Rockets, missiles, and nuclear weapons

Dates Since c. 1200

Nature and Use of Rockets and Missiles

Although the terms “rocket” and “missile” are sometimes used interchangeably, when speaking of weapons, the term “rocket” generally refers either to the means of propulsion or to a relatively small rocket projectile, and the term “missile” usually refers to a more complex weapon. A ballistic missile follows a ballistic trajectory—the path a thrown rock would take—for most of its flight and is guided only during or shortly after launch.

At its most basic, a rocket motor is simply a chamber with a nozzle at the rear. Fuel is burned in the chamber to produce hot, pressurized gases that then are exhausted through the nozzle. In accordance with Isaac Newton’s third law of motion, which states that for every action there is an equal and opposite reaction, the rocket is pushed forward by expelling these exhaust gases backward out of the nozzle. The rocket is not pushed forward by the exhaust gases pushing against the air behind the rocket, as is sometimes supposed. In fact, because a rocket carries its fuel along with an oxidizer to burn it, a rocket does not need air and can operate in the vacuum of space.

Although it is not known exactly when the first rocket was invented, its origins likely lie with the fire-arrow, a tube filled with burning powder attached to an arrow. Gases escaping from the tube helped propel the arrow, and sparks from the burning powder conveniently started fires. Thirteenth-century Mongol leader Genghis Khan (r. 1206–27) used fire-arrows in battle, and in 1429, French troops under Joan of Arc (c. 1412–31) used rockets in the defense of Orléans. Improvements led eventually to the war rockets of Tipu, Sultan of Mysore in the south of India (r. 1782–99), who used them in 1792 to terrorize British soldiers.

Colonel William Congreve (1772–1828) at London’s Woolrich Arsenal was assigned to study Tipu’s rockets and to develop a rocket for the British artillery that could be made in large numbers. The product of his research, the Congreve rocket, had a range of 2.7 kilometers and consisted of an iron case filled with black powder. The case was attached to a long stabilizing stick, and air drag on the stick kept the rocket pointed forward. A chamber on the front of the rocket held either an incendiary or an explosive that was ignited by a fuse.

Congreve considered rockets to be ideal weapons for ships, because there is no recoil, as there is with cannons. In 1806, during the Napoleonic Wars, the British navy fired two thousand Congreve rockets at the French in Boulogne, setting several buildings ablaze. In 1807 thirty thousand rockets were fired into Copenhagen and set much of that city on fire. Inspired by the barrage of Congreve rockets fired by the British against Fort McHenry during the War of 1812, Francis Scott Key wrote his poem “The Star-Spangled Banner,” which became the US national anthem.

Later, William Hale of Britain dispensed with the clumsy guide stick and spin-stabilized the rocket by placing three slanted metal vanes in the rocket’s exhaust. The Hale rocket was used by the United States during the Mexican War. However, as artillery evolved in accuracy, rockets were employed less frequently, except for special uses, such as carrying lightweight lines from rescuers to stranded ships.

Rockets and missiles can be divided roughly into three groups, depending upon their ranges. Battlefield weapons are used in a local area, with the combatants often within sight of each other. Theater missiles have ranges of 160 to 3,200 kilometers, whereas intercontinental missiles have longer ranges. Both theater weapons (except low-flying cruise missiles) and intercontinental missiles rise through the atmosphere and coast through space before reentering the atmosphere to strike their targets.

Development of Rockets and Missiles

After military interest in rocketry declined, progress depended upon the efforts of a few indefatigable individuals, such as American physics professor Robert H. Goddard (1882–1945), who took a practical engineering approach. Goddard began by experimenting with solid-fuel rockets and developed a portable rocket, the forerunner of the bazooka, for the military. He became the world pioneer in the development of liquid-fuel rockets, but his work was eventually surpassed by that of Wernher von Braun (1912–77) and his associates, who were working for the German military.

