since work on anti-missile systems first began in the 1950’s.

Progress has been made in enhancing the efficacy of some U.S. missile defense systems and the overall effort enjoys strong bipartisan support in Congress. In addition, many U.S. allies place a high value on missile defense cooperation with the United States. Despite the enormous financial investment, however, questions remain about the technical viability, cost-effectiveness, and strategic benefit of the U.S. missile defense program, particularly the system in Alaska and California designed to protect the United States against a potential limited long-range missile attack. Missile defense continues to be plagued by a number of decades-old, intractable issues that remain unsolved. Examples include:

  • Terrorism and asymmetric warfare against which missile defenses have little if any effect.
  • Defense against cruise missiles, a common missile threat.
  • The incentive for adversaries to build more offensive missiles to overwhelm missile defenses.
  • Vulnerability to confusion by countermeasures, including decoys, stealth and debris from rocket stage separations.
  • The slow pace of testing, and excessively scripted tests that fail to demonstrate an effective operational capability.
  • Excessive costs that add to the nation’s fiscal deficits.
  • Some U.S. missile defense programs are a major obstacle to improved relations with Russia.

Ballistic Missile Basics

Ballistic missiles are powered initially by a rocket or series of rockets in stages, but then follow an unpowered, parabolic trajectory toward the target.

There are four general classifications of ballistic missiles based on their range, or the maximum distance the missile can travel:

  • Short-range: less than 1,000 kilometers (approximately 620 miles).
  • Medium-range: between 1,000 to 3,000 kilometers (approximately 620-1,860 miles).
  • Intermediate-range: between 3,000 to 5,500 kilometers (approximately 1,860-3,410 miles).
  • Long-range intercontinental (ICBM): more than 5,500 kilometers (approximately 3,410 miles).

Short range ballistic missiles are sometimes referred to as “tactical” ballistic missiles; medium-range missiles as “theater” ballistic missiles; and ICBMs and other long-range ballistic missiles as “strategic” ballistic missiles.

Ballistic missiles have three stages of flight:

Boost Phase begins at launch and lasts until the rocket engine(s) stops firing and the missile begins unpowered flight. Depending on the missile, boost phase can last three to five minutes. Most of this phase takes place in the atmosphere (endoatmospheric).

  • The bright, hot booster rocket exhaust enables detection and tracking by missile defense sensors, such as space surveillance systems. Decoys or countermeasures designed to confuse defenses cannot be deployed during the boost phase.
  • Although missiles move relatively slowly during this phase, the time available to intercept missiles during boost phase is brief (typically 80 to 120 seconds). Thus far, boost-phase defense has proved impractical.

Midcourse Phase begins after the rocket(s) stops firing. During the early part of the midcourse stage, the missile ascends toward its apogee; while during the latter part, the missile descends toward Earth. This is the longest phase of a missile’s flight, and can last as long as 20 minutes for ICBMs. Almost all of the midcourse phase of intermediate- and long-range missiles takes place in space (exoatmospheric).

  • The missile’s payload, including the warhead(s) and countermeasures against defenses, is released during this phase. According to recent reports by the Defense Science Board and the National Academy of Sciences, deployment of the payload and countermeasures can be achieved very rapidly after booster burnout, typically in less than 100 seconds, before the missile reaches apogee.
  • The midcourse phase provides the best opportunity for interception.
  • Midcourse interception requires large, heavy missiles that must be supported by sophisticated radar and other sensors. Midcourse intercepts are also vulnerable to debris accompanying the attacking warhead as well as by decoys and other countermeasures.

Terminal Phase begins when the detached warhead(s) reenter the Earth’s atmosphere and ends upon impact or detonation. During this phase, which can last for less than a minute, strategic warheads can be traveling at speeds greater than 3,200 kilometers per hour.

  • Smaller, lighter interceptor missiles and shorter-range radars can be employed during the terminal phase. Decoys and countermeasures present less of a problem as the stress of reentry into the atmosphere strips them off the warhead.
  • However, there is a very short time window for interception during the terminal phase, often only about 30 seconds, and only a limited battle space can be covered by terminal interceptors.

Defeating ballistic missiles with a defensive system involves four functions: detection, discrimination (distinguishing the missile or warhead from accompanying debris, decoys and other countermeasures), fire control (predicting the target location and guiding the interceptor), and killing (hitting the missile or warhead with the interceptor).

Short- and medium-range ballistic missiles pose different challenges and opportunities for intercept than defenses against longer-range missiles.

  • North Korea and Iran have deployed hundreds of mostly conventionally-armed tactical and theater missiles; but as of now, they have not demonstrated a long-range missile capability.
  • Shorter range systems move more slowly, whereas long range systems and ICBMs may be traveling at roughly 17,000 mph or more. Reportedly, the U.S. Minuteman III ICBM has a speed of about 15,000 mph at burnout.
  • Short range systems travel in the atmosphere; and medium range ballistic missiles spend only a relatively small part of their trajectory in space. The drag from traveling in the atmosphere can strip off decoys or debris from rocket stage separation. In the vacuum of space, everything travels at the same speed, mixing in debris and decoys with the warhead, thereby making identification of the warhead very difficult.
  • To reach longer range systems, the interceptor has to travel much faster and farther to reach the target in space. And then when the interceptor gets into the vicinity, it may have only a brief moment to make a course correction.
  • On the other hand, short range systems also can be difficult to intercept because the defender may have little time to find and engage the incoming missile.

