Order Code RS22120
Updated January 5, 2007
Ballistic Missile Defense:
Historical Overview
Steven A. Hildreth
Specialist in National Defense
Foreign Affairs, Defense, and Trade Division
Summary
For some time there has been a growing sense of urgency to develop and deploy
effective missile defenses against a range of long and short range ballistic missile
threats. Although many might believe this to be relative new to U.S. national security
objectives, such interest has been ongoing since the 1960s, and many current
technologies being investigated date their start to the early 1980s. This effort has been
challenging technically1 and politically controversial. Some $110 billion has been spent
since the mid-1980s; Congress appropriated $9.3 billion in FY2006. Many observers
expect that the 110th Congress will review the current technology and BMD test program
in 2007. This report provides a brief overview of U.S. efforts to date. It may be updated.
Introduction
Since the mid-1980s, many decision makers and others have demonstrated serious
interest in deploying ballistic missile defense (BMD) systems capable of defending the
United States from missile attack. Events over the past fifteen years contributed to
strengthen these views. The collapse of the Soviet Union in 1991 heightened concerns
about the possibility of an accidental or unauthorized launch of ballistic missiles from the
remnants of that nation. The Persian Gulf War in 1991, with Iraq’s use of Scud missiles,
proved to many that the growing threat posed by ballistic missiles had to be addressed.
The proliferation of ballistic missile technologies, including sales from nations such as
China, Russia, and North Korea to nations such as Iran, Syria, and Pakistan became more
worrisome to many. Finally, many also argue that some U.S. adversaries, such as North
Korea, are developing longer-range missiles that might reach the United States.
But interest in missile defense stretches back much further than the 1980s. In fact,
efforts to counter ballistic missiles have been underway since the dawn of the missile age
1 For a 25-year review of the major BMD technology thrust, see CRS Report RL33240, Kinetic
Energy Kill for Ballistic Missile Defense: A Status Overview, by Steven A. Hildreth.

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at the close of World War II. Numerous programs were begun, and only a very few saw
completion to deployment. Technical obstacles have proven to be tenacious, and systems
integration challenges have been more the norm, rather than the exception. Since 1985,
the United States has spent about $110 billion on missile defense efforts, and in 2004
deployed a small-scale national-level missile defense, which has yet to be tested fully
successfully in its deployed configuration.
This short report provides a brief overview of the history of the missile defense
efforts undertaken to defend the United States. It begins with a brief summary of the
provisions of the 1972 ABM Treaty, which shaped most of the history of the U.S. BMD
effort, and includes a short review of U.S. programs leading to the current program.
The 1972 Anti-Ballistic Missile (ABM) Treaty
Negotiations with the Soviet Union on the Anti-ballistic Missile (ABM) Treaty
began in November 1969. Early on the United States proposed that the treaty limit Russia
to one deployment site around Moscow (which it was building) and permit the United
States to deploy four sites around ICBM fields, which was the U.S. program at the time
(construction had begun on a site near Grand Forks, ND). The Soviets rejected this
proposal, insisting any agreement include equal limits on each nation. They had the same
reaction when the United States proposed that the treaty permit either nation to deploy one
site at its capital or two sites at ICBM fields. Eventually, the Nixon Administration
agreed to accept parity in ABM deployments; each nation could deploy two sites, one
around its capital and one around an ICBM field. This permitted the continued
construction of each nation’s existing ABM site.
Signed in May 1972, the Anti-Ballistic Missile (ABM) Treaty prohibited the
deployment of ABM systems for the defense of the nations’ entire territory. It permitted
each side to deploy limited ABM systems at two locations, one centered on the nation’s
capital and one at a location around ICBM silo launchers. When it became clear that
neither nation would complete a second site, the two sides agreed in a 1974 Protocol that
each would have only one ABM site, located either at the nation’s capital or around an
ICBM deployment area. Each ABM site could contain no more than 100 ABM launchers
and 100 ABM interceptor missiles. The Treaty also specified that in the future any radars
that provided early warning of strategic ballistic missile attack had to be located on the
periphery of the national territory and oriented outward. The Treaty banned the
development, testing, and deployment of sea-based, air-based, space-based, or mobile
land-based ABM systems and ABM system components (these included interceptor
missiles, launchers, and radars or other sensors that can substitute for radars). The Treaty
placed no restrictions on the development, testing, or deployment of defenses against
shorter range missiles. Although the United States withdrew from the ABM Treaty in
2002, the treaty profoundly shaped U.S. efforts up to that point.