World War II

With Germany leading the way, World War II saw the reemergence of the rocket as a useful weapon. The post-World War I Treaty of Versailles (1919) had limited the number of artillery pieces Germany could possess but had not mentioned rockets. Germany exploited this loophole and began rocket research and development in earnest during the 1930s. Battlefield rockets were used by several nations during World War II, but only Germany used theater weapons: the V-1 and V-2. Germany also had begun design work on an intercontinental missile before the end of the war.

World War II battlefield rockets included barrage rockets, antitank rockets, and rockets fired from aircraft. Although barrage rockets were not extremely accurate, they could be fired by the hundreds to saturate an area. The German Nebelwerfer, or “fog thrower,” began as a weapon used to lay down a smoke screen but was adapted to fire barrage rockets. The Nebelwerfer, a towed 6-tube launcher, was nicknamed Moaning Minnie by the Allies because of the eerie sound made by its incoming rockets. Its range was up to 6,000 meters. US barrage rockets could be fired from the Calliope, a 60-tube launcher mounted on the turret of a Sherman tank. When fired in massive numbers, the rockets were ripple-fired, or fired in rapid succession, to minimize one rocket destroying another in the air. The Soviets launched Katyusha rockets from the Stalin Organ, a launcher with 16 to 48 tubes mounted on a gun carriage. The British navy equipped some landing craft with Mattress Projectors, which could fire about 1,000 rockets in 45 seconds. Two such craft could deliver 27,000 kilograms (60,000 pounds) of explosives in less than a minute. The rockets had a range of 3 to 6 kilometers and were used for heavy coastal bombardments prior to landings.

US troops took the Germans by surprise in North Africa with the introduction of the bazooka, a rocket-powered grenade. The rocket, launched from a shoulder-held tube, could disable a moving tank up to 200 meters away and knock out stationary targets up to 700 meters away. The Germans soon answered with antitank rockets of their own: the Panzerfaust and the Panzerschreck.

Germany worked on several air-launchedmissiles, but the most successful were the radio-controlled glide bombs Henschel HS 293 and the Fritz-X, also known as the Ruhrstahl SD-1400. When launched, a flare mounted on the missile’s tail ignited, and the bombardier watched the flare while using radio-controlled flaps and spoilers to guide the missile to its target. Glide bombs were quite successful when they were first deployed in the summer of 1943. The rocket-powered HS 293 was used against convoy escort ships. The armor-piercing Fritz-X sank or disabled a number of warships, including battleships and cruisers. These missiles would have been even more successful, but they were subject to radio jamming. The controlling aircraft also were vulnerable, and, after the Allies gained air superiority, German bombers could no longer get close enough to their targets to use these missiles.

Russianaircraft successfully used unguided salvos of RS-82, and later, RS-132, rockets against ground troops and armor. British aircraft used their “60-pounder” to decimate German tanks. The 60-pounder was named for the weight of its high-explosive warhead. General-purpose rockets, such as the US 4.5-inch (114-millimeter) HE M8 rocket, were used against vehicle convoys, tanks, trains, fuel and ammunition depots, airfields, and barges. In mid-1944, the M8 was upgraded to the 5-inch (127-millimeter) High Velocity Air Rocket (HVAR), also known as the Holy Moses because of its impressive destructive effect.

The V-1

The Allies had no counterpart to the German theater missiles, the V-1 and V-2. The V-1 was a cruise missile with a maximum range of about 260 kilometers and a top speed of 645 kilometers per hour. Launched from the Pas de Calais area of France, it could reach London in twenty-two minutes. It carried 850 kilograms of high explosives and could have carried nerve gas, but German leader Adolf Hitler was under the mistaken impression that the Allies also had nerve gas and would have used it. Hitler launched the V-1’s in retaliation for the Allied bombing of Germany, hence the name Vergeltungswaffen Einz, meaning Retaliation Weapon One. This translation quickly evolved to the pithier Vengeance Weapon One, or V-1.

