S. ballistic missile defense up to the ABM Treaty The United States has been pursuing ballistic missile defense, in

par-ticular the defense of U.S. territory against intercontinental-range ballis-tic missiles (ICBMs), for nearly as long as such missiles have existed.

In the context of this chapter, “strategic” defense means the de-fense of a national territory against strategic missiles: ICBMs or their submarine-launched equivalents. In the 1970s and earlier, such sys-tems were frequently referred to simply as Anti-Ballistic Missile (ABM) systems. The term National Missile Defense (NMD) is now commonly used to describe the defense of national territory from attack by strate-gic ballistic missiles.

In 1958, a U.S. Army system known as Nike-Zeus was selected for development.¹ Nike-Zeus was intended to provide a defense of a number of relatively small areas, such as cities or military installa-tions, from Soviet ICBMs. The system would have used four different types of mechanically-scanning radars and a large, command-guided, nuclear-armed interceptor missile known as the Zeus. The Zeus had a 400 kiloton nuclear warhead and a range of about 130 km. Critics of the system argued that its radars were both vulnerable to attack and could be overwhelmed by even a small number of attacking missiles, that the system could be easily defeated by penetration aids, and that it would be very expensive to expand the system to nationwide coverage.

In late 1961, President Kennedy announced his decision not to deploy the Nike-Zeus system.

Development of the system’s technology continued, however.

In 1962, a Zeus interceptor launched from Kwajalein Atoll in the Pacific made the first successful test intercept of an ICBM warhead. The

in-terceptor got close enough to destroy the warhead of the target missile (launched from California), had the interceptor actually been armed with a nuclear warhead.

In early 1963, the Army announced a restructuring of the Nike-Zeus program, which was renamed Nike-X. Nike-X replaced the mechanical-ly-scanning radars of Nike-Zeus with two types of phased-array radars, which were capable of dealing with many more targets simultaneously and were less vulnerable to the effects of nuclear explosions. The Zeus interceptor was upgraded to have a much greater range and a much larger nuclear warhead (5 megatons) and was renamed the Spartan.

The longer range of the Spartan (500-800 km) gave the system the abil-ity to cover much larger areas than Nike-Zeus. A second type of nuclear-armed interceptor, the very-high-speed, short-range Sprint, was added.

The Sprint could attempt intercepts after the atmosphere had filtered out penetration aids and would be used to defend point targets such as mis-sile silo fields and cities.

In September 1967, after failing to get the Soviet Union to agree to consider limits on ABM systems and to begin negotiations on offensive nuclear forces, the United States announced it would begin deployment of a nationwide ABM system. This system, based on Nike-X technology, was subsequently named Sentinel.

Sentinel was announced as a thin defense of the U.S. population against a future Chinese ICBM threat. It was intended to provide a defense of the entire United States against small scale attacks, with an option to add addi-tional Sprint interceptors for a denser defense of ICBM silo fields. It would have deployed at least seventeen missile defense sites, including one each in Alaska and Hawaii. Most sites would have been located in the vicinity of major cities, which provoked strong local opposition. Each site would have a phased-array Missile Site Radar (MSRs) and Spartan interceptors.

Six of the sites along the northern U.S. border (including one in Alaska) would have been equipped with long-range, phased-array Perimeter Acquisition Radars (PARs). Some sites, particularly those containing ICBM silos or (PARs), would have Sprint interceptors as well. Initial plans called for a total of 480 Spartans and 220 Sprints.

When President Richard Nixon took office in 1969, he immedi-ately suspended Sentinel construction. In March 1969, he announced

Chapter 3. U.S. BMD Evolution Before 2000 53

a restructuring of Sentinel, now renamed Safeguard. Safeguard used the same system elements as Sentinel, but with changes in deployment locations and on the defense’s emphasis. While Safeguard focused on defense of missile silo fields and bomber bases instead of cities, it was still intended to be able to provide a thin coverage of the contiguous 48 states. Although Safeguard was an improvement in many respects over Nike-Zeus, it was still extremely vulnerable to countermeasures, particularly to a direct attack on the system’s radars.²

Despite moving the system’s interceptors away from cities, Safeguard was still controversial – in 1969, the Senate approved beginning de-ployment by a 51-50 vote – and the system was in part sold as a bar-gaining chip.³ By the early 1970s, construction of the first two sites, at Grand Forks, ND, and Malmstrom Air Force Base, MT, had begun.