U.S. Missile Defense Systems

Defense against Long-Range Ballistic Missiles

The Ground-Based Mid-Course System (GMD)

GMD, designed to defend the U.S. homeland against ICBMs, is the most complex and costly component of the U.S. missile defense system. The current operationally-deployed interceptors are intended to counter a limited attack by a rogue state with a single or very few missiles. In 2002, President Bush ordered the deployment of ground-based interceptors by 2004 to counter an ICBM attack by North Korea or Iran.

The Pentagon currently deploys 30 ground-based interceptors (GBIs), including 26 at Fort Greely, Alaska, and four at Vandenberg Air Force Base, California. On March 15, 2013, Secretary of Defense Chuck Hagel announced that the Pentagon will deploy an additional 14 interceptors at Fort Greely, increasing the number of deployed GBIs to 44. The additional interceptors are scheduled to be deployed by 2017, at an estimated cost of about $1 billion. These interceptors will include the newer kill vehicle, known as the Capability Enhancement (CE) – II.

Problems with GMD

GMD currently remains a prototype system. It was rushed into the field after President George W. Bush ordered a crash effort to deploy an initial operating defense capability in 2002. Then Secretary of Defense Donald Rumsfeld exempted the Missile Defense Agency from standard procurement rules and testing standards, freeing it to use research and development money to buy and deploy the system quickly. The hurried deployment has compromised the system’s effectiveness and reliability. According to then Missile Defense Agency Director Gen. Patrick O’Reilly, the interceptors currently fielded in Alaska and California are “more akin to prototypes than production-representative missiles.

GMD has a record of testing failures (see “U.S. Missile Defense Record” below). There have been only nine hits out of 17 tries of the system since 1999. About a third of the kill vehicles now in place are the same model that failed two tests in 2010. Furthermore, because each kill vehicle is somewhat unique, even a successful test cannot predict the performance of the other interceptors.

An operationally configured interceptor has yet to be tested against a target with ICBM range and speed, and there are no near term plans to do so.

The GMD system’s Achilles heel is the inability to deal with countermeasures. Several authoritative sources have warned that any country capable of fielding an ICBM can easily employ effective countermeasures to prevent discrimination between warheads and simple decoys or debris in the target complex. A 2011 Defense Science Board report concluded that while “the ability to dependably discriminate reentry vehicles from penetration aids and other objects,” is essential to an effective missile defense system, “discrimination in the exo-atmosphere is still not a completely solved problem.” This encouraged as yet unsuccessful efforts to develop the capability to intercept hostile ICBMs in their boost phase, before their payloads could be released from the missile.

The Kinetic Energy Interceptor, a mobile land- and sea-based weapon, was canceled in 2009 after expenditures of $4.5 billion over eight years because it proved impractical to design a fast enough interceptor to catch up with ballistic missiles during the short duration of their boost phase. The Airborne Laser program envisioned mounting an array of chemical laser systems aboard modified Boeing 747 cargo aircraft. In addition to serious technical problems with the laser apparatus itself, a basic limitation proved to be the lack of sufficient range of the laser beam; after spending $5.2 billion on the program, the test aircraft was retired.

Expanding GMD to the U.S. East Coast

Congress, concerned about Iran’s efforts to develop ICBMs, has urged the Pentagon to commit to building an additional missile defense site on the East Coast. The fiscal 2013 National Defense Authorization Act ordered the Pentagon to identify at least three possible locations for a third interceptor site, two of which must be on the East Coast. Four possible interceptor sites are being considered: Fort Drum, New York; SERE Training Area at Naval Air Station, Portsmouth, Maine; Camp Ravenna Joint Training Center in Ohio; and Fort Custer Training Center in Michigan. In July 2014, the Defense Department sent out a formal notice about conducting environmental impact studies of the four possible sites.

In a letter to the chairman of the Senate Armed Services Committee, the current head of the MDA, Vice Adm. James Syring, and head of the Army’s Space and Missile Defense Command, stated that there is “no validated military requirement to deploy an East Coast missile defense site.”

In June 2013, the Congressional Budget Office estimated that putting a GMD system on the east coast consisting of 20 interceptors will cost $3.4 billion over the next five years. By most accounts, the Pentagon could not afford to fund the East Coast site without relief from spending limits.

June 2014 GMD Test

On June 23, 2014, a ground-based interceptor fired from Vandenberg Air Force Base in California destroyed a mock enemy warhead above the Pacific Ocean. The intercept was achieved by a CE-II kill vehicle model, the first success in three tries. This intercept was the GMD system’s first success in the last four attempts since December 2008, but the Pentagon may consider the one test as sufficient validation for the deployment of 14 more interceptors at Fort Greely, Alaska, costing about $1 billion.