The V-1’s motor was a surprisingly simple pulse jet: a long stovepipe with shutter strips across the air intake at the front end. Air mixed with fuel was exploded by a spark plug. The explosion closed the shutter strips, forcing the exhaust gases out the back end. Incoming air opened the strips, and the process repeated forty-two times a minute, making a characteristic low rumble or buzzing sound that inspired the name “buzz-bomb.” The motor only worked at high speeds, so the V-1 was flung into the air at 400 kilometers per hour (250 miles per hour) from a 48-meter-long ramp equipped with a steam catapult.

Beginning in June 1944, more than 8,000 V-1’s were fired at London. Many failed, many were shot down, but about 2,400 arrived. When a timing mechanism indicated that the missile was over its target, the flight control surfaces put the missile into a dive that normally extinguished the engine. Londoners learned to dread hearing the buzzing stop. Over six thousand people were killed and another forty thousand were wounded by V-1’s. The bombs destroyed 130,000 British homes and damaged an additional 750,000. The Germans sent 9,000 V-1’s against various cities in Europe, including 5,000 against the Belgian port city, Antwerp.

The V-2

V-2’s were about twenty times as expensive to build as V-1’s, but both weapons carried enough explosives to destroy a large building. V-1’s were developed by the German air force, whereas V-2’s were developed by Wernher von Braun and his associates for the German army. Both weapons were manufactured by forced laborers working under deplorable conditions. The V-2 burned liquid oxygen and ethyl alcohol mixed with water, and it weighed about 12,300 kilograms at launch. Although powered flight lasted only seventy seconds, by then the rocket’s speed was nearly five times the speed of sound. It had a 320-kilometer range and could reach England in about five minutes. Because it traveled so quickly, there was no defense against it. Furthermore, the V-2’s mobile launch facilities were difficult to find and destroy.

More than 1,100 V-2’s fell in southern England beginning in September 1944, killing about 2,700 people and injuring over twice that number. About half of these V-2’s hit London. Between December 1944, and the end of March 1945, when all V-2 operations ceased, about 2,100 V-2’s were fired at Antwerp. Seventeen percent of these exploded on the launch pad, 18 percent failed in the air, but 65 percent reached Antwerp, often striking within several hundred meters of their targets. A total of 7,000 people were killed by V-2’s. The V-1 killed about two people per launch, and the V-2 killed about five people per launch. Had either weapon been used in sufficient numbers two or three years earlier, the course of the war might have been different. Although neither weapon ultimately had much effect on the war, the development of the V-2 led directly to the missiles and spaceships that followed it.

Development of Modern Battlefield Missiles

Great improvements in missile accuracy required the development of better sensors and of sophisticated electronics based on integrated circuits. Integrated circuits became available in the early 1960s and grew progressively more complex and more reliable.

Antitank Missiles

On the day after the Soviet Sagger antitank missile was introduced in the Vietnam War in 1972, the Americans introduced its counterpart, the TOW missile. TOW is an acronym for tube-launched, optically tracked, and wire-command-link-guided. During the brief 1973 Israeli-Arab October War, TOW and Sagger missiles together destroyed more than 1,500 Israeli, Jordanian, Iraqi, and Syrian tanks.

After a TOW is launched, the gunner must keep the crosshairs of the launch tube sight centered on the target until the missile impacts. As the missile flies at half the speed of sound, a thin wire unreels behind it. A small beacon on the missile’s tail sends an infrared signal to a sensor on the launch tube, and a computer in the launch tube sends flight corrections back to the missile through the connecting wire and guides the missile to the target. The TOW can be fired from the ground using a tripod-mounted tube or from launchers mounted on vehicles, including the high-mobility multipurpose wheeled vehicle (HMMWV) and the Cobra helicopter. There have been five major upgrades to the TOW, which is used by forty-three Allied countries.

Antitank missiles such as the TOW and the Sagger often use a shaped charge that explodes on impact and focuses the explosive energy into a small jet that can penetrate the tank armor. In defense, sandwich armor consisting of an outer steel plate and a thick inner steel plate was developed. Three types of sandwich material have been used: honeycomb ceramic that flows under impact and disrupts the projectile’s explosive jet; depleted uranium that retards the projectile’s momentum with its massive inertia; and a layer of explosive that detonates and pushes back against the impacting projectile. The latter is called Explosive Reactive Armor (ERA).

