rocket and missile system

rocket and missile system


      any of a variety of weapons systems that deliver explosive warheads to their targets by means of rocket propulsion.

      Rocket is a general term used broadly to describe a variety of jet-propelled missiles (missile) in which forward motion results from reaction to the rearward ejection of matter (usually hot gases) at high velocity. The propulsive jet of gases usually consists of the combustion products of solid or liquid propellants.

      In a more restrictive sense, rocket propulsion is a unique member of the family of jet-propulsion engines that includes turbojet, pulse-jet, and ramjet systems. The rocket engine is different from these in that the elements of its propulsive jet (that is, the fuel and oxidizer) are self-contained within the vehicle. Therefore, the thrust produced is independent of the medium through which the vehicle travels, making the rocket engine capable of flight beyond the atmosphere or propulsion underwater. The turbojet, pulse-jet, and ramjet engines, on the other hand, carry only their fuel and depend on the oxygen content of the air for burning. For this reason, these varieties of jet engine are called air-breathing and are limited to operation within the Earth's atmosphere.

      For the purposes of this article, a rocket engine is a self-contained (i.e., non-air-breathing) propulsion system of the type described above, while the term rocket refers to any free-flight (unguided) missile of the types used since the beginning of rocketry. A guided missile is broadly any military missile that is capable of being guided or directed to a target after having been launched. Tactical guided missiles are shorter-ranged weapons designed for use in the immediate combat area. Long-range, or strategic, guided missiles are of two types, cruise and ballistic. Cruise missiles (cruise missile) are powered by air-breathing engines that provide almost continuous propulsion along a low, level flight path. A ballistic missile is propelled by a rocket engine for only the first part of its flight; for the rest of the flight the unpowered missile follows an arcing trajectory, small adjustments being made by its guidance mechanism. Strategic missiles usually carry nuclear warheads, while tactical missiles usually carry high explosives.

Military rockets

Early history
      There is no reliable early history of the “invention” of rockets. Most historians of rocketry trace the development to China, a land noted in ancient times for its fireworks displays. In 1232, when the Mongols laid siege to the city of K'ai-feng (Kaifeng), capital of Honan province, the Chinese defenders used weapons that were described as “arrows of flying fire.” There is no explicit statement that these arrows were rockets, but some students have concluded that they were because the record does not mention bows or other means of shooting the arrows. In the same battle, it is reported, the defenders dropped from the walls of the city a kind of bomb described as “heaven-shaking thunder.” From these meagre references some students have concluded that by 1232 the Chinese had discovered black powder (gunpowder) and had learned to use it to make explosive bombs as well as propulsive charges for rockets. Drawings made in military documents much later show powder rockets tied to arrows and spears. The propulsive jet evidently added to the range of these weapons and acted as an incendiary agent against targets.

      In the same century rockets appeared in Europe. There is indication that their first use was by the Mongols in the Battle of Legnica in 1241. The Arabs (Arab) are reported to have used rockets on the Iberian Peninsula in 1249; and in 1288 Valencia was attacked by rockets. In Italy, rockets are said to have been used by the Paduans (1379) and by the Venetians (1380).

      There are no details of the construction of these rockets, but they were presumably quite crude. The tubular rocket cases were probably many layers of tightly wrapped paper, coated with shellac. The propulsive charge was the basic black powder mixture of finely ground carbon (charcoal), potassium nitrate (saltpetre), and sulfur. The English scientist Roger Bacon (Bacon, Roger) wrote formulas for black powder about 1248 in his Epistola. In Germany a contemporary of Bacon, Albertus Magnus (Albertus Magnus, Saint), described powder charge formulas for rockets in his book De mirabilibus mundi. The first firearms appeared about 1325; they used a closed tube and black powder (now referred to as gunpowder) to propel a ball, somewhat erratically, over varying distances. Military engineers then began to invent and refine designs for both guns and rockets.

      By 1668, military rockets had increased in size and performance. In that year, a German colonel designed a rocket weighing 132 pounds (60 kilograms); it was constructed of wood and wrapped in glue-soaked sailcloth. It carried a gunpowder charge weighing 16 pounds. Nevertheless, the use of rockets seems to have waned, and for the nxt 100 years their employment in military campaigns appears to have been sporadic.

The 19th century
      A revival commenced late in the 18th century in India. There Hyder Ali, prince of Mysore, developed war rockets with an important change: the use of metal cylinders to contain the combustion powder. Although the hammered soft iron he used was crude, the bursting strength of the container of black powder was much higher than the earlier paper construction. Thus a greater internal pressure was possible, with a resultant greater thrust of the propulsive jet. The rocket body was lashed with leather thongs to a long bamboo stick. Range was perhaps up to three-quarters of a mile (more than a kilometre). Although individually these rockets were not accurate, dispersion error became less important when large numbers were fired rapidly in mass attacks. They were particularly effective against cavalry and were hurled into the air, after lighting, or skimmed along the hard dry ground. Hyder Ali's son, Tippu Sultan, continued to develop and expand the use of rocket weapons, reportedly increasing the number of rocket troops from 1,200 to a corps of 5,000. In battles at Seringapatam in 1792 and 1799 these rockets were used with considerable effect against the British.

      The news of the successful use of rockets spread through Europe. In England Sir William Congreve (Congreve, Sir William, 2nd Baronet) began to experiment privately. First, he experimented with a number of black-powder formulas and set down standard specifications of composition. He also standardized construction details and used improved production techniques. Also, his designs made it possible to choose either an explosive (ball charge) or incendiary warhead. The explosive warhead was separately ignited and could be timed by trimming the fuse length before launching. Thus, air bursts of the warheads were feasible at different ranges.

      Congreve's metal rocket bodies were equipped on one side with two or three thin metal loops into which a long guide stick was inserted and crimped firm. Weights of eight different sizes of these rockets ranged up to 60 pounds. Launching was from collapsible A-frame ladders. In addition to aerial bombardment, Congreve's rockets were often fired horizontally along the ground.

      These side-stick-mounted rockets were employed in a successful naval bombardment of the French coastal city of Boulogne in 1806. The next year a massed attack, using hundreds of rockets, burned most of Copenhagen to the ground. During the War of 1812 (1812, War of) between the United States and the British, rockets were employed on numerous occasions. The two best-known engagements occurred in 1814. At the Battle of Bladensburg (August 24) the use of rockets assisted British forces to turn the flank of the American troops defending Washington, D.C. As a result, the British were able to capture the city. In September the British forces attempted to capture Fort McHenry, which guarded Baltimore harbour. Rockets were fired from a specially designed ship, the Erebus, and from small boats. The British were unsuccessful in their bombardment, but on that occasion Francis Scott Key (Key, Francis Scott), inspired by the sight of the night engagement, wrote “The Star Spangled Banner,” later adopted as the United States national anthem. “The rockets' red glare” has continued to memorialize Congreve's rockets ever since.

      In 1815 Congreve further improved his designs by mounting his guide stick along the central axis. The rocket's propulsive jet issued through five equally spaced holes rather than a single orifice. The forward portion of the guide stick, which screwed into the rocket, was sheathed with brass to prevent burning. The centre-stick-mounted rockets were significantly more accurate. Also, their design permitted launching from thin copper tubes.

      Maximum ranges of Congreve rockets were from one-half mile to two miles (0.8 to 3.2 kilometres), depending upon size. They were competitive in performance and cost with the ponderous 10-inch mortar and were vastly more mobile.

      The next significant development in rocketry occurred about the middle of the 19th century. William Hale, a British engineer, invented a method of successfully eliminating the deadweight of the flight-stabilizing guide stick. By designing jet vents at an angle, he was able to spin the rocket. He developed various designs, including curved vanes that were acted upon by the rocket jet. These rockets, stabilized by means of spin, represented a major improvement in performance and ease of handling.

      Even the new rockets, however, could not compete with the greatly improved artillery with rifled bores. The rocket corps of most European armies were dissolved, though rockets were still used in swampy or mountainous areas that were difficult for the much heavier mortars and guns. The Austrian Rocket Corps, using Hale rockets, won a number of engagements in mountainous terrain in Hungary and Italy. Other successful uses were by the Dutch (Netherlands, The) colonial services in Celebes and by Russia in a number of engagements in the Turkistan War.

      Hale sold his patent rights to the United States in time for some 2,000 rockets to be made for the Mexican War (Mexican-American War), 1846–48. Although some were fired, they were not particularly successful. Rockets were used in a limited way in the American Civil War (1861–65), but reports are fragmentary, and apparently they were not decisive. The U.S. Ordnance Manual of 1862 lists 16-pound Hale rockets with a range of 1.25 miles.

      In Sweden about the turn of the century, Wilhelm Unge invented a device described as an “aerial torpedo.” Based upon the stickless Hale rocket, it incorporated a number of design improvements. One of these was a rocket motor nozzle that caused the gas flow to converge and then diverge. Another was the use of smokeless powder based on nitroglycerin. Unge believed that his aerial torpedoes would be valuable as surface-to-air weapons against dirigibles. Velocity and range were increased, and about 1909 the Krupp armament firm of Germany purchased the patents and a number of rockets for further experimentation.

World War I and after
      In the United States, meanwhile, Robert Hutchings Goddard (Goddard, Robert Hutchings) was conducting theoretical and experimental research on rocket motors at Worcester, Mass. Using a steel motor with a tapered nozzle, he achieved greatly improved thrust and efficiency. During World War I Goddard developed a number of designs of small military rockets to be launched from a lightweight hand launcher. By switching from black powder to double-base powder (40 percent nitroglycerin, 60 percent nitrocellulose), a far more potent propulsion charge was obtained. These rockets were proving successful under tests by the U.S. Army when the Armistice was signed; they became the forerunners of the bazooka of World War II.

      World War I actually saw little use of rocket weapons, despite successful French incendiary antiballoon rockets and a German trench-war technique by which a grappling hook was thrown over enemy barbed wire by a rocket with a line attached.

      Many researchers besides Goddard used the wartime interest in rockets to push experimentation, the most noteworthy being Elmer Sperry (Sperry, Elmer Ambrose) and his son, Lawrence, in the United States. The Sperrys worked on a concept of an “aerial torpedo,” a pilotless airplane, carrying an explosive charge, that would utilize gyroscopic, automatic control to fly to a preselected target. Numerous flight attempts were made in 1917, some successful. Because of early interest in military use, the U.S. Army Signal Corps organized a separate program under Charles F. Kettering (Kettering, Charles F.) in Dayton, Ohio, late in 1918. The Kettering design used a gyroscope for lateral control to a preset direction and an aneroid barometer for pitch (fore and aft) control to maintain a preset altitude. A high angle of dihedral (upward tilt) in the biplane wings provided stability about the roll axis. The aircraft was rail-launched. Distance to target was determined by the number of revolutions of a propeller. When the predetermined number of revolutions had occurred, the wings of the airplane were dropped off and the aircraft carrying the bomb load dropped on the target.

      The limited time available to attack the formidable design problems of these systems doomed the programs, and they never became operational.

      As World War II approached, minor and varied experimental and research activities on rockets and guided missiles were underway in a number of countries. But in Germany, under great secrecy, the effort was concentrated. Successful flights as high as one mile were made in 1931–32 with gasoline–oxygen-powered rockets by the German Rocket Society. Funds for such amateur activities were scarce, and the society sought support from the German army. The work of Wernher von Braun (Braun, Wernher von), a member of the society, attracted the attention of Captain Walter R. Dornberger (Dornberger, Walter Robert). Von Braun became the technical leader of a small group developing liquid-propellant rockets for the German army. By 1937 the Dornberger–Braun team, expanded to hundreds of scientists, engineers, and technicians, moved its operations from Kummersdorf to Peenemünde, a deserted area on the Baltic coast. Here the technology for a long-range ballistic missile was developed and tested (see below Strategic missiles (rocket and missile system)).

