Only two ABM systems have previously been operational against ICBMs, the U.S. Safeguard system, which utilized the LIM-49A Spartan and Sprint missiles, and the Russian A-35 anti-ballistic missile system which used the Galosh interceptor, each with a nuclear warhead themselves. Safeguard was only briefly operational; the Russian system has been improved and is still active, now called A-135 and using two missile types, Gorgon and Gazelle. However the U.S. Ground-Based Midcourse Defense (GMD, previously called NMD) system has recently reached initial operational capability. It does not have an explosive charge, but launches a .
Three shorter range tactical ABM systems are currently operational: the U.S. Army Patriot, U.S. Navy Aegis combat system/Standard SM-3, and the Israeli Arrow. The longer-range U.S. Terminal High Altitude Area Defense (THAAD) system is scheduled for deployment in 2009. In general short-range tactical ABMs cannot intercept ICBMs, even if within range. The tactical ABM radar and performance characteristics do not allow it, as an incoming ICBM warhead moves much faster than a tactical missile warhead. However it is possible the higher performance THAAD missile could be upgraded to intercept ICBMs.
Latest versions of the U.S. Hawk missile have a limited capability against tactical ballistic missiles, but is usually not described as an ABM. Similar claims have been made about the Russian long-range surface-to-air S-300 and S-400 series.
The American armed forces began experimenting with anti-missile missiles shortly after World War II, as the extent of German research into rocketry became clear. But defenses against Soviet long-range bombers took priority until the later 1950s, when the Soviets began to test their missiles (most notably via the Sputnik launch in October 1957). The first experimental ABM system was the soviet V-1000 system (part of the experimental "A-35" ABM programme), closely followed by Nike Zeus, a modification of then-existing air defense systems. Nike Zeus proved unworkable, and so work proceeded with Nike X.
Another avenue of research by the U.S. was the test explosions of several low yield nuclear weapons at very high altitudes over the southern Atlantic ocean, launched from ships. The devices used were the 1.7 kt boosted fission W25 warhead. When such an explosion takes place a burst of X-rays are released that strike the Earth's atmosphere, causing secondary showers of charged particles over an area hundreds of miles across. The movement of these charged particles in the Earth’s magnetic field causes a powerful EMP which induces very large currents in any conductive material. The purpose was to determine how much the EMP would interfere with radar tracking and other communications and the level of destruction of electronic circuitry aboard missiles and satellites. The project's results are not known, although similar so-called 'effects tests' were a regular feature of underground tests at the Nevada Test Site up to 1992. These 'effects tests' are used to determine how resistant specific warheads, RVs and other components are to exoatmospheric ABM bursts.
Other countries were also involved in early ABM research. A more advanced project was at CARDE in Canada, which researched the main problems of ABM systems. This included developing several advanced infrared detectors for terminal guidance, a number of missile airframe designs, a new and much more powerful solid rocket fuel, and numerous systems for testing it all. After a series of drastic budget cuts in the late 1950s the research wound down. One offshoot of the project was Gerald Bull’s system for inexpensive high-speed testing, consisting of missile airframes fired from a sabot round, which would later form the basis of Project HARP.
Nike X was a US system of two missiles, radars and their associated control systems. The original Nike Zeus (later called Spartan) was upgraded for longer range and a much larger 5 megatonne warhead intended to destroy warheads with a burst of x-rays outside the atmosphere. A second shorter-range missile called Sprint with very high acceleration was added to handle warheads that evaded longer-ranged Spartan. Sprint was a very fast missile (some sources claimed it accelerated to 8,000 mph (13 000 km/h) within 4 seconds of flight--an average acceleration of 100 g) and had a smaller W66 enhanced radiation warhead in the 1-3 kiloton range for in-atmosphere interceptions.
The new Spartan changed the deployment plans as well. Previously the Nike systems were to have been clustered near cities as a last-ditch defense, but the Spartan allowed for interceptions at hundreds of miles range. Therefore the basing changed to provide almost complete coverage of the United States in a system known as Sentinel. When this proved infeasible for economic reasons, a much smaller deployment using the same systems was proposed, Safeguard. Safeguard protected only the US ICBM fields from attack, theoretically ensuring that an attack could be responded to with a US launch, an example of the mutually assured destruction principle.
The only other ICBM ABM system to reach production was the Soviet A-35 system. It was initially a single-layer exoatmospheric (outside the atmosphere) design, using the Galosh (SH-01/ABM-1) interceptor. It was deployed at four sites around Moscow in the early 1970s.