The nose of the TOW 2A has an extended probe and a small disrupter charge. The probe and the disrupter charge detonate the reactive armor, and after its protective effect is expended, the main shaped charge explodes and penetrates the main armor. The TOW 2A can penetrate any armor currently in use. The TOW 2B flies over the top of the targeted tank, which is less protected than the sides. When laser and magnetic sensors alert the missile that it is above the tank, two tantalum penetrator projectiles are explosively formed. One is fired directly downward, and the other is fired slightly off to the side to increase the hit probability. The projectile material is designed to start fires within the target. The TOW 2B is expected to be effective against any tank developed in the near future. The TOW FF, a wireless TOW fire-and-forget missile allowing gunners to dive for cover or engage other targets, is under development.

Air Defense Missiles

Just as TOW missiles enable soldiers to stop tanks, surface-to-air missiles (SAMs)—man-portable air defense systems (MANPADS) in their smallest versions—enable troops to counter high-speed, low-level, ground-attack aircraft, or bring down high-flying aircraft. After World War II, German rocket technology was adapted to Cold War needs, though it was not until the late 1950s that it proved to be effective. The Soviet Union was in the forefront of SAM development, adapting German models to the new battlefield climate. One of the most notable achievements of this emerging technology came on May 1, 1960, when the Soviet Union downed a U-2 spy plane, piloted by Gary Powers, with an SA-2 surface-to-air missile. After that time, several generations of SAMs and MANPADS were developed, leading to greater precision and portability. Older technologies are widely available and relatively inexpensive, while more sophisticated versions are readily available to organizations or individuals with sufficient funding. As a result, MANPADS became a characteristic weapon of the late Cold War and in the practice of terrorism.

One of the most widely used systems, the FIM-92 Stinger, was developed by the United States and provided to Islamic guerrilla fighters, the Mujahideen, in Afghanistan for use in their defense against Soviet invasion during the 1980s. It is estimated that more than 270 Soviet aircraft were shot down with Stingers. When the gunner sights an aircraft, he can send an electronic signal to identify whether it is friend or foe. The Stinger is another fire-and-forget weapon: Once it has been launched, the gunner can dive for cover or engage another target. The Stinger uses both infrared and ultraviolet sensors to home in on the target and can approach it from any aspect. Its speed is supersonic, and its maximum range is 8 kilometers. As global terrorism expanded following the attacks of September 11, 2001, military planners recognized the danger of MANPAD attacks, particularly against civilian aircraft, but no cost-efficient countermeasure could be found.

Missiles in the Gulf War

Several modern missiles were put to the test during the 1991 Gulf War. The start of the air war came during the dark early morning hours of January 17, 1991, when eight Apache helicopters launched laser-guided Hellfiremissiles and Hydra-70 rockets against two Iraqi early-warning ground control radar sites. The Iraqi air defense system was so extensive that only Moscow was judged to be better defended than Baghdad. Because of this, only unmanned cruise missiles and the nearly invisible Stealth aircraft penetrated deeply into Iraq at first. The first goal was to create gaps in the Iraqi air defense and open the way for more conventional aircraft. F-4G Wild Weasel aircraft broadcast strong radar jamming signals and also recorded Iraqi radar signals, playing them back with various delays to clutter Iraqi radar displays with floods of false targets.

Development of Modern Cruise Missiles

Cruise missiles are theater weapons. Early cruise missiles, such as the Snark, the Matador, and the Hound Dog, deployed in the 1950s and 1960s, suffered from various problems, especially unreliability and inaccuracy. However, as bombers found it ever more difficult to penetrate improved air-defense systems, stand-off, unmanned weapons became increasingly attractive. Eventually improvements in engine technology and guidance systems led to the modern cruise missiles originally deployed in the 1980’s and used during and after the Gulf War.