      World War II saw the expenditure of immense resources and talent for the development of rocket-propelled weapons.

Barrage rockets
      The Germans began the war with a lead in this category of weapon, and their 150-millimetre and 210-millimetre bombardment rockets were highly effective. These were fired from a variety of towed and vehicle-mounted multitube launchers, from launching rails on the sides of armoured personnel carriers, and, for massive bombardments, even from their packing crates. Mobile German rocket batteries were able to lay down heavy and unexpected concentrations of fire on Allied positions. The 150-millimetre Nebelwerfer, a towed, six-tube launcher, was particularly respected by U.S. and British troops, to whom it was known as the “Screaming Meemie” or “Moaning Minnie” for the eerie sound made by the incoming rockets. Maximum range was more than 6,000 yards (5,500 metres).

      A five-inch rocket with an explosive warhead was developed in Great Britain. Its range was two to three miles. These rockets, fired from specially equipped naval vessels, were used in heavy coastal bombardment prior to landings in the Mediterranean. Firing rates were 800–1,000 in less than 45 seconds from each ship.

      A development of the U.S. Army was the Calliope, a 60-tube launching projector for 4.5-inch rockets mounted on a Sherman tank. The launcher was mounted on the tank's gun turret, and both azimuth (horizontal direction) and elevation were controllable. Rockets were fired in rapid succession (ripple-fired) to keep the rockets from interfering with one another as they would in salvo firing.

 Other conventional rockets developed in the United States included a 4.5-inch barrage rocket with a range of 1,100 yards and a five-inch rocket of longer range. The latter was used extensively in the Pacific theatre of war, fired from launching barges against shore installations, particularly just before landing operations (see photograph—>). The firing rate of these flat-bottom boats was 500 per minute. Other rockets were used for smoke laying and demolition. The United States produced more than four million of the 4.5-inch rockets and 15 million of the smaller bazooka rockets during the war.

      As far as is known, Soviet (Union of Soviet Socialist Republics) rocket development during World War II was limited. Extensive use was made of barrage, ripple-fired rockets. Both A-frame and truck-mounted launchers were used. The Soviets mass-produced a 130-millimetre rocket known as the Katyusha. From 16 to 48 Katyushas were fired from a boxlike launcher known as the Stalin Organ, mounted on a gun carriage.

      Beginning in mid-1940, Clarence N. Hickman, who had worked with Robert Goddard during World War I, supervised the development of a refined design of the hand-launched rocket. The new rocket, about 20 inches (50 centimetres) long, 2.36 inches in diameter, and weighing 3.5 pounds, was fired from a steel tube that became popularly known as the bazooka. Designed chiefly for use against tanks and fortified positions at short ranges (up to 600 yards), the bazooka surprised the Germans when it was first used in the North African landings of 1942. Although the rocket traveled slowly, it carried a potent shaped-charge warhead that gave infantrymen the striking power of light artillery.

      The German counterpart of the bazooka was a light 88-millimetre rocket launcher known as Panzerschreck (“Tank Terror”) or Ofenrohr (“Stovepipe”).

Antiaircraft rockets
      During World War II high-altitude bombing above the range of antiaircraft guns (antiaircraft gun) necessitated the development of rocket-powered weapons.

      In Great Britain, initial effort was aimed at achieving the equivalent destructive power of the three-inch and later the 3.7-inch antiaircraft gun. Two important innovations were introduced by the British in connection with the three-inch rocket. One was a rocket-propelled aerial-defense system. A parachute and wire device was rocketed aloft, trailing a wire that unwound at high speed from a bobbin on the ground with the object of snagging the aircraft's propellers or shearing off the wings. Altitudes as high as 20,000 feet were attained. The other device was a type of proximity fuze using a photoelectric cell and thermionic amplifier. A change in light intensity on the photocell caused by light reflected from a nearby airplane (projected on the cell by means of a lens) triggered the explosive shell.

      The only significant antiaircraft rocket development by the Germans was the Taifun. A slender, six-foot, liquid-propellant rocket of simple concept, the Taifun was intended for altitudes of 50,000 feet. The design embodied coaxial tankage of nitric acid and a mixture of organic fuels, but the weapon never became operational.

Aerial rockets
      Britain, Germany, the Soviet Union, Japan, and the United States all developed airborne rockets for use against surface as well as aerial targets. These were almost invariably fin-stabilized because of the effective aerodynamic forces when launched at speeds of 250 miles per hour and more. Tube launchers were used at first, but later straight-rail or zero-length launchers, located under the wings of the airplane, were employed.

      One of the most successful of the German rockets was the 50-millimetre R4M. The tail fins remained folded until launch, facilitating close loading arrangements.

      The U.S. achieved great success with a 4.5-inch rocket, three or four of which were carried under each wing of Allied fighter planes. These rockets were highly effective against motor columns, tanks, troop and supply trains, fuel and ammunition depots, airfields, and barges.

      A variation on the airborne rocket was the addition of rocket motors and fins to conventional bombs. This had the effect of flattening the trajectory, extending the range, and increasing velocity at impact, useful against concrete bunkers and hardened targets. These weapons were called glide bombs, and the Japanese had 100-kilogram and 370-kilogram (225-pound and 815-pound) versions. The Soviet Union employed 25- and 100-kilogram versions, launched from the IL-2 Stormovik attack aircraft.

      After World War II, unguided, folding-fin rockets fired from multiple-tube pods became a standard air-to-ground munition for ground-attack aircraft and helicopter gunships. Though not as accurate as guided missiles or gun systems, they could saturate concentrations of troops or vehicles with a lethal volume of fire. Many ground forces continued to field truck-mounted, tube-launched rockets that could be fired simultaneously in salvos or ripple-fired in rapid succession. Such artillery rocket systems, or multiple-launch rocket systems, generally fired rockets of 100 to 150 millimetres in diameter and had ranges of 12 to 18 miles. The rockets carried a variety of warheads, including high explosive, antipersonnel, incendiary, smoke, and chemical.

      The Soviet Union and the United States built unguided ballistic rockets for about 30 years after the war. In 1955 the U.S. Army began deployment of the Honest John in western Europe, and from 1957 the Soviet Union built a series of large, spin-stabilized rockets, launched from mobile transporters, given the NATO designation FROG (free rocket over ground). These missiles, from 25 to 30 feet long and two to three feet in diameter, had ranges of 20 to 45 miles and could be nuclear-armed. Egypt and Syria fired many FROG missiles during the opening salvos of the Arab–Israeli War of October 1973, as did Iraq in its war with Iran in the 1980s, but in the 1970s large rockets were phased out of the superpowers' front line in favour of inertially guided missiles such as the U.S. Lance and the Soviet SS-21 Scarab.

Frederick C. Durant III Ed.

Tactical guided missiles
      Guided missiles (guided missile) were a product of post-World War II developments in electronics, computers, sensors, avionics, and, to only a slightly lesser degree, rocket and turbojet propulsion and aerodynamics. Although tactical, or battlefield, guided missiles were designed to perform many different roles, they were bound together as a class of weapon by similarities in sensor, guidance, and control systems. Control over a missile's direction was most commonly achieved by the deflection of aerodynamic surfaces such as tail fins; reaction jets or rockets and thrust-vectoring were also employed. But it was in their guidance systems that these missiles gained their distinction, since the ability to make down-course corrections in order to seek or “home” onto a target separated guided missiles from purely ballistic weapons such as free-flight rockets and artillery shells.

Guidance methods
      The earliest guided missiles used simple command guidance, but within 20 years of World War II virtually all guidance systems contained autopilots (automatic pilot) or autostabilization systems, frequently in combination with memory circuits and sophisticated navigation sensors and computers (computer). Five basic guidance methods came to be used, either alone or in combination: command, inertial, active, semiactive, and passive.

      Command guidance involved tracking the projectile from the launch site or platform and transmitting commands by radio, radar, or laser impulses or along thin wires or optical fibres. Tracking might be accomplished by radar or optical instruments from the launch site or by radar or television imagery relayed from the missile. The earliest command-guided air-to-surface and antitank munitions were tracked by eye and controlled by hand; later the naked eye gave way to enhanced optics and television tracking, which often operated in the infrared range and issued commands generated automatically by computerized fire-control systems. Another early command guidance method was beam riding, in which the missile sensed a radar beam pointed at the target and automatically corrected back to it. laser beams were later used for the same purpose. Also using a form of command guidance were television-guided (television) missiles, in which a small television camera mounted in the nose of the weapon beamed a picture of the target back to an operator who sent commands to keep the target centred in the tracking screen until impact. A form of command guidance used from the 1980s by the U.S. Patriot surface-to-air system was called track-via-missile. In this system a radar unit in the missile tracked the target and transmitted relative bearing and velocity information to the launch site, where control systems computed the optimal trajectory for intercepting the target and sent appropriate commands back to the missile.

      Inertial guidance was installed in long-range ballistic missiles in the 1950s, but, with advances in miniaturized circuitry, microcomputers, and inertial sensors, it became common in tactical weapons after the 1970s. Inertial systems involved the use of small, highly accurate gyroscopic (gyroscope) platforms to continuously determine the position of the missile in space. These provided inputs to guidance computers, which used the position information in addition to inputs from accelerometers or integrating circuits to calculate velocity and direction. The guidance computer, which was programmed with the desired flight path, then generated commands to maintain the course.

      An advantage of inertial guidance was that it required no electronic emissions from the missile or launch platform that could be picked up by the enemy. Many antiship missiles and some long-range air-to-air missiles, therefore, used inertial guidance to reach the general vicinity of their targets and then active radar guidance for terminal homing. Passive-homing antiradiation missiles, designed to destroy radar installations, generally combined inertial guidance with memory-equipped autopilots to maintain their trajectory toward the target in case the radar stopped transmitting.

      With active guidance, the missile would track its target by means of emissions that it generated itself. Active guidance was commonly used for terminal homing. Examples were antiship, surface-to-air, and air-to-air missiles that used self-contained radar systems to track their targets. Active guidance had the disadvantage of depending on emissions that could be tracked, jammed, or tricked by decoys.

      Semiactive guidance involved illuminating or designating the target with energy emitted from a source other than the missile; a seeker in the projectile that was sensitive to the reflected energy then homed onto the target. Like active guidance, semiactive guidance was commonly used for terminal homing. In the U.S. Hawk and Soviet SA-6 Gainful antiaircraft systems, for example, the missile homed in on radar emissions transmitted from the launch site and reflected off the target, measuring the Doppler shift in the reflected emissions to assist in computing the intercept trajectory. (SA-6 Gainful is a designation given by NATO to the Soviet missile system. In this section, missile systems and aircraft of the former Soviet Union are referred to by their NATO designations.) The AIM-7 Sparrow air-to-air missile of the U.S. Air Force used a similar semiactive radar guidance method. Laser-guided missiles also could use semiactive methods by illuminating the target with a small spot of laser light and homing onto that precise light frequency through a seeker head in the missile.

      With semiactive homing the designator or illuminator might be remote from the launch platform. The U.S. Hellfire antitank missile, for example, used laser designation by an air or ground observer who could be situated many miles from the launching helicopter.