Originally intended to be a larger deployment, the system was downsized to the two sites allowed under the 1972 ABM treaty. It was upgraded in the 1980s to a two-layer system, the A-135. The Gorgon (SH-11/ABM-4) long-range missile was designed to handle intercepts outside the atmosphere, and the Gazelle (SH-08/ABM-3) short-range missile endoatmospheric intercepts that eluded Gorgon. ABM-3 was considered to be technologically equivalent to the United States Safeguard system of the 1970s.
ABM systems were initially developed to counter single warheads launched from large Intercontinental ballistic missiles (ICBMs). The economics seemed simple enough; since rocket costs increase rapidly with size, the price of the ICBM launching a large warhead should always be greater than the much smaller interceptor missile needed to shoot it down. In an arms race the defense would always win.
Things changed dramatically with the introduction of Multiple independently targetable reentry vehicle (MIRV) warheads. Suddenly each launcher was throwing not one warhead, but several. The defense would still require a rocket for every warhead, as they would be re-entering over a wide space and could not be attacked by several warheads from a single antimissile rocket. Suddenly the defense was more expensive than offense; it was much less expensive to add more warheads, or even decoys, than it was to build the interceptor needed to shoot them down.
The experimental success of Nike X persuaded the Lyndon B. Johnson administration to propose a thin ABM defense. In a September 1967 speech, Defense Secretary Robert McNamara described it as Sentinel. McNamara, a private ABM opponent because of cost and feasibility (see cost-exchange ratio), claimed that Sentinel would be directed not against the Soviet Union's missiles (since the USSR had more than enough missiles to overwhelm any American defense), but rather against the potential nuclear threat of the People's Republic of China.
In the meantime a public debate over the merit of ABMs broke out. Even before the MIRV problem made ABM effectiveness non-workable in the late 1960s, some technical difficulties had already made an ABM system questionable for a large sophisticated attack. One problem was the Fractional Orbital Bombardment System (FOBS) that would give little warning to the defense. Another problem was high altitude EMP (whether from offensive or defensive nuclear warheads) which could degrade defensive radar systems.
Technical difficulties aside, the debate turned to an odd position: that no defense at all was better than any defense. Namely, a false sense of security might encourage ABM-defended nations to escalate against minor threats, believing they would be protected against any response. By this reasoning simply starting to deploy such a system could prompt a full-scale attack before it could become operational and thereby render such an attack useless. This curious set of arguments thus put the system in a terrible position: it couldn't possibly work, but if it did that would be even worse.
Under the ABM treaty and a 1974 revision, each country was allowed to deploy a single ABM system with only 100 interceptors to protect a single target. The Soviets deployed a system named A-35 (using Galosh interceptors), designed to protect Moscow. The U.S. deployed Safeguard (using Spartan/Sprint interceptors) to defend ballistic missile sites at Grand Forks Air Force Base, North Dakota, in 1975. The U.S. Safeguard system was only briefly operational. The Russian system (now called A-135) has been improved and is still active around Moscow.
On June 13, 2002, the United States withdrew from the Anti-Ballistic Missile Treaty and subsequently recommenced developing missile defense systems that would have formerly been prohibited by the bilateral treaty. This action was taken under the auspices of needing to defend against the possibility of a missile attack conducted by a rogue state.
SDI was an extremely ambitious program to provide a total shield against a massive Soviet ICBM attack. The initial concept envisioned large sophisticated orbiting laser battle stations, space-based relay mirrors, and nuclear-pumped X-ray laser satellites. Later research indicated that some planned technologies such as X-ray Lasers were not feasible with then-current technology. As research continued, SDI evolved through various concepts as designers struggled with the difficulty of such a large complex defense system. SDI remained a research program and was never deployed. However several SDI technologies were used in follow on ABM systems.
The Patriot antiaircraft missiles was the first deployed tactical ABM system, although it was not designed from the outset for that task and consequently had limitations. It was used in the 1991 Gulf War to attempt to intercept Iraqi Scud missiles. Post-war analyses show that the Patriot was much less effective than initially thought because of its radar and control system's inability to discriminate warheads from other objects when the Scud missiles broke up during reentry. On the other hand, the Scud itself was highly inaccurate and not very reliable. It was more a psychological than real threat to military targets.