History of NMD in the United States
Sentinel and Safeguard Programs. The United States has pursued research
and development in anti-ballistic missile (ABM) systems since the early 1950s. In the
mid-1960s it developed the Sentinel system, which would have used ground-based,
nuclear-armed interceptor missiles deployed around a number of major urban areas to

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protect against Soviet missile attack. Many analysts recognized that such protection
would be limited, in part because the Soviet Union could probably saturate the system
with offensive warheads and just a few warheads could achieve massive damage against
a “soft” target like a city. In response, supporters argued that the system could provide
a “thin” defense of U.S. cities against an attack by an anticipated Chinese intercontinental
ballistic missile (ICBM) force.
In 1969, the Nixon Administration renamed the system “Safeguard,” and changed
its focus to deployment around offensive (i.e., nuclear-tipped ICBMs) missile fields,
rather than cities, to ensure that these missiles could survive a first strike to ensure
retaliation against the Soviet Union. Many in Congress objected to the program, citing
its costs, technical uncertainties, and the risk of accelerating the arms race. Congress
almost stopped the program in 1969, when the Senate voted 50-50 to approve an
amendment halting construction. Safeguard continued, however, when Vice President
Agnew broke the tie with a vote for the program. Nevertheless, sentiment against ABM
deployments and in favor of negotiated limits on ABM systems was growing.
The United States completed its nuclear interceptor ABM site near Grand Forks,
North Dakota. It operated for nine months in 1974 and 1975, then was shut down because
it proved to be not cost-effective. The facilities at that location, however, continued to
count under the ABM Treaty because it had not been dismantled according to a classified
post-Treaty agreement reached with the Soviet Union. Russia continues to this day to
operate its ABM site around Moscow.
U.S. research and development into ABM systems, especially for ICBM protection,
continued, albeit at lower budget levels through the late 1970s. By the time of the Carter
Administration, however, spending on missile defense programs had began to rise again,
primarily as a means to defend the newest generation of U.S. ICBMs — the MX missile
system.
The Strategic Defense Initiative (SDI). The Reagan Administration continued
to increase funding for defenses against ICBMs begun under the Carter Administration.
But, in March 1983, President Reagan announced an expansive, new effort to develop
non-nuclear ballistic missile defenses that would protect the United States against a full-
scale attack from the Soviet Union. Although the Strategic Defense Initiative (SDI)
remained a research and development effort, with little testing and no immediate
deployments, President Reagan and the program’s supporters envisioned a global
defensive system with thousands of land-, sea-, air-, and space-based sensors and
interceptors. This defensive “shield” would employ both non-nuclear interceptor missiles
and more exotic laser or x-ray devices designed to destroy incoming missiles. With these
technologies, the United States would replace deterrence with defense in its effort to
protect itself from Soviet attack. However, as cost estimates and technical challenges
increased, the Reagan Administration scaled back its objectives for SDI. It announced
that it would begin with a “Phase I” deployment of land-based and space-based sensors
and interceptors. This system would not provide complete protection from Soviet attack,
but would, instead, seek to disrupt the attack enough to call into question the attack’s
effectiveness. Phase I of SDI would, therefore, according to their arguments, enhance
deterrence, while the United States continued to seek a way to replace deterrence with
defense. Although Congress largely supported BMD research and development, it
generally opposed plans for significant BMD deployments at that time.