      Passive guidance systems neither emitted energy nor received commands from an external source; rather, they “locked” onto an electronic emission coming from the target itself. The earliest successful passive homing munitions were “heat-seeking” air-to-air missiles that homed onto the infrared emissions of jet engine exhausts. The first such missile to achieve wide success was the AIM-9 Sidewinder developed by the U.S. Navy in the 1950s. Many later passive homing air-to-air missiles homed onto ultraviolet radiation as well, using on-board guidance computers and accelerometers to compute optimal intercept trajectories. Among the most advanced passive homing systems were optically tracking munitions that could “see” a visual or infrared image in much the same way as the human eye does, memorize it by means of computer logic, and home onto it. Many passive homing systems required target identification and lock-on by a human operator prior to launch. With infrared antiaircraft missiles, a successful lock-on was indicated by an audible tone in the pilot's or operator's headset; with television or imaging infrared systems, the operator or pilot acquired the target on a screen, which relayed data from the missile's seeker head, and then locked on manually.

      Passive guidance systems benefited enormously from a miniaturization of electronic components and from advances in seeker-head technology. Small, heat-seeking, shoulder-fired antiaircraft missiles first became a major factor in land warfare during the final stages of the Vietnam War, with the Soviet SA-7 Grail playing a major role in neutralizing the South Vietnamese Air Force in the final communist offensive in 1975. Ten years later the U.S. Stinger and British Blowpipe proved effective against Soviet aircraft and helicopters in Afghanistan, as did the U.S. Redeye in Central America.

Guided-missile systems
      The principal categories of tactical guided missiles are antitank and assault, air-to-surface, air-to-air, antiship, and surface-to-air. Distinctions between these categories were not always clear, the launching of both antitank and infantry antiaircraft missiles from helicopters being a case in point.

Antitank (antitank weapon) and guided assault
      One of the most important categories of guided missile to emerge after World War II was the antitank, or antiarmour, missile. The guided assault missile, for use against bunkers and structures, was closely related. A logical extension of unguided infantry antitank weapons carrying shaped-charge warheads for penetrating armour, guided antitank missiles acquired considerably more range and power than their shoulder-fired predecessors. While originally intended for issue to infantry formations for self-protection, the tactical flexibility and utility of guided antitank missiles led to their installation on light trucks, on armoured personnel carriers, and, most important, on antitank helicopters.

      The first guided antitank missiles were controlled by electronic commands transmitted along extremely thin wires played out from a spool on the rear of the missile. Propelled by solid-fuel sustainer rockets, these missiles used aerodynamic fins for lift and control. Tracking was visual, by means of a flare in the missile's tail, and guidance commands were generated by a hand-operated joystick. In operating these missiles, the gunner simply superimposed the tracking flare on the target and waited for impact. The missiles were typically designed to be fired from their carrying containers, with the total package small enough to be carried by one or two men. Germany was developing weapons of this kind at the end of World War II and may have fired some in battle.

      After the war French engineers adapted the German technology and developed the SS-10/SS-11 family of missiles. The SS-11 was adopted by the United States as an interim helicopter-fired antitank missile pending the development of the TOW (for tube-launched, optically tracked, wire-guided) missile. Because it was designed for greater range and hitting power, TOW was mounted primarily on vehicles and, particularly, on attack helicopters (helicopter). Helicopter-fired antitank missiles were first used in combat when the U.S. Army deployed several TOW-equipped UH-1 “Hueys” to Vietnam in response to the 1972 communist Easter offensive. TOW was the principal U.S. antiarmour munition until Hellfire, a more sophisticated helicopter-fired missile with semiactive laser and passive infrared homing, was mounted on the Hughes AH-64 Apache attack helicopter in the 1980s.

      The British Swingfire and the French-designed, internationally marketed MILAN (missile d'infanterie léger antichar, or “light infantry antitank missile”) and HOT (haut subsonique optiquement téléguidé tiré d'un tube, or “high-subsonic, optically teleguided, tube-fired”) were similar in concept and capability to TOW.

      The Soviets developed an entire family of antitank guided missiles beginning with the AT-1 Snapper, the AT-2 Swatter, and the AT-3 Sagger. The Sagger, a relatively small missile designed for infantry use on the lines of the original German concept, saw use in Vietnam and was used with conspicuous success by Egyptian infantry in the Suez Canal crossing of the 1973 Arab-Israeli War. The AT-6 Spiral, a Soviet version of TOW and Hellfire, became the principal antiarmour munition of Soviet attack helicopters.

      Many antitank missile systems of later generations transmitted guidance commands by radio rather than by wire, and semiactive laser designation and passive infrared homing also became common. Guidance and control methods were more sophisticated than the original visual tracking and manual commands. TOW, for example, required the gunner simply to centre the reticle of his optical sight on the target, and the missile was tracked and guided automatically. Extremely thin optical fibres began to replace wires as a guidance link in the 1980s.

      The United States began to deploy tactical air-to-surface guided missiles as a standard aerial munition in the late 1950s. The first of these was the AGM-12 (for aerial guided munition) Bullpup, a rocket-powered weapon that employed visual tracking and radio-transmitted command guidance. The pilot controlled the missile by means of a small side-mounted joystick and guided it toward the target by observing a small flare in its tail. Though Bullpup was simple and accurate, the delivery aircraft had to continue flying toward the target until the weapon struck—a vulnerable maneuver. The 250-pound (115-kilogram) warhead on the initial version of Bullpup proved inadequate for “hard” targets such as reinforced concrete bridges in Vietnam, and later versions had a 1,000-pound warhead. The rocket-powered AGM-45 Shrike antiradiation missile was used in Vietnam to attack enemy radar and surface-to-air sites by passively homing onto their radar emissions. The first missile of its kind used in combat, the Shrike had to be tuned to the desired radar frequency before flight. Because it had no memory circuits and required continuous emissions for homing, it could be defeated by simply turning off the target radar. Following the Shrike was the AGM-78 Standard ARM (antiradiation munition), a larger and more expensive weapon that incorporated memory circuits and could be tuned to any of several frequencies in flight. Also rocket-propelled, it had a range of about 35 miles (55 kilometres). Faster and more sophisticated still was the AGM-88 HARM (high-speed antiradiation missile), introduced into service in 1983.

      Replacing the Bullpup as an optically tracked missile was the AGM-64/65 Maverick family of rocket-powered missiles. Early versions used television tracking, while later versions employed infrared, permitting the fixing of targets at longer ranges and at night. The self-contained guidance system incorporated computer logic that enabled the missile to lock onto an image of the target once the operator had identified it on his cockpit television monitor. Warheads varied from a 125-pound shaped charge for use against armour to high-explosive blast charges of 300 pounds.

      Though less was known about them, the Soviets fielded an extensive array of air-to-surface missiles equivalent to the Bullpup and Maverick and to the Hellfire antitank missile. Notable among these was the radio-command-guided AS-7 Kerry, the antiradar AS-8 and AS-9, and the television-guided AS-10 Karen and AS-14 Kedge (the last with a range of about 25 miles). These missiles were fired from tactical fighters such as the MiG-27 Flogger and attack helicopters such as the Mi-24 Hind and Mi-28 Havoc.

      Developed in 1947, the radar-guided, subsonic Firebird was the first U.S. guided air-to-air missile. It was rendered obsolete within a few years by supersonic missiles such as the AIM-4 (for air-intercept missile) Falcon, the AIM-9 Sidewinder, and the AIM-7 Sparrow. The widely imitated Sidewinder was particularly influential. Early versions, which homed onto the infrared emissions from jet engine tailpipes, could approach only from the target's rear quadrants. Later versions, beginning with the AIM-9L, were fitted with more sophisticated seekers sensitive to a broader spectrum of radiation. These gave the missile the capability of sensing exhaust emissions from the side or front of the target aircraft. Driven by the requirements of supersonic combat during the 1960s, the ranges of such missiles as the Sidewinder increased from about two miles to 10–15 miles. The AIM-54 Phoenix, a semiactive radar missile with active radar terminal homing introduced by the U.S. Navy in 1974, was capable of ranges in excess of 100 miles. Fired from the F-14 Tomcat, it was controlled by an acquisition, tracking, and guidance system that could engage up to six targets simultaneously. Combat experience in Southeast Asia and the Middle East produced increased tactical sophistication, so that fighter aircraft were routinely armed with several kinds of missile to deal with a variety of situations. U.S. carrier-based fighters, for instance, carried both heat-seeking Sidewinders and radar-homing Sparrows. Meanwhile, the Europeans developed such infrared-homing missiles as the British Red Top and the French Magic, the latter being a short-range (one-quarter to four miles) highly maneuverable equivalent of the Sidewinder.

      The Soviets fielded an extended series of air-to-air missiles, beginning in the 1960s with the AA-1 Alkali, a relatively primitive semiactive radar missile, the AA-2 Atoll, an infrared missile closely modeled after the Sidewinder, and the AA-3 Anab, a long-range, semiactive radar-homing missile carried by air-defense fighters. The AA-5 Ash was a large, medium-range radar-guided missile, while the AA-6 Acrid was similar to the Anab but larger and with greater range. The AA-7 Apex, a Sparrow equivalent, and the AA-8 Aphid, a relatively small missile for close-in use, were introduced during the 1970s. Both used semiactive radar guidance, though the Aphid was apparently produced in an infrared-homing version as well. The long-range, semiactive radar-guided AA-9 Amos appeared in the mid-1980s; it was associated with the MiG-31 Foxhound interceptor, much as the U.S. Phoenix was associated with the F-14. The Foxhound/Amos combination may have been fitted with a look-down/shoot-down capability, enabling it to engage low-flying targets while looking downward against a cluttered radar background. The AA-10 Alamo, a medium-range missile similar to the Amos, apparently had passive radar guidance designed to home onto carrier-wave emissions from U.S. aircraft firing the semiactive radar-homing Sparrow. The AA-11 Archer was a short-range missile used in combination with the Amos and Alamo.

      Improvements in air-to-air missiles included the combined use of several methods of guidance for greater flexibility and lethality. Active radar or infrared terminal homing, for example, were often used with semiactive radar guidance in midcourse. Also, passive radar homing, which became an important means of air-to-air guidance, was backed up by inertial guidance for mid-course and by an alternate terminal homing method in case the target aircraft shut off its radar. Sophisticated optical and laser proximity fuzes became common; these were used with directional warheads that focused their blast effects toward the target. Tactical demands combined with advancing technology to channel the development of air-to-air missiles into three increasingly specialized categories: large, highly sophisticated long-range air-intercept missiles, such as the Phoenix and Amos, capable of ranges from 40 to 125 miles; short-range, highly maneuverable (and less expensive) “dogfighter” missiles with maximum ranges of six to nine miles; and medium-range missiles, mostly using semiactive radar homing, with maximum ranges of 20 to 25 miles. Representative of the third category was the AIM-120 AMRAAM (for advanced medium-range air-to-air missile), jointly developed by the U.S. Air Force and Navy for use with NATO aircraft. AMRAAM combined inertial mid-course guidance with active radar homing.

      Despite their different methods of delivery, antiship missiles formed a coherent class largely because they were designed to penetrate the heavy defenses of warships.

      The Hs-293 missiles developed by Germany during World War II were the first guided antiship missiles. Though accurate, they required the delivery aircraft to stay on the same line of sight as the weapon and target; the resultant flight paths were predictable and highly vulnerable, and the Allies quickly developed effective defenses.