After the 1972 ABM Treaty and its 1974 protocol limited both the United States and the Soviet Union to only a single ABM site, the United States chose to proceed with its system at Grand Forks. This site, with a long-range Perimeter Acquisition Radar (PAR), a Missile Site Radar, and 30 Spartan and up to 70 Sprint interceptors, was declared operational on October 1, 1975.

It was clear that the single Safeguard site did not provide enough capability to justify even its operating costs. In late 1975, Congress ordered the system shut down, which was completed by the end of January 1976.

The ABM Treaty

In 1972, in conjunction with the SALT I Treaty limiting offensive strategic nuclear weapons, the United States and Soviet Union signed the Anti-Ballistic Missile (ABM) Treaty. The ABM Treaty was based on a mutual understanding that neither country could build an effective defense against the other’s large nuclear arsenal, and that attempting to do so would be both extremely costly and potentially destabilizing, and could lead to an offense-defense arms race.

The Treaty placed strict limits on the strategic ballistic missile de-fense activities of the United States and the Soviet Union (later Russia).

It prohibited either country from deploying a nationwide strategic de-fense system or from establishing the infrastructure for such a deploy-ment. To prevent the establishment of such an infrastructure, limits were placed on the deployment of large phased-array radars, which were re-garded as the longest lead-time element of a strategic ballistic missile defense system. Development or testing of mobile or sea-, air-, or space-based strategic defenses, or of strategic defenses operating on “other physical principles,” was prohibited. The Treaty also prohibited giving non-strategic defense systems, such as theater missile defense (TMD) systems, capabilities to counter strategic missiles.

The Treaty allowed research and development on strategic defenses to continue (because limitations on such activities could not be verified effectively) and specifically permitted testing of fixed, ground-based de-fenses at declared test ranges. In addition, each country was permitted to deploy one (originally two) single-site strategic ballistic missile defense system with up to 100 interceptors located at either the national capital or at an ICBM silo field. All of the components (interceptors, launchers, radars) of the permitted defense had to be at one site, and the defense was limited to protecting an “individual region” of either country.

The Strategic Defense Initiative

Following the ratification of the ABM Treaty and the shutdown of Safeguard, missile defense technology development continued, most clearly evidenced by the fourth (and only successful) test of the Homing Overlay System in June 1984. In this test, a large infrared-homing in-terceptor successfully destroyed a target ICBM warhead in a direct, high-speed collision above the Earth’s atmosphere. This was the first demonstration of the hit-to-kill approach, which would be the basis for most of the missile defense systems the United States would subsequent-ly deploy. Overall, however, the subject of ballistic missile defense had largely faded from public attention.⁴

This situation changed dramatically when President Ronald Reagan announced the Strategic Defense Initiative (SDI) in March 1983. As initially announced, SDI was to provide an impenetrable shield against

Chapter 3. U.S. BMD Evolution Before 2000 55

a massive Soviet attack, thereby making nuclear weapons obsolete. It was to accomplish this by using multiple layers of defenses (boost, mid-course and terminal), both on the ground and in space, much of which relied on technology that did not yet exist (x-ray lasers, space-based par-ticle beams).⁵ This goal was widely viewed as unachievable, particularly by the scientific community, on both technical and financial grounds.

In addition, despite some legalistic arguments to the contrary, it was also fundamentally incompatible with the ABM Treaty. On the other hand, by rejecting the use of nuclear weapons for defense, SDI set a standard that future U.S. missile defenses would be non-nuclear.

As time went by, SDI’s objectives were gradually scaled back.

The Phase I architecture (1987-1989) would have deployed several thousand ground-based and space-based interceptors, with the goal of enhancing deterrence by countering a Soviet first strike by being able to destroy half of the 3,000+ SS-18 Soviet ICBM warheads. The GPALS (Global Protection Against Limited Strikes) system of 1989-1992 aimed only at being able to defend against 200 warheads.

The 1991 Gulf War highlighted attacks by shorter-range theater bal-listic missiles. These attacks, and the subsequently disproved claims that the Patriot system was highly effective in countering them, contrib-uted to a shift away from national defenses toward theater defenses.

By the beginning of 1993, Bill Clinton was President, the NMD budget was shrinking rapidly in favor of TMD, there was no longer any planned deployment date for NMD, NMD efforts were focused on tech-nology development, and the Strategic Defense Initiative Organization had been renamed the Ballistic Missile Defense Organization. Strategic missile defense had once again faded from prominence. Nevertheless, sensor and interceptor technologies that had begun development during this period would be key elements of future U.S. theater and national missile defense programs.