Testing of ABMs and ABM technology continued through the 1990s with mixed success. However, following the Gulf War, improvements were made to several U.S. air defense systems. Patriot PAC-3 was developed and tested following the Gulf War. The PAC-3 is a complete redesign of the system deployed during the war, including a totally new missile. The improved guidance, radar and missile performance improves the probability of kill over the earlier PAC-2. In operation Iraqi Freedom, the initial claims that the Patriot PAC-3 had a near 100% success rate at intercepting short range tactical ballistic missiles (TBMs) was later revised to 70% in Saudi Arabia, and 40% in Israel. . However since no longer range Iraqi Scud missiles were fired, PAC-3 effectiveness against those was untested. Patriot was involved in three friendly fire incidents: two incidents of Patriot firings at coalition aircraft and one of U.S. aircraft firing on a Patriot battery.
From 1992 to 2000 a demonstration system for the US Army Terminal High Altitude Area Defense was deployed at White Sands Missile Range. Tests were conducted on a regular basis and resulted in early failures, but successful intercepts occurred in 1999. A new version of the Hawk missile was tested in the early to mid 90’s and by the end of 1998 the majority of US Marine Corps Hawk systems were modified to support basic theater anti-ballistic missile capabilities. Following the Gulf war, the Aegis combat system was expanded to include ABM capabilities. The Standard missile system was also enhanced and tested for ballistic missile interception. In the late 90’s SM-2 block IVA missiles were tested in a theater ballistic missile defense role. Standard Missile 3 (SM-3) systems have also been tested for an ABM role. In 2008 an SM-3 missile launched from a Ticonderoga-class cruiser, the USS Lake Erie, successfully intercepted a non-functioning satellite.
In 1998, Defense secretary William Cohen proposed spending an additional $6.6 billion on ballistic missile defense programs to build a system to protect against attacks from North Korea or accidental launches from Russia or China. The Israeli Arrow system was initially tested in 1990, before the first Gulf War. The Arrow was supported by the United States throughout the nineties.
The name Brilliant Pebbles comes from the small size of the satellite interceptors and great computational power enabling more autonomous targeting. Rather than rely exclusively on ground-based control, the many small interceptors would cooperatively communicate among themselves and target a large swarm of ICBM warheads in space or in the late boost phase. Development was later discontinued in favor of a limited ground-based defense.
In several tests, the U.S. military have demonstrated the feasibility of shooting down long and short range ballistic missiles. Combat effectiveness of newer systems against tactical ballistic missiles seems very high, as the Patriot PAC-3 had a 100% success rate in Operation Iraqi Freedom. However NMD real-world effectiveness against longer range ICBMs is less clear because they are much faster and a single warhead much harder to hit. Furthermore, warheads are likely to be accompanied by sophisticated penetration aids that are difficult to defeat.
While the Reagan era Strategic Defense Initiative was intended to shield against a massive Soviet attack, the current National Missile Defense has the more limited goal of shielding against a limited attack by a rogue state.
The Bush administration has accelerated development and deployment of a system proposed in 1998 by the Clinton administration. The system is a dual purpose test and interception facility in Alaska, and as of 2006 is operational with a few interceptor missiles. The Alaska site provides more protection against North Korean missiles or accidental launches from Russia or China, but is likely less effective against missiles launched from the Middle East. The Alaska interceptors may be later augmented by the naval Aegis Ballistic Missile Defense System, by ground-based missiles in other locations, or by the Boeing Airborne Laser. President Bush has referenced the September 11, 2001 Terrorist Attacks and the proliferation of ballistic missiles as reasons for missile defense.
Apart from the Moscow ABM deployment during the Cold War, Russia has actively striven for intrinsic ABM capabilities in its late model SAM systems. Russian ABM capable systems include the following:
The Arrow ABM system was designed and constructed in Israel with financial support by the United States in a multi-billion dollar development program called "Minhelet Homa" with the participation of companies like Israel Military Industries, Tadiran and Israel Aerospace Industries.
In 1998 the Israeli military conducted a successful test of their Arrow ABM. Designed to intercept incoming missiles travelling at up to 2 mile/s (3 km/s), the Arrow is expected to perform much better than the Patriot did in the Gulf War. On July 29, 2004 Israel and the United States carried out joint experiment in the USA, in which the Arrow was launched against a real Scud missile. The experiment was a success, as the Arrow destroyed the Scud with a direct hit. In December 2005 the system was successfully deployed in a test against a replicated Shahab-3 missile. This feat was repeated on February 11, 2007.