      Partly because Britain and the United States relied on carrier-based aircraft armed with conventional torpedoes, bombs, and unguided rockets to attack naval targets, antiship missiles at first received little emphasis in the West after the war. The Soviets, however, saw antiship missiles as a counter to Western naval superiority and developed an extensive range of air- and surface-launched antiship missiles, beginning with the AS-1 Kennel. The destruction of an Israeli destroyer by two SS-N-2 Styx missiles fired by Soviet-supplied Egyptian missile boats in October 1967 demonstrated the effectiveness of the Soviet systems, and the Western powers developed their own guided missiles. The resultant systems began entering service in the 1970s and first saw combat in 1982, during the Falkland Islands War. In that conflict the British Sea Skua, a small, rocket-powered, sea-skimming missile with semiactive radar homing, weighing about 325 pounds, was fired successfully from helicopters, while the Argentines sank a destroyer and a containership and damaged another destroyer with the solid-rocket-powered, active radar-homing French Exocet, fired from both aircraft and ground launchers. The Exocet weighed about 1,500 pounds and had an effective range of 35 to 40 miles.

      The Exocet was one of a number of Western antiship missiles of the same general kind. Guidance was mostly by active radar, often supplemented in mid-course by inertial autopilots and in terminal flight by passive radar and infrared homing. Although designed for use from carrier-based attack aircraft, missiles of this sort were also carried by bombers and coastal patrol aircraft and were mounted on ship- and land-based launchers. The most important U.S. antiship missile was the turbojet-powered Harpoon, which weighed about 1,200 pounds in its air-launched version and had a 420-pound warhead. Employing both active and passive radar homing, this missile could be programmed for sea-skimming attack or a “pop-up and dive” maneuver to evade a ship's close-in defense systems. The turbojet-powered British Sea Eagle weighed somewhat more than the Harpoon and employed active radar homing. The West German Kormoran was also an air-launched missile. The Norwegian Penguin, a rocket-powered missile weighing between 700 and 820 pounds and employing technology derived from the U.S. Maverick air-to-surface missile, had a range of about 17 miles and supplemented its active radar guidance with passive infrared homing. The Penguin was exported widely for fighter-bomber, attack boat, and helicopter use. The Israeli Gabriel, a 1,325-pound missile with a 330-pound warhead launched from both aircraft and ships, employed active radar homing and had a range of 20 miles.

      The U.S. Navy Tomahawk defined a separate category of antiship missile: it was a long-range, turbofan-powered cruise missile first developed as a strategic nuclear delivery system (see below Strategic missiles). Tomahawk was carried by surface vessels and submarines in both ground-attack and antiship versions. The antiship version, equipped with a modified Harpoon guidance system, had a range of 275 miles. Only 20 feet long and 20.5 inches (53 centimetres) in diameter, the Tomahawk was fired from its launch tubes by a solid-fueled booster and cruised at subsonic speeds on flip-out wings.

      For short-range antiship warfare, the Soviet Union deployed its AS series, 7, 8, 9, 10, and 14 air-to-surface missiles. Long-range antiship missiles designed for use from bomber and patrol aircraft included the 50-foot, swept-wing AS-3 Kangaroo, introduced in 1961 with a range exceeding 400 miles. The AS-4 Kitchen, a Mach-2 (twice the speed of sound) rocket-powered missile with a range of about 250 miles, also was introduced in 1961, and the liquid-fuel, rocket-powered Mach-1.5 AS-5 Kelt was first deployed in 1966. The Mach-3 AS-6 Kingfish, introduced in 1970, could travel 250 miles.

      Ship-based Soviet systems included the SS-N-2 Styx, a subsonic aerodynamic missile first deployed in 1959–60 with a range of 25 miles, and the SS-N-3 Shaddock, a much larger system resembling a swept-wing fighter aircraft with a range of 280 miles. The SS-N-12 Sandbox, introduced in the 1970s on the Kiev-class antisubmarine carriers, was apparently an improved Shaddock. The SS-N-19 Shipwreck, a small, vertically launched, flip-out wing supersonic missile with a range of about 390 miles, appeared in the 1980s.

      To defend against antiship missiles, navies employed towed or helicopter-borne decoys. Sometimes chaff (strips of foil or clusters of fine glass or wire) would be released in the air to create false radar targets. Defenses included long-range chaff rockets to mask a vessel from the radar of distant ships, close-in quick-blooming chaff flares to confuse active radar homers on missiles, and radar jamming to defeat acquisition and tracking radars and confuse missile seeker systems. For close-in defense, combatant ships were fitted with high-performance, short-range missiles such as the British Seawolf and automatic gun systems such as the U.S. 20-millimetre Phalanx. Advances in missile-defense systems had to keep up with the natural affinity of antiship missiles for stealth technology: the visual and infrared signatures and radar cross sections of Western antiship missiles became so small that relatively minor modifications in shape and modest applications of radar-absorptive materials could make them difficult to detect with radar and electro-optical systems, except at short ranges.

      Guided surface-to-air missiles, or SAMs, were under development when World War II ended, notably by the Germans, but were not sufficiently perfected to be used in combat. This changed in the 1950s and '60s with the rapid development of sophisticated SAM systems in the Soviet Union, the United States, Great Britain, and France. With other industrialized nations following suit, surface-to-air missiles of indigenous design, particularly in the smaller categories, were fielded by many armies and navies.

      The Soviet Union committed more technical and fiscal resources to the development of guided-missile air-defense systems than any other nation. Beginning with the SA-1 Guild, developed in the immediate postwar period, the Soviets steadily fielded SAMs of growing sophistication. These fell into two categories: systems such as the Guild, the SA-3 Goa, the SA-5 Gammon, and the SA-10 Grumble, which were deployed in defense of fixed installations; and mobile tactical systems capable of accompanying land forces. Most of the tactical systems had naval versions. The SA-2 Guideline, introduced in 1958, was the most widely deployed of the early SAMs and was the first surface-to-air guided-missile system used in combat. This two-stage missile with a solid booster and a liquid-propellant (kerosene and nitric acid) sustainer, could engage targets at ranges of 28 miles and as high as 60,000 feet. Equipped with an array of van-mounted radars for target acquisition and tracking and for missile tracking and command guidance, Guideline proved effective in Vietnam. With adequate warning, U.S. fighters could outmaneuver the relatively large missiles, called “flying telephone poles” by pilots, and electronic countermeasures (ECM) reduced the effectiveness of the tracking radars; but, while these SAMs inflicted relatively few losses, they forced U.S. aircraft down to low altitudes, where antiaircraft artillery and small arms exacted a heavy toll. Later versions of the SA-2 were equipped with optical tracking to counter the effects of ECM; this became a standard feature on SAM systems. After retirement from first-line Soviet service, the SA-2 remained in use in the Third World.

      The SA-3 Goa, derived from the Guideline but modified for use against low-altitude targets, was first deployed in 1963—primarily in defense of fixed installations. The SA-N-1 was a similar naval missile.

      The SA-4 Ganef was a long-range mobile system first deployed in the mid-1960s; the missiles, carried in pairs on a tracked launcher, used drop-off solid-fuel boosters and a ramjet sustainer motor. Employing a combination of radar command guidance and active radar homing, and supported by an array of mobile radars for target acquisition, tracking, and guidance, they could engage targets over the horizon. (Because the SA-4 strongly resembled the earlier British Bloodhound, NATO assigned it the code name Ganef, meaning “Thief” in Hebrew.) Beginning in the late 1980s, the SA-4 was replaced by the SA-12 Gladiator, a more compact and capable system.

 The SA-5 Gammon was a high- and medium-altitude strategic missile system with a range of 185 miles; it was exported to Syria and Libya. The SA-6 Gainful was a mobile tactical system with a range of two to 35 miles and a ceiling of 50,000 feet. Three 19-foot missiles were carried in canisters atop a tracked transporter-erector-launcher, or TEL (see photograph—>), and the radar and fire-control systems were mounted on a similar vehicle, each of which supported four TELs. The missiles used semiactive radar homing and were powered by a combination of solid-rocket and ramjet propulsion. (The SA-N-3 Goblet was a similar naval system.) Gainful, the first truly mobile land-based SAM system, was first used in combat during the 1973 Arab-Israeli War and was highly effective at first against Israeli fighters. The Mach-3 missile proved virtually impossible to outmaneuver, forcing the fighters to descend below effective radar coverage, where antiaircraft guns such as the ZSU 23-4 mobile system were particularly lethal. (Similar factors prevailed in the 1982 Falklands (Falkland Islands War) conflict, where long-range British Sea Dart missiles achieved relatively few kills but forced Argentine aircraft down to wave-top level.) The SA-6 was replaced by the SA-11 Gadfly beginning in the 1980s.

      The SA-8 Gecko, first deployed in the mid-1970s, was a fully mobile system mounted on a novel six-wheeled amphibious vehicle. Each vehicle carried four canister-launched, semiactive radar homing missiles, with a range of about 7.5 miles, plus guidance and tracking equipment in a rotating turret. It had excellent performance but, in Syrian hands during the 1982 conflict in Lebanon, proved vulnerable to Israeli electronic countermeasures. The equivalent naval system was the widely deployed SA-N-4 Goblet.

      The SA-7 Grail shoulder-fired, infrared-homing missile was first deployed outside the Soviet Union in the final stages of the Vietnam War; it also saw extensive action in the Middle East. The SA-9 Gaskin carried four infrared-homing missiles on a turreted mount atop a four-wheeled vehicle. Its missiles were larger than the SA-7 and had more sophisticated seeker and guidance systems.

      The first generation of American SAMs included the Army Nike (Nike missile) Ajax, a two-stage, liquid-fueled missile that became operational in 1953, and the rocket-boosted, ramjet-powered Navy Talos. Both used radar tracking and target acquisition and radio command guidance. The later Nike Hercules, also command-guided, had a range of 85 miles. After 1956 the Talos was supplemented by the Terrier, a radar-beam rider, and the Tartar, a semiactive radar homing missile. These were replaced in the late 1960s by the Standard semiactive radar homing system. The solid-fueled, Mach-2 Standard missiles were deployed in medium-range (MR) and two-stage extended-range (ER) versions capable, respectively, of about 15 miles and 35 miles. Within 10 years a second generation of Standard missiles doubled the range of both versions. These newer missiles contained an inertial-guidance system that, by electronically communicating with the Aegis radar fire-control system, allowed corrections to be made in mid-course before the semiactive terminal homing took over.

      For 20 years, the most important land-based American SAM was the Hawk, a sophisticated system employing semiactive radar guidance. From the mid-1960s the Hawk provided the backbone of U.S. surface-based air defenses in Europe and South Korea and was exported to many allies. In Israeli use, Hawk missiles proved highly effective against low-flying aircraft. The longer-ranged Patriot missile system began entering service in 1985 as a partial replacement for the Hawk. Like the Hawk, the Patriot was semimobile; that is, the system components were not mounted permanently on vehicles and so had to be removed from their transport for firing. For target acquisition and identification, as well as for tracking and guidance, the Patriot system used a single phased-array radar, which controlled the direction of the beam by electronically varying the signals at several antennas rather than pivoting a single large antenna. The single-stage, solid-fueled Patriot missile was controlled by command guidance and employed track-via-missile homing, in which information from the radar in the missile itself was used by the launch site fire-control system.