Defense against Short and Medium Range Ballistic Missiles

The Patriot Advanced Capability (PAC-3)

The PAC-3 is the most mature system in the U.S. missile defense arsenal. It is a “hit-to-kill,” system mounted on a mobile launcher, and it employs sensors to track and intercept missiles in their terminal phase. Each PAC-3 battery can hold up to 16 missiles. PAC-3 batteries have been widely deployed by the United States and its allies in multiple theatres. During the invasion of Iraq in 2003, the PAC-3 destroyed several short range Iraqi missiles; but it also shot down two friendly aircraft, killing three airmen.

The Theater High Altitude Area Defense (THAAD)

The THAAD system employs a single rocket booster on a truck-mounted launcher to attack short- and medium-range missiles in their terminal phase at higher altitudes than the PAC-3. A THAAD battery currently consists of three launchers, 24 interceptor missiles, a radar, a fire control and communications system, and other support equipment. The first two THAAD batteries have been conditionally accepted by the Army, but all planned capabilities have not yet been reliably demonstrated. In early April 2013, the Pentagon announced that it would deploy one THAAD battery to Guam in response to North Korea’s provocative behavior.

The Aegis sea-based Ballistic Missile Defense

While limited in the scope of its capability, the Aegis ballistic missile defense system is widely considered to be an effective element of U.S. missile defense. Originally designed to protect naval vessels against aircraft and cruise missiles, the Aegis system evolved to counter short range ballistic missiles in their terminal phase of flight with its SM-2 missile. The more advanced SM-3, Block IA, missile has a three-stage interceptor that employs hit-to-kill technology to attack short and medium range ballistic missiles during the midcourse stage of their flight. Key components of the Aegis system include the Aegis Weapons System software, the SPY-1 radar, battle management and command and control systems, and SM-3 missiles. The system is deployed on the U.S. Navy’s cruisers and destroyers, allowing the Missile Defense Agency (MDA) to move its defense capabilities closer to an enemy’s launch sites. The U.S. Navy currently has 26 Aegis-equipped ships (5 Aegis equipped cruisers and 21 destroyers); 16 are assigned to the Pacific Fleet and 10 to the Atlantic Fleet.

The European Phased Adaptive Approach (EPAA)

The Obama administration announced in September 2009 that the U.S. would pursue a “Phased Adaptive Approach” (EPAA) in its ballistic missile defense program in Europe. The EPAA is designed to protect U.S. assets, personnel, and the European population from the threat posed by Iranian short and intermediate range ballistic missiles. Its main component, the Aegis BMD system, is being deployed in three phases from 2011 through 2018. The system will ultimately involve “scores” of interceptors which will allow it to handle larger attacks involving 20 to 50 enemy missiles. It is part of an integrated NATO missile defense system.

EPAA replaced the George W. Bush administration’s plan to deploy in Europe a third GMD site, in addition to GMD interceptors in Alaska and California. This would have consisted of 10 ground based interceptors in Poland and supporting radar in the Czech Republic.

Phase 1 of EPAA included Aegis cruisers and destroyers carrying SM-3 Block 1A missiles and a forward deployed radar in Turkey. In March 2011, the USS Monterey was deployed to the Mediterranean Sea, becoming the first in a sustained rotation of ships in support of EPAA.

In Phase 2, land-based SM-3 Block IB interceptors, also known as Aegis Ashore, will be fielded in Romania in 2015.

Phase 3 envisions deployment in 2018 of another Aegis-Ashore site in Poland, with upgraded SM-3 Block IIA interceptors able to intercept intermediate-range missiles.

The initial EPAA plan included a fourth phase to deploy SM-3 Block IIB interceptor, able to intercept Iranian ICBMs prior to the release of the missile’s payload, called “early intercept.” The technological feasibility of early intercept was a subject of intense scrutiny. In September 2011, the Defense Science Board released a study that concluded that early intercept is “not realistically achievable.”

On March 15, 2013, Secretary of Defense Chuck Hagel announced the cancellation of the SM-3 IIB deployment in Europe, due to technical problems and funding considerations. Hagel reaffirmed the administration’s “ironclad” commitment to NATO, and its plans to move forward with the first three phases of the EPAA, including the sites in Poland and Romania.

U.S. Missile Defense Testing Record

Note: Official U.S. testing data for its ballistic missile defense systems has been a subject of significant controversy regarding the accuracy of published results. Experts have argued that the tests are “scripted for success,” with some failures discounted as “no-tests.” Testers are provided data they would not have access to in actual combat situations.

According to the Missile Defense Agency’s official report, as of June 22, 2014, 65 of 81 hit-to-kill intercept attempts have been “successful” across all programs since the integrated system began to be developed in 2001.

The overall test record includes the Ground-based Midcourse Defense, Aegis Ballistic Missile Defense, Terminal High Altitude Area Defense (THAAD), and PATRIOT Advanced Capability-3 (PAC-3). 44 of 56 hit-to-kill intercept attempts have been achieved for THAAD, Aegis BMD, and GMD test programs since 2001. Of these, 9 of 17 GMD intercept attempts have been successful since 1999. 28 intercepts in 34 at sea attempts have been successful for the Aegis system. All 11 recent THAAD intercepts have been deemed successful.