The Tomahawk cruise missile is launched from surface ships and submarines with a solid propellant rocket that burns for twelve seconds, after which a small turbofan motor takes over and propels the missile at 880 kilometers per hour (550 miles per hour). The Tomahawk is not easy to shoot down, because it is difficult to track. Detection by radar is difficult, because the missile is small and cruises at only 15 to 30 meters above the ground. Detection by infrared sensors is also difficult, because the turbofan motor puts out very little heat.

All versions of the Tomahawk use an inertial navigation system (INS) while over water. The INS has four crucial elements: gyroscopes, inertial masses, a computer, and an accurate clock. By measuring the magnitude and duration of the forces on the inertial masses and by using the gyroscopes to establish direction, the computer can calculate the missile’s acceleration, velocity, and position. If the computer finds that the missile is not where it should be, commands can be sent to the flight control surfaces to correct its course.

The Tomahawk BGM-109B is a ship-to-ship weapon with a range of 470 kilometers. When it reaches its target area, it circles until it locks onto the enemy ship’s radar or locates the ship with its own radar. It carries a 450-kilogram semi-armor-piercing warhead and can either strike the target broadside or pop up and dive down on the target. A ground-launched Tomahawk, the BGM-109A, was briefly deployed in Europe but was removed under a provision of the 1988 Intermediate-range and shorter-range Nuclear Forces (INF) treaty. The Tomahawk has a range of 2,500 kilometers and carries a 200-kiloton nuclear warhead. In addition to INS, the Tomahawk has a Terrain Contour Matching System (TERCOM), which, at selected checkpoints, scans the terrain with radar, comparing topographical features against stored data and correcting its flight path as necessary. To avoid detection, the radar remains off most of the time. The accuracy of the Tomahawk’s TERCOM system was such that 50 percent of the missiles would hit within 45 meters of their targets, close enough for the 200-kiloton nuclear warheads to destroy the targets.

The Tomahawk BGM-109C and Tomahawk BGM-109D have ranges of 1,600 kilometers. Both weapons use, in addition to INS and TERCOM, the Global Positioning System (GPS). When they near their targets, they also employ a Digital Scene Matching Area Correlator (DSMAC) that compares images from an electronic camera in the missile nose against stored data. The DSMAC system makes these weapons exceptionally accurate, reducing their error probability to 10 meters. The missile can hit the target horizontally, pop up and dive down on the target, or fly over and burst above the target. The 109D is similar to the 109C but dispenses 166 BLU-97/B Combined Effect Munitions (CEM). Each CEM is about the size of a soft-drink can, weighs about 1.5 kilograms, and consists of three types of submunitions: fragmentation, incendiary, and shaped-charges that can penetrate 13 to 18 centimeters of armor. The 109D can dispense the CEMs in batches on several targets.

The air-launched cruise missile (ALCM) AGM-86 uses INS, TERCOM, and GPS guidance systems. It originally carried a 200-kiloton nuclear warhead but has been converted to carry a massive 900-kilogram (2,000-pound) blast-fragmentation warhead that sprays a cloud of ball bearings. The ALCM is designed to destroy dispersed, soft targets such as surface-to-air missile batteries. B-52G and B-52H bombers can carry twelve missiles in external racks, and some B-52H bombers can carry eight more missiles internally.

On January 17, 1991, at the start of the Gulf War, 297 Tomahawks were prepared to be launched from ships, but nine failed prelaunch tests. Of the 288 actual launches, 6 failed to cruise and 242 (81 percent of those launched) hit their targets. At about the same time, high-flying bombers launched thirty-five ALCMs at targets in Iraq. Televison reporters watched in amazement as missiles streaked past their hotel and made right turns into the next street on their way to their targets.