      The shoulder-fired Redeye, an infrared-homing missile that was also deployed on truck-mounted launchers, was fielded in the 1960s to provide U.S. Army units close-in protection against air attack. After 1980 the Redeye was replaced by the Stinger, a lighter system whose missile accelerated faster and whose more advanced seeker head could detect the hot exhaust of approaching aircraft even four miles away and up to 5,000 feet in altitude.

      Western European mobile SAM systems include the German-designed Roland, an SA-8 equivalent fired from a variety of tracked and wheeled vehicles, and the French Crotale, an SA-6 equivalent that used a combination of radar command guidance and infrared terminal homing. Both systems were widely exported. Less directly comparable to Soviet systems was the British Rapier, a short-range, semimobile system intended primarily for airfield defense. The Rapier missile was fired from a small, rotating launcher that was transported by trailer. In the initial version, deployed in the early 1970s and used with some success in 1982 in the Falklands conflict, the target aircraft was tracked by a gunner using an optical sight. A television camera in the tracker measured differences between the missile's flight path and the path to the target, and microwave radio signals issued guidance corrections. The Rapier had a combat range of one-quarter to four miles and a ceiling of 10,000 feet. Later versions used radar tracking and guidance for all-weather engagements.

      A new generation of Soviet SAM systems entered service in the 1980s. These included the SA-10 Grumble, a Mach-6 mobile system with a 60-mile range deployed in both strategic and tactical versions; the SA-11 Gadfly, a Mach-3 semiactive radar homing system with a range of 17 miles; the SA-12 Gladiator, a track-mobile replacement of Ganef; the SA-13 Gopher, a replacement for Gaskin; and the SA-14, a shoulder-fired Grail replacement. Both Grumble and Gadfly had naval equivalents, the SA-N-6 and SA-N-7. The Gladiator might have been designed with an antimissile capability, making it an element of the antiballistic missile defense around Moscow.

John F. Guilmartin, Jr.

Strategic missiles
      Strategic missiles (missile) represent a logical step in the attempt to attack enemy forces at a distance. As such, they can be seen as extensions of either artillery (in the case of ballistic missiles) or manned aircraft (in the case of cruise missiles). Ballistic missiles are rocket-propelled weapons that travel by momentum in a high, arcing trajectory after they have been launched into flight by a brief burst of power. Cruise missiles, on the other hand, are powered continuously by air-breathing jet engines and are sustained along a low, level flight path by aerodynamic lift.

      Although experiments were undertaken before World War II on crude prototypes of the cruise and ballistic missiles, the modern weapons are generally considered to have their true origins in the V-1 (V-1 missile) and V-2 missiles (V-2 missile) launched by Germany in 1944–45. Both of those Vergeltungswaffen, or “Vengeance Weapons,” defined the problems of propulsion and guidance that have continued ever since to shape cruise and ballistic missile development.

      Given the extremely long ranges required of strategic weapons, even the most modern guidance systems cannot deliver a missile's warhead to the target with consistent, pinpoint accuracy. For this reason, strategic missiles have almost exclusively carried nuclear warheads, which need not strike a target directly in order to destroy it. By contrast, missiles of shorter range (often called tactical- or battlefield-range) have been fitted with both nuclear and conventional warheads. For example, the SS-1 Scud, a ballistic missile with ranges of up to 185 miles (300 kilometres), was fielded with nuclear warheads by Soviet troops in eastern Europe from the 1950s through the 1980s; but in the “war of the cities” during the Iran–Iraq (Iran-Iraq War) conflict of the 1980s, many SS-1s armed with conventional warheads were launched by both sides, killing thousands of civilians. Other “dual-capable” short-range ballistic missiles are the U.S. Lance (Lance missile), with a range of about 80 miles, and the Soviet SS-21 Scarab, with a range of 75 miles. (In this section, missile systems of the former Soviet Union are referred to by their NATO designations.)

      The exclusively nuclear capacity of strategic-range weapons confined serious development of cruise and ballistic missile technology to the world's nuclear powers—particularly the United States and the former Soviet Union. These two countries took different paths in exploiting missile technology. Soviet cruise missiles, for instance, were designed mostly for tactical antiship use rather than for threatening strategic land targets (as was the U.S. emphasis). Throughout the ballistic missile arms race, the United States tended to streamline its weapons, seeking greater accuracy and lower explosive power, or yield. Meanwhile, the Soviet Union, perhaps to make up for its difficulties in solving guidance problems, concentrated on larger missiles and higher yields. Most U.S. systems carried warheads of less than one megaton, with the largest being the nine-megaton Titan (Titan rocket) II, in service from 1963 through 1987. The Soviet warheads often exceeded five megatons, with the largest being a 20- to 25-megaton warhead deployed on the SS-7 Saddler from 1961 to 1980 and a 25-megaton warhead on the SS-9 Scarp, deployed from 1967 to 1982. (For the development of nuclear weapons, see nuclear weapon.)

      Most other countries pursuing missile technology have not developed strategic weapons to the extent of the United States and the former Soviet Union. Nonetheless, several other nations have produced them; their emphasis, however, has been on ballistic rather than cruise missiles because of the extremely sophisticated guidance systems required of cruise missiles. Also, as with any technology, there has occurred a transfer of ballistic missile technology to less-developed countries. Combined with the widespread capacity to produce chemical warheads, such weapons represent a potent addition to the arsenals of emerging powers of the Third World.

Ballistic missiles
Design principles
      Strategic ballistic missiles can be divided into two general categories according to their basing mode: those that are launched from land and those launched at sea (from submarines beneath the surface). They also can be divided according to their range into intermediate-range ballistic missiles (IRBMs) and intercontinental ballistic missiles (ICBMs). IRBMs have ranges of about 600 to 3,500 miles, while ICBMs have ranges exceeding 3,500 miles. Modern land-based strategic missiles are almost all of ICBM range, whereas all but the most modern submarine-launched ballistic missiles (SLBMs) have been of intermediate range.

      Prelaunch survivability (that is, the ability to survive an enemy attack) has been a long-standing problem with land-based ICBMs. (SLBMs achieve survivability by being based on relatively undetectable submarines.) At first, they were considered safe from attack because neither U.S. nor Soviet missiles were sufficiently accurate to strike the other's launch sites; hence, early systems were launched from above ground. However, as missile accuracies improved, above-ground missiles became vulnerable, and in the 1960s both countries began to base their ICBMs below ground in concrete tubes called silos, some of which were hardened against nuclear blast. Later, even greater improvements in accuracy brought ICBM basing strategy back to above-ground systems. This time, prelaunch survivability was to be achieved by mobile ICBMs that would confound an attacker with multiple moving targets.

      Most U.S. silos are designed for one-time “hot-launch” use, the rocket engines igniting within the silo and essentially destroying it as the missile departs. The Soviets pioneered the “cold-launch” method, in which the missile is expelled by gas and the rocket engine ignited after the missile clears the silo. This method, essentially the same system used with SLBMs, allows silos to be reused after minor repair.

      In order to increase their range and throw weight, ballistic missiles are usually multistaged. By shedding weight as the flight progresses (that is, by burning the fuel and then discarding the pumps, flight controls, and associated equipment of the previous stage), each successive stage has less mass to accelerate. This permits a missile to fly farther and carry a larger payload.

      The flight path of a ballistic missile has three successive phases. In the first, called the boost phase, the rocket engine (or engines, if the missile contains two or three stages) provides the precise amount of propulsion required to place the missile on a specific ballistic trajectory. Then the engine quits, and the final stage of the missile (called the payload) coasts in the midcourse phase, usually beyond the Earth's atmosphere. The payload contains the warhead (or warheads), the guidance system, and such penetration aids as decoys, electronic jammers, and chaff to help elude enemy defenses. The weight of this payload constitutes the missile's throw weight—that is, the total weight that the missile is capable of placing on a ballistic trajectory toward a target. By midcourse the warheads have detached from the remainder of the payload, and all elements are on a ballistic path. The terminal phase of flight occurs when gravity pulls the warheads (now referred to as the reentry vehicles, or RVs) back into the atmosphere and down to the target area.

      Most ballistic missiles use inertial guidance (inertial guidance system) to arrive at the vicinity of their targets. This technology, based on Newtonian physics, involves measuring disturbances to the missile in three axes. The device used to measure these disturbances is usually composed of three gyroscopically stabilized accelerometers mounted at right angles to one another. By calculating the acceleration imparted by external forces (including the rocket engine's thrust), and by comparing these forces to the launch position, the guidance system can determine the missile's position, velocity, and heading. Then the guidance computer, predicting the gravitational forces that will act on the reentry vehicle, can calculate the velocity and heading required to reach a predetermined point on the ground. Given these calculations, the guidance system can issue a command to the missile thrust system during boost phase to place the payload at a specific point in space, on a specific heading, and at a specific velocity—at which point thrust is shut off and a purely ballistic flight path begins.

      Ballistic missile guidance is complicated by two factors. First, during the latter stages of the powered boost phase, the atmosphere is so thin that aerodynamic flight controls such as fins cannot work and the only corrections that can be made to the flight path must come from the rocket engines themselves. But, because the engines only provide a force vector roughly parallel to the missile's fuselage, they cannot be used to provide major course corrections; making major corrections would create large gravitational forces perpendicular to the fuselage that could destroy the missile. Nevertheless, small corrections can be made by slightly gimballing the main engines so that they swivel, by placing deflective surfaces called vanes within the rocket exhaust, or, in some instances, by fitting small rocket engines known as thrust-vector motors or thrusters. This technique of introducing small corrections into a missile's flight path by slightly altering the force vector of its engines is known as thrust-vector control.

      A second complication occurs during reentry to the atmosphere, when the unpowered RV is subject to relatively unpredictable forces such as wind. Guidance systems have had to be designed to accommodate these difficulties.

      Errors in accuracy for ballistic missiles (and for cruise missiles as well) are generally expressed as launch-point errors, guidance/en-route errors, or aim-point errors. Both launch- and aim-point errors can be corrected by surveying the launch and target areas more accurately. Guidance/en-route errors, on the other hand, must be corrected by improving the missile's design—particularly its guidance. Guidance/en-route errors are usually measured by a missile's circular error of probability (CEP) and bias. CEP uses the mean point of impact of missile test firings, usually taken at maximum range, to calculate the radius of a circle that would take in 50 percent of the impact points. Bias measures the deviation of the mean impact point from the actual aim point. An accurate missile has both a low CEP and low bias.

The V-2 (V-2 missile)
      The precursor of modern ballistic missiles was the German V-2, a single-stage, fin-stabilized missile propelled by liquid oxygen and ethyl alcohol to a maximum range of about 200 miles. The V-2 was officially designated the A-4, being derived from the fourth of the Aggregat series of experiments conducted at Kummersdorf and Peenemunde under General Walter Dornberger (Dornberger, Walter Robert) and the civilian scientist Wernher von Braun (Braun, Wernher von).

      The most difficult technical problem facing the V-2 was achieving maximum range. An inclined launch ramp was normally used to give missiles maximum range, but this could not be used with the V-2 because the missile was quite heavy at lift-off (more than 12 tons) and would not be traveling fast enough to sustain anything approaching horizontal flight. Also, as the rocket used up its fuel its weight (and velocity) would change, and this had to be allowed for in the aiming. For these reasons the V-2 had to be launched straight up and then had to change to the flight angle that would give it maximum range. The Germans calculated this angle to be slightly less than 50°.