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The Reagan Administration and the program’s supporters recognized that many of
the technologies pursued under SDI would not be allowed by the ABM Treaty when they
entered the testing or deployment phases. Therefore, the Reagan Administration outlined
a new interpretation of the ABM Treaty that it hoped would allow for the testing of space-
based and exotic missile defense technologies. Many in Congress at that time objected
to this re-interpretation of the ABM Treaty, with Senator Sam Nunn mounting a
particularly comprehensive defense of the traditional interpretation of the Treaty.
Throughout this period, Congress tendered strong support for the ABM Treaty. The
Reagan Administration also opened new negotiations with the Russians, known as the
Defense and Space talks, in an effort to reach agreement on modifications to or a
replacement for the ABM Treaty.
Global Protection Against Limited Strikes (GPALS). The first Bush
Administration responded to the costs and technical challenges of Phase I and the
changing international political environment with a further contraction of the goals for
SDI. Instead of seeking to protect the United States against a large-scale attack, the
United States would seek to deploy a defensive system that could provide Global
Protection Against Limited Strikes (GPALS); a more modest version of the original SDI
vision. This new focus recognized that the demise of the Soviet Union had reduced the
likelihood of a large-scale attack, but also the increased likelihood of a small accidental
or unauthorized attack. In addition, this type of ballistic missile defense would have
sought to protect the United States, its forces, and allies against an attack by other nations
who had acquired relatively small numbers of ballistic missiles.
The Bush Administration envisioned a GPALS system that would have included up
to 1,000 land-based interceptors and perhaps another 1,000 space-based interceptors,
along with space-based sensors. The Administration recognized that this system would
have exceeded the limits in the ABM Treaty. It therefore held negotiations with the
Russian government in 1992 in an effort to identify a more cooperative and flexible
regime to replace the ABM Treaty. The Clinton Administration suspended these
negotiations in 1993, when it also scaled back U.S. objectives for a national missile
defense program. Meanwhile, some in Congress, notably Senator Nunn, had argued since
the late 1980s for the deployment of a more limited NMD system, that would comply with
the ABM Treaty, to protect against limited or accidental attacks.
National Missile Defense Technology Development. The Clinton
Administration restructured BMD programs to reflect the results of the 1993 Bottom Up
Review, a major DOD-wide review of U.S. military plans and programs. At the time, it
decided to emphasize missile defense deployment geared toward short-range missile
threats, and focus national level efforts on technology development. Secretary of Defense
Aspin noted at the time that these program changes reflected an assessment that the
regional ballistic missile threat already existed, while a ballistic missile threat to the
United States per se might emerge only in the future. This raised questions about the
need for an NMD system in the near- to mid-term, particularly as compared with the need
for robust theater missile defense efforts. The Department of Defense also determined
that these programs would still be conducted in compliance with the 1972 ABM Treaty.
Key legislation was passed during this time. The Missile Defense Act of 1995 (in
P.L. 104-106 — National Defense Authorization Act for Fiscal Year 1996) declared it the
policy of the United States to: (1) develop as soon as possible affordable and

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operationally effective theater missile defenses; (2) develop for deployment a multiple-site
national missile defense system that is affordable and operationally effective against
limited, accidental, and unauthorized ballistic missile attacks on the United States, and
which can be augmented over time as the threat changes to provide a layered defense
against limited, accidental, or unauthorized ballistic missile threats; (3) initiate
negotiations with Russia as necessary to provide for the national defense systems
envisioned by the act; and (4) consider, if those negotiations fail, the option of
withdrawing from the ABM Treaty.
The Clinton Administration adjusted its efforts and adopted a new strategy for
national missile defense. In 1996, the Clinton Administration adopted a 3+3 strategy, to
guide development and potential deployment. Under this strategy, the United States
would develop a national missile defense system to defend the United States against
attacks from small numbers of long-range ballistic missiles launched by hostile nations,
or, perhaps, from an accidental or unauthorized launch of Russian or Chinese missiles.