In January 1993, forty-five Tomahawks were launched against Iraqi nuclear development facilities and similar targets. In September 1995, thirteen Tomahawks hit surface-to-air missile sites in Bosnia. As a response to Iraqi harassment of Western aircraft patrolling the no-fly zone, 13 ALCMs were fired from B-52Hs and thirty-one Tomahawks were fired from ships in the Persian Gulf in September, 1996. In response to the terrorist bombings of US embassies in Kenya and Tanzania, thirteen Tomahawks destroyed a suspected chemical weapons factory in the Sudan, and sixty-six Tomahawks hit guerrilla training camps in Afghanistan in August 1998. Striking against weapons of mass destruction and Iraqi air-defense sites in December 1998, the United States and Britain attacked about one hundred targets in central and southern Iraq. They used fighters, bombers, ninety ALCMs, and 330 Tomahawks. In March 1999, NATO (North Atlantic Treaty Organization) forces struck targets in Yugoslavia and Kosovo with fighters, bombers, and one hundred cruise missiles.

Cruise missiles seem to have become the weapon of choice in many situations. Although laser-guided bombs can be up to ten times more accurate and are significantly less expensive to build, they put pilots at risk. Even though a few cruise missiles do go astray and cause unintended damage, they have proven accurate enough and reliable enough to be used against targets surrounded by civilians. Future upgrades will cut the production costs of cruise missiles in half by discontinuing the capability to launch them from torpedo tubes, including a small television camera for tracking the target, replacing mechanical gyroscopes with laser-ring gyroscopes, and giving them the ability to be redirected to new targets while in flight.

Development of Intercontinental Ballistic Missiles

After World War II, the United States and the Soviet Union experimented with captured German V-2 rockets and worked to develop intercontinental ballistic missiles (ICBMs). In 1957 the Soviets launched an SS-6 Sapwood multistage ballistic missile and also put the first two artificial satellites, Sputnik 1 and Sputnik 2, into orbit. (A multistage rocket has the advantage that the excess weight of spent stages can be discarded.) The United States suddenly perceived a “missile gap” and reinvigorated its own missile program. The first US satellite, Explorer 1, was lifted into orbit by a Juno 1 rocket atop a Jupiter C on January 31, 1958. The Jupiter ICBM was declared operational in 1958 and deployed in Italy and Turkey, while the Thor missile became operational in 1959 and was deployed in the United Kingdom. Both missiles were liquid fueled, with ranges of 3,200 kilometers. They had inertial guidance systems and carried 1.5-megaton nuclear warheads.

The Soviet SS-6 had a range of about 5,600 kilometers (3,500 miles) and had to be launched from northern latitudes in order to reach the United States, but the bitter northern cold often rendered the missile inoperable. Perhaps in response to the failure of the SS-6 and to the deployment of the Thor and Jupiter, the Soviet Union attempted to base SS-4 Sandal missiles in Cuba, thereby precipitating the Cuban Missile Crisis of 1962. The SS-4 carried a 1-megaton warhead and had a range of about 1,600 kilometers. After coming to the brink of nuclear war, the Soviets withdrew these missiles. Not long afterward, the Jupiter and Thor missiles were retired from service in 1964 and 1965, respectively.

Missiles deployed in the homeland are not subject to the consent of other nations. The Atlas and Titan I missiles were both deployed in the United States in 1959. These were liquid fueled, carried 2- to 4-megaton warheads, and had inertial or radio-inertial guidance systems. The Atlas had a range of about 16,000 kilometers and used liquid hydrogen. The Titan I was a two-stage missile with a range of about 10,000 kilometers. It used liquid oxygen, a cryogenic (supercold) liquid that had to be pumped onboard during a lengthy procedure during launch preparation. The Titan II used storable liquid fuels that could remain in the missile so it could be launched more quickly. It weighed 148 metric tons (325,000 pounds) at liftoff and was the largest missile ever deployed by the United States. More than 30 meters long and 3 meters in diameter, it had a range of 14,500 kilometers and a throw weight of 3.6 metric tons. It delivered a 9-megaton nuclear warhead, so it did not matter that its CEP was 1.6 kilometers.