      The change in direction mandated some sort of pitch control during flight, and, because a change in pitch would induce yaw, control was needed on the yaw axis too. Added to these problems was the natural tendency of a cylinder to rotate. Thus, the V-2 (and every ballistic missile afterward) needed a guidance and control system to deal with in-flight rolling, pitching, and yawing. Using three-axis autopilots adapted from German aircraft, the V-2 was controlled by large vertical fins and smaller stabilizing surfaces to dampen roll and by vanes attached to the horizontal fins to modify pitch and yaw. Vanes were also installed in the exhaust nozzle for thrust vector control.

      A combination of in-flight weight changes and changes in atmospheric conditions presented additional problems. Even over the fairly limited course of a V-2 trajectory (with a range of approximately 200 miles and an altitude of roughly 50 miles), changes in missile velocity and air density produced drastic shifts in the distance between the centre of gravity and the centre of aerodynamic pressure. This meant the guidance system had to adjust its input to the control surfaces as the flight proceeded. As a result, V-2 accuracy never ceased to be a problem for the Germans.

      Still, the missile caused a great deal of damage. The first V-2 used in combat was fired against Paris on Sept. 6, 1944. Two days later the first of more than 1,000 missiles was fired against London. By the end of the war (World War II) 4,000 of these missiles had been launched from mobile bases against Allied targets. During February and March 1945, only weeks before the war in Europe ended, an average of 60 missiles was launched weekly. The V-2 killed an estimated five persons per launch (versus slightly more than two per launch for the V-1). Three major factors contributed to this difference. First, the V-2 warhead weighed more than 1,600 pounds (725 kilograms). Second, several V-2 attacks killed more than 100 people. Finally, there was no known defense against the V-2; it could not be intercepted and, traveling faster than sound, it arrived unexpectedly. The V-2 threat was eliminated only by bombing the launch sites and forcing the German army to retreat beyond missile range.

      The V-2 obviously ushered in a new age of military technology. After the war there was intense competition between the United States and the Soviet Union to obtain these new missiles, as well as to obtain the German scientists who had developed them. The United States succeeded in capturing both Dornberger and von Braun as well as more than 60 V-2s; it was not revealed precisely what (or whom) the Soviets captured. However, given the relative immaturity of ballistic missile technology at that time, neither country achieved usable ballistic missiles for some time. During the late 1940s and early 1950s most of the nuclear competition between the two countries dealt with strategic bombers. Events in 1957 reshaped this contest.

The first ICBMs
      In 1957 the Soviets launched a multistage ballistic missile (later given the NATO designation SS-6 Sapwood) as well as the first man-made satellite, Sputnik. This prompted the “missile gap” debate in the United States and resulted in higher priorities for the U.S. Thor (Thor rocket) and Jupiter IRBMs. Although originally scheduled for deployment in the early 1960s, these programs were accelerated, with Thor being deployed to England and Jupiter to Italy and Turkey in 1958. Thor and Jupiter were both single-stage, liquid-fueled missiles with inertial guidance systems and warheads of 1.5 megatons. Political difficulties in deploying these missiles on foreign soil prompted the United States to develop ICBMs, so that by late 1963 Thor and Jupiter had been terminated. (The missiles themselves were used extensively in the space program.)

      The Soviet SS-6 system was an apparent failure. Given its limited range (less than 3,500 miles), it had to be launched from northern latitudes in order to reach the United States. The severe weather conditions at these launch facilities (Novaya Zemlya and the Arctic mainland bases of Norilsk and Vorkuta) seriously degraded operational effectiveness; pumps for liquid propellants froze, metal fatigue was extreme, and lubrication of moving parts was nearly impossible. In 1960 a missile engine exploded during a test, killing Mitrofan Ivanovich Nedelin, chief of the Strategic Rocket Forces, and several hundred observers.

      Possibly as a result of these technical failures (and possibly in response to the deployment of Thor and Jupiter), the Soviets attempted to base the SS-4 Sandal, an IRBM with a one-megaton warhead and a range of 900–1,000 miles, closer to the United States and in a warmer climate. This precipitated the Cuban missile crisis of 1962, after which the SS-4 was withdrawn to Central Asia. (It was unclear whether the United States' deactivation of Thor and Jupiter was a condition of this withdrawal.)

      In the meantime, the United States was developing operational ICBMs to be based on U.S. territory. The first versions were the Atlas (Atlas rocket) and the Titan (Titan rocket) I. The Atlas-D (the first version deployed) had a liquid-fueled engine that generated 360,000 pounds of thrust. The missile was radio-inertial guided, launched above ground, and had a range of 7,500 miles. The follow-on Atlas-E/F increased thrust to 390,000 pounds, used all-inertial guidance, and moved from an aboveground to horizontal canister launch in the E and, finally, to silo-stored vertical launch in the F. The Atlas E carried a two-megaton, and the Atlas F a four-megaton, warhead. The Titan I was a two-stage, liquid-fueled, radio-inertial guided, silo-launched ICBM carrying a four-megaton warhead and capable of traveling 6,300 miles. Both systems became operational in 1959.

From liquid to solid fuel
      This first generation of missiles was typified by its liquid fuel, which required both a propellant and an oxidizer for ignition as well as a complex (and heavy) system of pumps. The early liquid fuels were quite dangerous, difficult to store, and time-consuming to load. For example, Atlas and Titan used so-called cryogenic (hypercold) fuels that had to be stored and handled at very low temperatures (−422° F [−252° C] for liquid hydrogen). These propellants had to be stored outside the rocket and pumped aboard just before launch, consuming more than an hour.

      As each superpower produced, or was thought to produce, more ICBMs, military commanders became concerned about the relatively slow reaction times of their own ICBMs. The first step toward “rapid reaction” was the rapid loading of liquid fuels. Using improved pumps, the reaction time of the Titan I was reduced from over one hour to less than 20 minutes. Then, with a second generation of storable liquids that could be kept loaded in the missile, reaction time was reduced to approximately one minute. Examples of second-generation storable-liquid missiles were the Soviet SS-7 Saddler and SS-8 Sasin (the latter deployed in 1963) and the U.S. Titan II. The Titan II was the largest ballistic missile ever developed by the United States. This two-stage ICBM was more than 100 feet long and 10 feet in diameter. Weighing more than 325,000 pounds at launch, it delivered its single warhead (with a throw weight of about 8,000 pounds) to a range of 9,000 miles and with a CEP of about one mile.

      In about 1964 China began developing a series of liquid-fueled IRBMs given the NATO designation CSS, for Chinese surface-to-surface missile. (The Chinese named the series Dong Feng, meaning “East Wind.”) The CSS-1 carried a 20-kiloton warhead to a range of 600 miles. The CSS-2, entering service in 1970, was fueled by storable liquids; it had a range of 1,500 miles and carried a one- to two-megaton warhead. With the two-stage CSS-3 (active from 1978) and the CSS-4 (active from 1980), the Chinese reached ICBM ranges of over 4,000 and 7,000 miles, respectively. The CSS-4 carried a warhead of four to five megatons.

      Because storable liquids did not alleviate the dangers inherent in liquid fuels, and because the flight times of missiles flying between the United States and the Soviet Union shrank to less than 35 minutes from launch to impact, still faster reactions were sought with even safer fuels. This led to a third generation of missiles, powered by solid propellants. Solid propellants were, eventually, easier to make, safer to store, lighter in weight (because they did not require on-board pumps), and more reliable than their liquid predecessors. Here the oxidizer and propellant were mixed into a canister and kept loaded aboard the missile, so that reaction times were reduced to seconds. However, solid fuels were not without their complications. First, while it was possible with liquid fuels to adjust in flight the amount of thrust provided by the engine, rocket engines using solid fuel could not be throttled. Also, some early solid fuels had uneven ignition, producing surges or abrupt velocity changes that could disrupt or severely confound guidance systems.

      The first solid-fueled U.S. system (Minuteman missile) was the Minuteman I. This ICBM, conceived originally as a rail-mobile system, was deployed in silos in 1962, became operational the following year, and was phased out by 1973. The first Soviet solid-fueled ICBM was the SS-13 Savage, which became operational in 1969. This missile could carry a 750-kiloton warhead more than 5,000 miles. Because the Soviet Union deployed several other liquid-fueled ICBMs between 1962 and 1969, Western specialists speculated that the Soviets experienced engineering difficulties in producing solid propellants.

      The French (France) deployed the first of their solid-fueled S-2 missiles in 1971. These two-stage IRBMs carried a 150-kiloton warhead and had a range of 1,800 miles. The S-3, deployed in 1980, could carry a one-megaton warhead to a range of 2,100 miles.

The first SLBMs
      Simultaneous with the early Soviet and U.S. efforts to produce land-based ICBMs, both countries were developing SLBMs. In 1955 the Soviets launched the first SLBM, the one- to two-megaton SS-N-4 Sark. This missile, deployed in 1958 aboard diesel-electric submarines and later aboard nuclear-powered vessels, had to be launched from the surface and had a range of only 350 miles. Partly in response to this deployment, the United States gave priority to its Polaris (Polaris missile) program, which became operational in 1960. Each Polaris A-1 carried a warhead of one megaton and had a range of 1,400 miles. The Polaris A-2, deployed in 1962, had a range of 1,700 miles and also carried a one-megaton warhead. The U.S. systems were solid-fueled, whereas the Soviets initially used storable liquids. The first Soviet solid-fueled SLBM was the SS-N-17 Snipe, deployed in 1978 with a range of 2,400 miles and a 500-kiloton warhead.

      Beginning in 1971, France deployed a series of solid-fueled SLBMs comprising the M-1, M-2 (1974), and M-20 (1977). The M-20, with a range of 1,800 miles, carried a one-megaton warhead. In the 1980s the Chinese fielded the two-stage, solid-fueled CSS-N-3 SLBM, which had a range of 1,700 miles and carried a two-megaton warhead.

Multiple warheads
      By the early 1970s, several technologies were maturing that would produce a new wave of ICBMs. First, thermonuclear warheads, much lighter than the earlier atomic devices, had been incorporated into ICBMs by 1970. Second, the ability to launch larger throw weights, achieved especially by the Soviets, allowed designers to contemplate adding multiple warheads to each ballistic missile. Finally, improved and much lighter electronics translated into more accurate guidance.

      The first steps toward incorporating these technologies came with multiple warheads, or multiple reentry vehicles (MRVs), and the Fractional Orbital Bombardment System (FOBS). The Soviets introduced both of these capabilities with the SS-9 Scarp, the first “heavy” missile, beginning in 1967. FOBS was based on a low-trajectory launch that would be fired in the opposite direction from the target and would achieve only partial earth orbit. With this method of delivery, it would be quite difficult to determine which target was being threatened. However, given the shallow reentry angles associated with a low trajectory and partial earth orbit, the accuracy of FOBS missiles was questionable. A missile carrying MRVs, on the other hand, would be launched toward the target in a high ballistic trajectory. Several warheads from the same missile would strike the same target, increasing the probability of killing that target, or individual warheads would strike separate targets within a very narrow ballistic “footprint.” (The footprint of a missile is that area which is feasible for targeting, given the characteristics of the reentry vehicle.) The SS-9, model 4, and the SS-11 Sego, model 3, both had three MRVs and ballistic footprints equal to the dimensions of a U.S. Minuteman complex. The only instance in which the United States incorporated MRVs was with the Polaris A-3, which, after deployment in 1964, carried three 200-kiloton warheads a distance of 2,800 miles. In 1967 the British adapted their own warheads to the A-3, and beginning in 1982 they upgraded the system to the A3TK, which contained penetration aids (chaff, decoys, and jammers) designed to foil ballistic missile defenses around Moscow.