The Clinton National Missile Defense program In early 1995, the Republicans took control of both houses of Congress and soon thereafter began to press for deployment of an NMD

sys-tem. In December 1995, President Clinton vetoed a FY 1996 Defense Authorization bill that would have required the deployment of am NMD system by 2003. Although Congressional Republicans tried each year to pass a similar bill, they did not have the votes to override a veto (or in the Senate to override a filibuster), and no such bill passed until 1999.

However, under this Congressional pressure, the Administration started a program to develop and possibly deploy an NMD program. This was known as the 3 + 3 Program. The 3 + 3 Program called for the de-velopment of a ground-based NMD system in three years (by 2000) that could be deployed in three more years (by 2003). If a decision to deploy was not made in 2000, then system development would continue so that the system would always be three years from deployment with up-to-date technology. If a threat justifying deployment arose, deployment could then begin.

The supporters of the NMD system did not justify it in terms of a de-liberate attack by Russia, but rather cited missile threats from “rogue”

third world countries, an accidental/inadvertent launch by Russia, a de-liberate attack by China, or, finally, the threat of a missile strike by North Korea, which emerged as the most compelling argument. On the other hand, the Clinton Administration argued that there was no immediate threat justifying NMD deployment, that it was unclear if the technology would work, and that its deployment could have adverse consequences for U.S. and international security.⁶ In particular, critics of the system ar-gued that its above-the-atmosphere, hit-to-kill approach made it vulner-able to defeat by simple countermeasures, and that its testing program was highly unrealistic.⁷

The July 1998 Report of the Rumsfeld Commission on the Ballistic Missile Threat to the United States raised the prospect that North Korea or Iran could develop an ICBM within five years and with little warning.⁸ This undercut one of the Clinton Administration’s key arguments against deploying NMD. Together with the launch of North Korea’s Taepodong 1 missile in August 1998, which overflew Japan in a failed attempt to orbit a small satellite, the Rumsfeld Report significantly increased the pres-sure for a near-term decision to begin deployment.

By early 1999, it was clear that both the Senate and the House would pass legislation requiring deployment. Clinton announced that he would

Chapter 3. U.S. BMD Evolution Before 2000 57

not veto the bill if wording were added stating that a deployment should not interfere with nuclear arms negotiations with Russia.⁹ The legislation then passed by wide margins. The National Missile Defense Act of 1999 states, “It is the policy of the United States to deploy as soon as techno-logically feasible an effective National Missile Defense system capable of defending the territory of the United States against limited ballistic missile attack…”¹⁰ However, in September 2000, following two inter-cept test failures, President Clinton announced that he did not “… have enough confidence in the technology and operational effectiveness of the entire N.M.D. system to move forward to deployment.”¹¹ He therefore chose not to deploy at that time, in effect deferring the decision to the next president.

The Clinton 3 +3 Plan

The Clinton 3 + 3 NMD system would have been constructed from a relatively small number of components, most of which were already well along in their development. Since the Ground-Based Midcourse Defense (GMD) that was subsequently deployed was built up out of the components of the 3 + 3 system and several TMD systems simultane-ously being developed, this system and its components are described in more detail below.

In addition to command and control and communication systems, the primary components of the 3 + 3 systems were:

Early Warning Satellites. Early warning satellites in geostationary or-bits 36,000 km above the equator would have provided the first warning of a missile attack. Such satellites could provide warning of a missile launch within about a minute by detecting the bright flame of the mis-sile’s rocket booster. Initially the NMD system would use existing DSP early warning satellites, which had operated effectively for many years.

These would eventually be replaced by more advanced Space-Based Infrared System-High Earth orbit (SBIRS-High) satellites.

Ground-Based Interceptors (GBIs). The GBIs were the interceptor missiles of the system. Each GBI carried a large (55 kg) kill vehicle called the Exoatmospheric Kill Vehicle (EKV), which was released

at the end of the GBI’s flight. The GBI was a large, silo-based three-stage missile capable of accelerating the EKV to speeds of about seven to eight km/second. Once the GBI had placed the EKV on a predicted intercept trajectory, the EKV would use infrared sensors to detect and if necessary to discriminate its intended warhead target. The EKV would then use small thruster motors to maneuver itself into a direct high-speed collision with the warhead.