The strategy envisioned continued development of NMD technologies during the first
three years (1997-2000), followed by a deployment decision (in 2000) if the system were
technologically feasible and warranted by prospective threats. If a decision to deploy an
NMD system were made, the plan then was to deploy it within the second three year
period (2000-2003). Development and deployment was to be conducted within the limits
of the ABM Treaty. This approach was later modified to allow a longer lead time for
possible deployment (possibly 2005), and according to the Pentagon at that time, to
reduce the amount of program risk. Ultimately, in September 2000, President Clinton
decided not to authorize deployment of a national missile defense at that time. He stated
that he could not conclude “that we have enough confidence in the technology, and the
operational effectiveness of the entire NMD system, to move forward to deployment.”
National Missile Defense Acquisition. President George W. Bush entered
office prepared to advance ballistic missile defense deployment as a key national security
objective. The Bush Administration substantially increased funding for missile defense
programs and laid the foundation for withdrawal from the 1972 ABM Treaty, which was
announced in June 2002. Much of the Bush Administration’s argument centered around
a different strategic environment from 1972: Soviet forces no longer threatened the United
States and the greater threat came from the proliferation of ballistic missiles and weapons
of mass destruction from other countries. Special concern was focused on rogue states
and terrorism. The Russian government gave little opposition to the Administration’s
decision to withdraw from the treaty, and potential allied criticism in Europe was notably
muted.
Also in 2002, the President announced his decision to deploy a limited ballistic
missile defense system against long-range missiles by the fall of 2004. Although this goal
was met with the deployment of five ground-based interceptors in silos in Alaska, on-
going technology problems have not yet demonstrated the operational capability of that
deployed system. Current plans are to continue testing and deployment of those
interceptors in Alaska, California, and eventually at a third site in Europe. Throughout,
Congress has been highly supportive of the Bush Administration’s efforts.

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History of TMD in the United States
U.S. efforts to develop effective defenses against shorter range ballistic missile
threats to U.S. forces deployed overseas grew out of the Army’s Patriot air defense
system, which began in the 1960s. As Patriot developed further in the 1980s, some
argued for its potential also as a theater missile defense capability. Although the
Pentagon, Army, and the SDI Organization initially were not supportive of the effort at
first, Congress increasingly argued successfully for Patriot’s development of an anti-
tactical missile (ATM) defense. By the time of the 1991 Persian Gulf War, the Patriot
ATM had experienced a remarkably successful test record.2 Acquisition of Patriot
missiles for Desert Storm was accelerated after Iraq invaded Kuwait. On the battlefield,
however, Patriot’s success, or lack of it in Desert Storm, remains a subject of controversy
despite most public perceptions of unequivocal success.3
Nonetheless, Congress and the Department of Defense determined subsequently that
the Patriot concept to defend against shorter range ballistic missile threats to U.S. forces
overseas warranted further support. The Patriot system had been upgraded several times
by the time of the recent war against Iraq. On the battlefield, Patriot was considered more
successful than in 1991, but with mixed results.4 Congress and the Pentagon continue to
support development of highly effective TMD systems, especially a maritime TMD
capability built around existing naval systems and infrastructure that have been deployed
or in development for decades.5 In terms of program and testing success, most observers
agree that the U.S. effort to develop and deploy effective BMD against short-range
missiles has been more successful relative to the U.S. effort to develop and deploy
effective BMD against long-range or strategic ballistic missiles.
2 CRS Report 91-456F, The Patriot Air Defense System and the Search for an Antitactical
Ballistic Missile Defense, by Steven A. Hildreth and Paul C. Zinsmeister (available from author
upon request).
3 Hearings before the House Government Operations Sub-committee on Legislation and National
Security, April 7, 1992, on Patriot Performance in Desert Storm.
4 CRS Report RL31946, Iraq War: Defense Program Implications for Congress, by Ronald
O’Rourke (section on Ballistic Missile Defense).
5 CRS Report RL33745, Sea-based Ballistic Missile Defense – Background and Issues for
Congress, by Ronald O’Rourke.

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