      Soon after adopting MRVs the United States took the next technological step, introducing multiple independently targetable reentry vehicles (MIRVs (MIRV)). Unlike MRVs, independently targeted RVs could be released to strike widely separated targets, essentially expanding the footprint established by a missile's original ballistic trajectory. This demanded the capacity to maneuver before releasing the warheads, and maneuvering was provided by a structure in the front end of the missile called the “bus,” which contained the RVs. The bus was essentially a final, guided stage of the missile (usually the fourth), that now had to be considered part of the missile's payload. Since any bus capable of maneuvering would take up weight, MIRVed systems would have to carry warheads of lower yield. This in turn meant that the RVs would have to be released on their ballistic paths with great accuracy. As stated above, solid-fueled motors could be neither throttled nor shut down and restarted; for this reason, liquid-fueled buses were developed for making the necessary course corrections. The typical flight profile for a MIRVed ICBM then became approximately 300 seconds of solid-rocket boost and 200 seconds of bus maneuvering to place the warheads on independent ballistic trajectories.

      The first MIRVed system was the U.S. Minuteman III. Deployed in 1970, this three-stage, solid-fueled ICBM carried three MIRVs of an estimated 170 to 335 kilotons. The warheads had a range of 8,000 miles with CEPs of 725–925 feet. Beginning in 1970 the United States also MIRVed its SLBM force with the Poseidon (Poseidon missile) C-3, which could deliver up to 14 50-kiloton RVs to a range of 2,800 miles and with a CEP of about 1,450 feet. After 1979 this force was upgraded with the Trident C-4, or Trident I, which could deliver eight 100-kiloton MIRVs with the same accuracy as the Poseidon, but to a distance of 4,600 miles. Much longer range was made possible in the Trident by adding a third stage, by replacing aluminum with lighter graphite epoxies, and by adding an “aerospike” to the nose cone that, extending after launch, produced the streamlining effect of a pointed design while allowing the larger volume of a blunt design. Accuracy was maintained by updating the missile's inertial guidance during bus maneuvering with stellar navigation.

      By 1978 the Soviet Union had fielded its first MIRVed SLBM, the SS-N-18 Stingray. This liquid-fueled missile could deliver three or five 500-kiloton warheads to a distance of 4,000 miles, with a CEP of about 3,000 feet. On land in the mid-1970s, the Soviets deployed three MIRVed, liquid-fueled ICBM systems, all with ranges exceeding 6,000 miles and with CEPs of 1,000 to 1,500 feet: the SS-17 Spanker, with four 750-kiloton warheads; the SS-18 Satan, with up to 10 500-kiloton warheads; and the SS-19 Stiletto, with six 550-kiloton warheads. Each of these Soviet systems had several versions that traded multiple warheads for higher yield. For instance, the SS-18, model 3, carried a single 20-megaton warhead. This giant missile, which replaced the SS-9 in the latter's silos, had about the same dimensions as the Titan II, but its throw weight of more than 16,000 pounds was twice that of the U.S. system.

      Beginning in 1985, France upgraded its SLBM force with the M-4, a three-stage MIRVed missile capable of carrying six 150-kiloton warheads to ranges of 3,600 miles.

      A second generation of MIRVed U.S. systems was represented by the Peacekeeper. Known as the MX (Peacekeeper missile) during its 15-year development phase before entering service in 1986, this three-stage ICBM carried 10 300-kiloton warheads and had a range of 7,000 miles. Originally designed to be based on mobile railroad or wheeled launchers, the Peacekeeper was eventually housed in Minuteman silos. A second-generation MIRVed SLBM of the 1990s was the Trident D-5, or Trident II. Even though it was one-third again as long as its predecessor and had twice the throw weight, the D-5 could deliver 10 475-kiloton warheads to a range of 7,000 miles. Both the Trident D-5 and Peacekeeper represented a radical advance in accuracy, having CEPs of only 400 feet. The improved accuracy of the Peacekeeper was due to a refinement in the inertial guidance system, which housed the gyros and accelerometers in a floating-ball device, and to the use of an exterior celestial navigation system that updated the missile's position by reference to stars or satellites. The Trident D-5 also contained a star sensor and satellite navigator. This gave it several times the accuracy of the C-4 at more than twice the range.

      Within the generally less-advanced guidance technology of the Soviet Union, an equally radical advance came with the solid-fueled SS-24 Scalpel and SS-25 Sickle ICBMs, deployed in 1987 and 1985, respectively. The SS-24 could carry eight or 10 MIRVed warheads of 100 kilotons, and the SS-25 was fitted with a single 550-kiloton RV. Both missiles had a CEP of 650 feet. In addition to their accuracy, these ICBMs represented a new generation in basing mode. The SS-24 was launched from railroad cars, while the SS-25 was carried on wheeled launchers that shuttled between concealed launch sites. As mobile-based systems, they were long-range descendants of the SS-20 Saber, an IRBM carried on mobile launchers that entered service in 1977, partly along the border with China and partly facing western Europe. That two-stage, solid-fueled missile could deliver three 150-kiloton warheads a distance of 3,000 miles with a CEP of 1,300 feet. It was phased out after the signing of the Intermediate-Range Nuclear Forces (INF) Treaty in 1987.

Ballistic missile defense
      Although ballistic missiles followed a predictable flight path, defense against them was long thought to be technically impossible because their RVs were small and traveled at great speeds. Nevertheless, in the late 1960s the United States and Soviet Union pursued layered antiballistic missile (ABM) systems that combined a high-altitude interceptor missile (the U.S. Spartan and Soviet Galosh) with a terminal-phase interceptor (the U.S. Sprint and Soviet Gazelle). All systems were nuclear-armed. Such systems were subsequently limited by the Treaty on Anti-Ballistic Missile Systems (Anti-Ballistic Missile Treaty) of 1972, under a protocol in which each side was allowed one ABM location with 100 interceptor missiles each. The Soviet system, around Moscow, remained active and was upgraded in the 1980s, whereas the U.S. system was deactivated in 1976. Still, given the potential for renewed or surreptitious ballistic missile defenses, all countries incorporated penetration aids along with warheads in their missiles' payloads. MIRVs also were used to overcome missile defenses.

Maneuverable warheads
      Even after a missile's guidance has been updated with stellar or satellite references, disturbances in final descent could throw a warhead off course. Also, given the advances in ballistic missile defenses that were achieved even after the ABM treaty was signed, RVs remained vulnerable. Two technologies offered possible means of overcoming these difficulties. Maneuvering warheads, or MaRVs, were first integrated into the U.S. Pershing II IRBMs deployed in Europe from 1984 until they were dismantled under the terms of the INF Treaty. The warhead of the Pershing II contained a radar area guidance (Radag) system that compared the terrain toward which it descended with information stored in a self-contained computer. The Radag system then issued commands to control fins that adjusted the glide of the warhead. Such terminal-phase corrections gave the Pershing II, with a range of 1,100 miles, a CEP of 150 feet. The improved accuracy allowed the missile to carry a low-yield 15-kiloton warhead.

      MaRVs would present ABM systems with a shifting, rather than ballistic, path, making interception quite difficult. Another technology, precision-guided warheads, or PGRVs, would actively seek a target, then, using flight controls, actually “fly out” reentry errors. This could yield such accuracy that nuclear warheads could be replaced by conventional explosives.

Cruise missiles (cruise missile)
      The single most important difference between ballistic missiles and cruise missiles is that the latter operate within the atmosphere. This presents both advantages and disadvantages. One advantage of atmospheric flight is that traditional methods of flight control (e.g., airfoil wings for aerodynamic lift, rudder and elevator flaps for directional and vertical control) are readily available from the technologies of manned aircraft. Also, while strategic early-warning systems can immediately detect the launch of ballistic missiles, low-flying cruise missiles presenting small radar and infrared cross sections offer a means of slipping past these air-defense screens.

      The principal disadvantage of atmospheric flight centres around the fuel requirements of a missile that must be powered continuously for strategic distances. Some tactical-range antiship cruise missiles such as the U.S. Harpoon have been powered by turbojet engines, and even some non-cruise missiles such as the Soviet SA-6 Gainful surface-to-air missile employed ramjets to reach supersonic speed, but at ranges of 1,000 miles or more these engines would require enormous amounts of fuel. This in turn would necessitate a larger missile, which would approach a manned jet aircraft in size and would thereby lose the unique ability to evade enemy defenses. This problem of maintaining balance between range, size, and fuel consumption was not solved until reliable, fuel-efficient turbofan engines were made small enough to propel a missile of radar-evading size.

      As with ballistic missiles, guidance has been a long-standing problem in cruise missile development. Tactical cruise missiles generally use radio or inertial guidance to reach the general vicinity of their targets and then home onto the targets with various radar or infrared mechanisms. Radio guidance, however, is subject to line-of-sight range limitations, and inaccuracies tend to arise in inertial systems over the long flight times required of strategic cruise missiles. Radar and infrared homing devices, moreover, can be jammed or spoofed. Adequate long-range guidance for cruise missiles was not available until inertial systems were designed that could be updated periodically by self-contained electronic map-matching devices.

      Beginning in the 1950s, the Soviet Union pioneered the development of tactical air- and sea-launched cruise missiles, and in 1984 a strategic cruise missile given the NATO designation AS-15 Kent became operational aboard Tu-95 bombers. But Soviet programs were so cloaked in secrecy that the following account of the development of cruise missiles focuses by necessity on U.S. programs.

The V-1 (V-1 missile)
      The first practical cruise missile was the German V-1 of World War II, which was powered by a pulse jet that used a cycling flutter valve to regulate the air and fuel mixture. Because the pulse jet required airflow for ignition, it could not operate below 150 miles per hour. Therefore, a ground catapult boosted the V-1 to 200 miles per hour, at which time the pulse-jet engine was ignited. Once ignited, it could attain speeds of 400 miles per hour and ranges exceeding 150 miles. Course control was accomplished by a combined air-driven gyroscope and magnetic compass, and altitude was controlled by a simple barometric altimeter; as a consequence, the V-1 was subject to heading, or azimuth, errors resulting from gyro drift, and it had to be operated at fairly high altitudes (usually above 2,000 feet) to compensate for altitude errors caused by differences in atmospheric pressure along the route of flight.

      The missile was armed in flight by a small propeller that, after a specified number of turns, activated the warhead at a safe distance from the launch. As the V-1 approached its target, the control vanes were inactivated and a rear-mounted spoiler, or drag device, deployed, pitching the missile nose-down toward the target. This usually interrupted the fuel supply, causing the engine to quit, and the weapon detonated upon impact.

      Because of the rather crude method of calculating the impact point by the number of revolutions of a small propeller, the Germans could not use the V-1 as a precision weapon, nor could they determine the actual impact point in order to make course corrections for subsequent flights. In fact, the British publicized inaccurate information on impact points, causing the Germans to adjust their preflight calculations erroneously. As a result, V-1s often fell well short of their intended targets.

      Following the war there was considerable interest in cruise missiles. Between 1945 and 1948, the United States began approximately 50 independent cruise missile projects, but lack of funding gradually reduced that number to three by 1948. These three—Snark, Navaho, and Matador—provided the necessary technical groundwork for the first truly successful strategic cruise missiles, which entered service in the 1980s.