Ground-Based Radars (GBRs). The GBRs were large X-band phased array radars that would have been the primary missile tracking, discrim-ination, interceptor guidance, and kill assessment sensors of the NMD system. The term “X-band” refers to the 10 GHz operating frequency, corresponding to a wavelength of 3 cm. This high operating frequency al-lowed both a narrower beam to be produced by a given antenna size and a very short range resolution of about 15 cm. This range resolution set the minimum feature size that could be made out on a target, and such a small range resolution was a minimal requirement for dealing with decoys and other countermeasures. With an antenna area of 384 square meters containing 69,632 transmit/receive modules, the GBRs would have been the largest X-band phased-array radars ever built. Ultimately, no GBRs were ever built, although several types of smaller radars based on the same technology were.

Upgraded Early Warning Radars (UEWRs). The UEWRs were pre-ex-isting large phased-array early warning radars that would receive the mi-nor upgrades needed to incorporate them into the NMD system, in which they would have supported the GBRs. Although the UEWRs were in prin-ciple to be capable of guiding interceptors to targets, their low-operating frequency (440 MHz, corresponding to a wavelength of 68 cm) and corre-spondingly poor range resolution (five meters or more) meant that they had essentially no capability to discriminate warheads from decoys.

Space-Based Missile Tracking Satellites. Although not part of the initial deployment, the 3 + 3 System would eventually have deployed a constellation of missile-tracking satellites in low Earth orbits. These satellites, although intended to operate in conjunction with the system’s radars, were to be able to independently detect, track, and if necessary discriminate targets accurately enough to guide interceptors. This sys-tem, then known as the Space-Based Infrared System-Low Earth orbit

Chapter 3. U.S. BMD Evolution Before 2000 59

(SBIRS-Low), would have deployed a constellation of about 20 to 30 satellites to track missiles on a global basis.

The 3+3 system would have been deployed in three phases. The first phase, known as the C-1 system, would have deployed twenty GBI inter-ceptors in silos in central Alaska (in 1999 it was announced that the ini-tial deployment would be increased to 100 GBIs). The primary radar for the system would have been the first GBR, to be built on Shemya Island at the western end of the Aleutian Island chain. Upgraded Early Warning Radars in Britain, Greenland, Massachusetts, California, and Alaska would have supported the GBR as well as providing the sys-tem’s only missile tracking capability against missiles launched from the Middle East. This C-1 system was described as being intended to be able to counter an attack by a “few, simple” warheads.

The final deployment, the C-3 system, would have deployed up to eight additional GBRs, several of them overseas, and the SBIRS-Low space-based missile tracking system. Additional GBIs would have been deployed in Alaska, along with a second interceptor site, likely in North Dakota, for a total of 250 GBI interceptors. This final phase, originally planned for deployment by as early as about 2010, was intended to be capable of defeating attacks by “many, complex” warheads.

Theater Missile Defenses

In addition to systems intended to defend against intercontinental-range ballistic missiles, over the last two decades the United States has developed and deployed a number of theater missile defense systems intended for defense of U.S. allies or U.S. forces overseas from shorter-range missiles. The current Missile Defense Agency (MDA) categorizes ballistic missiles by range as short-range (SRBM, less than 1,000 km), medium-range (MRBM, between 1,000 and 3,000 km), intermediate-range (IRBM, between 3,000 and 5,500 km), and intercontinental (ICBM, greater than 5,500 km).¹²

The development of such defenses was spurred by the experience of the 1991 Gulf War. During this war, Iraq fired about 88 Al-Hussein missiles at cities and military bases in Israel and Saudi Arabia. The

Al-Hussein was a modified Scud missile with a range of about 600 km, a small high-explosive warhead, and very poor accuracy (more than sev-eral kilometers).

The first of these TMD systems, the U.S. Army’s Patriot PAC-2 sys-tem, was just entering service at the time of the invasion of Kuwait in 1990. Its production was accelerated, and it was hastily deployed to Israel and Saudi Arabia in time to attempt to intercept 44 of the Iraqi missiles, the others landing too far away to be engaged. Patriot was

The first of these TMD systems, the U.S. Army’s Patriot PAC-2 sys-tem, was just entering service at the time of the invasion of Kuwait in 1990. Its production was accelerated, and it was hastily deployed to Israel and Saudi Arabia in time to attempt to intercept 44 of the Iraqi missiles, the others landing too far away to be engaged. Patriot was