      The Snark was an air force program begun in 1945 to produce a subsonic (600-mile-per-hour) cruise missile capable of delivering a 2,000-pound atomic or conventional warhead to a range of 5,000 miles, with a CEP of less than 1.75 miles. Initially, the Snark used a turbojet engine and an inertial navigation system, with a complementary stellar navigation monitor to provide intercontinental range. By 1950, due to the yield requirements of atomic warheads, the design payload had changed to 5,000 pounds, accuracy requirements shrank the CEP to 1,500 feet, and range increased to more than 6,200 miles. These design changes forced the military to cancel the first Snark program in favour of a “Super Snark,” or Snark II.

      The Snark II incorporated a new jet engine that was later used in the B-52 bomber and KC-135A aerial tanker operated by the Strategic Air Command. Although this engine design was to prove quite reliable in manned aircraft, other problems—in particular, those associated with flight dynamics—continued to plague the missile. The Snark lacked a horizontal tail surface, it used elevons instead of ailerons and elevators for attitude and directional control, and it had an extremely small vertical tail surface. These inadequate control surfaces, and the relatively slow (or sometimes nonexistent) ignition of the jet engine, contributed significantly to the missile's difficulties in flight tests—to a point where the coastal waters off the test site at Cape Canaveral, Fla., were often referred to as “Snark-infested waters.” Flight control was not the least of the Snark's problems: unpredictable fuel consumption also resulted in embarrassing moments. One 1956 flight test appeared amazingly successful at the outset, but the engine failed to shut off and the missile was last seen “heading toward the Amazon.” (The vehicle was found in 1982 by a Brazilian farmer.)

      Considering the less than dramatic successes in the test program, the Snark, as well as other cruise missile programs, probably would have been destined for cancellation had it not been for two developments. First, antiaircraft defenses had improved to a point where bombers could no longer reach their targets with the usual high-altitude flight paths. Second, thermonuclear weapons were beginning to arrive in military inventories, and these lighter, higher-yield devices allowed designers to relax CEP constraints. As a result, an improved Snark was deployed in the late 1950s at two bases in Maine and Florida.

      The new missile, however, continued to exhibit the unreliabilities and inaccuracies typical of earlier models. On a series of flight tests, the Snark's CEP was estimated to average 20 miles, with the most accurate flight striking 4.2 miles left and 1,600 feet short. This “successful” flight was the only one to reach the target area at all and was one of only two to go beyond 4,400 miles. Accumulated test data showed that the Snark had a 33-percent chance of successful launch and a 10-percent chance of achieving the required distance. As a consequence, the two Snark units were deactivated in 1961.

      The second postwar U.S. cruise missile effort was the Navaho, an intercontinental supersonic design. Unlike earlier efforts, which were extrapolated from V-1 engineering, the Navaho was based on the V-2; the basic V-2 structure was fitted with new control surfaces, and the rocket engine was replaced by a turbojet/ramjet combination. Known by a variety of names, the Navaho emerged into a missile more than 70 feet long, with canard fins (i.e., control surfaces set forward of the wing), a V tail, and a large delta wing. (These flight control designs would eventually make their way onto other supersonic aircraft, such as the experimental XB-70 Valkyrie bomber, several fighter planes, and the supersonic transport.)

      With the exception of technologies associated with supersonic lift and control, few other aspects of the Navaho met designers' expectations. Most frustrating were difficulties with the ramjet engine, which was necessary for sustained supersonic flight. For a variety of reasons, including interrupted fuel flow, turbulence in the ramjet cavity, and clogging of the ramjet fire-ring, few of the engines ignited. This led engineers to label the project “Never Go, Navaho”—a name that stuck until the program was cancelled in 1958 after achieving only 1 1/2 hours airborne. No missile was ever deployed.

      Technologies explored in the Navaho program, besides those of flight dynamics, were used in other areas. Derivatives of the missile's titanium alloys, which were developed to accommodate surface temperatures at supersonic speed, came to be used on most high-performance aircraft. The rocket booster (which launched the missile until the ramjet ignited) eventually became the Redstone engine, which powered the Mercury manned spacecraft series, and the same basic design was used in the Thor and Atlas ballistic missiles. The guidance system, an inertial autonavigation design, was incorporated into a later cruise missile (Hound Dog) and was used by the nuclear submarine USS Nautilus for its under-the-ice passage of the North Pole in 1958.

Matador and other programs
      The third postwar U.S. cruise missile effort was the Matador, a ground-launched, subsonic missile designed to carry a 3,000-pound warhead to a range of more than 600 miles. In its early development, Matador's radio-controlled guidance, which was limited essentially to the line of sight between the ground controller and the missile, covered less than the missile's potential range. However, in 1954 an automatic terrain recognition and guidance (Atran) system was added (and the missile system was subsequently designated Mace). Atran, which used radar map-matching for both en-route and terminal guidance, represented a major breakthrough in accuracy, a problem long associated with cruise missiles. The low availability of radar maps, especially of areas in the Soviet Union (the logical target area), limited operational use, however. Nonetheless, operational deployments began in 1954 to Europe and in 1959 to Korea. The missile was phased out in 1962, its most serious problems being associated with guidance.

      While the U.S. Air Force (United States Air Force, The) was exploring the Snark, Navaho, and Matador programs, the navy (United States Navy, The) was pursuing related technologies. The Regulus, which was closely akin to the Matador (having the same engine and roughly the same configuration), became operational in 1955 as a subsonic missile launched from both submarines and surface vessels, carrying a 3.8-megaton warhead. Decommissioned in 1959, the Regulus did not represent much of an improvement over the V-1.

      A follow-on design, Regulus II, was pursued briefly, striving for supersonic speed. However, the navy's preference for the new large, angle-deck nuclear aircraft carriers and for ballistic missile submarines relegated sea-launched cruise missiles to relative obscurity. Another project, the Triton, was similarly bypassed due to design difficulties and lack of funding. The Triton was to have had a range of 12,000 miles and a payload of 1,500 pounds. Radar map-matching guidance was to have given it a CEP of 1,800 feet.

      In the early 1960s the Air Force produced and deployed the Hound Dog cruise missile on B-52 bombers. This supersonic missile was powered by a turbojet engine to a range of 400–450 miles. It used the guidance system of the earlier Navaho. The missile was so large, however, that only two could be carried on the outside of the aircraft. This external carriage allowed B-52 crew members to use the Hound Dog engines for extra thrust on takeoff, but the extra drag associated with the carriage, as well as the additional weight (20,000 pounds), meant a net loss of range for the aircraft. By 1976 the Hound Dog had given way to the short-range attack missile, or SRAM, essentially an internally carried, air-launched ballistic missile.

      By 1972, constraints placed on ballistic missiles by the SALT I treaty prompted U.S. nuclear strategists to think again about using cruise missiles. There was also concern over Soviet advances in antiship cruise missile technology, and in Vietnam remotely piloted vehicles had demonstrated considerable reliability in gathering intelligence information over previously inaccessible, highly defended areas. Improvements in electronics—in particular, microcircuits, solid-state memory, and computer processing—presented inexpensive, lightweight, and highly reliable methods of solving the persistent problems of guidance and control. Perhaps most important, terrain contour mapping, or Tercom, techniques, derived from the earlier Atran, offered excellent en route and terminal-area accuracy.

      Tercom used a radar or photographic image from which a digitalized contour map was produced. At selected points in the flight known as Tercom checkpoints, the guidance system would match a radar image of the missile's current position with the programmed digital image, making corrections to the missile's flight path in order to place it on the correct course. Between Tercom checkpoints, the missile would be guided by an advanced inertial system; this would eliminate the need for constant radar emissions, which would make electronic detection extremely difficult. As the flight progressed, the size of the radar map would be reduced, improving accuracy. In practice, Tercom brought the CEP of modern cruise missiles down to less than 150 feet (see Figure 1).

      Improvements in engine design also made cruise missiles more practical. In 1967 the Williams International Corporation produced a small turbofan engine (12 inches in diameter, 24 inches long) that weighed less than 70 pounds and produced more than 400 pounds of thrust. New fuel mixtures offered more than 30-percent increases in fuel energy, which translated directly into extended range.

      By the end of the Vietnam War, both the U.S. Navy and Air Force had cruise missile projects under way. At 19 feet three inches, the navy's sea-launched cruise missile (SLCM; eventually designated the Tomahawk) was 30 inches shorter than the air force's air-launched cruise missile (ALCM), but system components were quite similar and often from the same manufacturer (both missiles used the Williams engine and the McDonnell Douglas Corporation's Tercom). The Boeing Company produced the ALCM, while the General Dynamics Corporation produced the SLCM as well as the ground-launched cruise missile, or GLCM. The SLCM and GLCM were essentially the same configuration, differing only in their basing mode. The GLCM was designed to be launched from wheeled transporter-erector-launchers, while the SLCM was expelled from submarine tubes to the ocean surface in steel canisters or launched directly from armoured box launchers aboard surface ships. Both the SLCM and GLCM were propelled from their launchers or canisters by a solid-rocket booster, which dropped off after the wings and tail fins flipped out and the jet engine ignited. The ALCM, being dropped from a bomb-bay dispenser or wing pylon of a flying B-52 or B-1 bomber, did not require rocket boosting.

      As finally deployed, the U.S. cruise missiles were intermediate-range weapons that flew at an altitude of 100 feet to a range of 1,500 miles. The SLCM was produced in three versions: a tactical-range (275-mile) antiship missile, with a combination of inertial guidance and active radar homing and with a high-explosive warhead; and two intermediate-range land-attack versions, with combined inertial and Tercom guidance and with either a high-explosive or a 200-kiloton nuclear warhead. The ALCM carried the same nuclear warhead as the SLCM, while the GLCM carried a low-yield warhead of 10 to 50 kilotons.

      The ALCM entered service in 1982 and the SLCM in 1984. The GLCM was first deployed to Europe in 1983, but all GLCMs were dismantled after the signing of the INF Treaty.

      Although their small size and low flight paths made the ALCM and SLCM difficult to detect by radar (the ALCM presented a radar cross section only one one-thousandth that of the B-52 bomber), their subsonic speed of about 500 miles per hour made them vulnerable to air defenses once they were detected. For this reason, the U.S. Air Force began production of an advanced cruise missile, which would incorporate stealth technologies such as radar-absorbent materials and smooth, nonreflective surface shapes. The advanced cruise missile would have a range of over 1,800 miles.

Stephen Oliver Fought

Additional Reading
On missile systems, see Kenneth W. Gatland, Development of the Guided Missile, 2nd ed. (1954), a somewhat technical examination of early efforts. Other historical works include Homer E. Newell, Guide to Rockets, Missiles, and Satellites, 2nd rev. ed. (1961); Eric Burgess, Long-Range Ballistic Missiles (1961); E. Michael Del Papa, From SNARK to SRAM: A Pictorial History of Strategic Air Command Missiles (1976); Norman Polmar, Strategic Weapons: An Introduction, rev. ed. (1982); and Kenneth P. Werrell, The Evolution of the Cruise Missile (1985). Characteristics of strategic weapons are covered in Michael J.H. Taylor, Missiles of the World, 3rd ed. (1980); and Philip Birtles and Paul Beaver, Missile Systems (1985). Some insight into future developments is suggested in Max Walmer, An Illustrated Guide to Strategic Weapons (1988). The latest developments in the field are covered in Jane's Weapon Systems (annual) and The International Countermeasures Handbook (annual).Stephen Oliver Fought John F. Guilmartin, Jr.

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