Solid-Fuel Rockets

Because a Soviet ICBM could reach the United States in thirty-five minutes, the United States needed antiballistic missiles (ABMs) that could be fired in minutes, so solid-fuel rockets were developed. Solid fuels are more stable than liquid fuels and do not require heavy pipes and pumps. Although they were always ready to fire, they made flight control more difficult, because solid-fueled rockets could not be throttled back nor use gimbal-mounted motors to steer. The Minuteman I became operational in 1962 and was the first US solid-fueled missile. It was held ready in a underground silo and had a range of 10,000 kilometers.

In the mid-1960s, the Soviets, the British, and the United States equipped some of their missiles with multiple reentry vehicles (MRVs), warheads that separated before the missile returned into the atmosphere. Several warheads from the same missile striking the target area made it more likely that the target would be destroyed. In 1982 the British used MRVs to incorporate penetration aids such as decoys, radar-reflecting chaff, and electronic jammers in missiles designated to attack Moscow, which was protected by an antiballistic missile shield. The United States took the next step and developed multiple independently targetable reentry vehicles (MIRVs) to penetrate the nationwide antiballistic missile system that it feared the Soviets would build. The missile payload was now a bus that could maneuver in space and send its warheads to different targets. It had to be liquid fueled so that it could repeatedly start and stop its rocket motors. The United States deployed its first MIRVed missile, the Minuteman III, in 1970. Its first three stages were solid fueled, with a range of 13,000 kilometers and a CEP of 365 meters. That was close enough because it carried three 200- to 350-kiloton nuclear warheads.

The United States feared that not enough Minuteman missiles in its silos would survive a Soviet preemptive strike and decided to build a mobile missile, the MX Peacekeeper. It carried up to ten 300-kiloton nuclear warheads, with a range of 11,000 kilometers and a CEP of 90 meters. Because no satisfactory mobile basing plan was found, the MX was housed in Minuteman silos. Its radically improved accuracy was due to a new inertial guidance system in which the gyros and accelerometers were housed in a floating ball. It also updated its position by sighting stars or certain satellites. Many consider the MX to be a first-strike weapon, because it is accurate enough to destroy missiles in their silos.

The Strategic Arms Reduction Treaty II (START II, 1993–2000) required the United States to remove MIRV capability from its ICBMs. Although the treaty was never formally put into force, both the United States and Russia generally followed its provisions. MX missiles were retired and Minuteman III missiles were refitted with single 300-kiloton warheads. Their updated guidance systems have a CEP of 100 meters. Trident submarine missiles were allowed to continue to carry up to eight warheads. Russia was required to make corresponding reductions.

Nature and Use of Nuclear Weapons

When a conventional explosive is detonated, it takes but a tiny fraction of a second for chemical reactions to turn the explosive into high-pressure gases. The subsequent rapid outward expansion of these superhot gases is the explosion. Rapidly occurring nuclear reactions can do the same thing, but because nuclear forces are one million times stronger than chemical forces, the energy released is one million times greater.

Nuclear explosive devices are difficult to make and involve two basic kinds of nuclear reactions: fission and fusion. The bombs dropped on Hiroshima and Nagasaki were fission weapons. In a fission chain reaction, neutrons strike nuclei of plutonium or uranium 235, causing them to split roughly in half. In doing so, they release two to three new neutrons, along with a great deal of energy. Uranium 235 is the isotope of uranium that has 92 protons and 143 neutrons in its nucleus. It fissions, or splits, more readily than the more common uranium 238, which has 92 protons and 146 neutrons. Isotopes that readily fission and sustain a chain reaction are said to be fissile. The most common fissile isotopes are uranium 235, which must be painstakingly separated from the far more abundant uranium 238, and uranium 233 and plutonium, which must be made in nuclear reactors.

For a nuclear explosion to occur, the chain reaction must be supercritical; that is, each fission must lead to more than one new fission. For example, suppose that each fission produced two neutrons and that each of these two neutrons produced two new fissions. If there were two fissions in the first generation, there would be four in the second, eight in the third and 2^N in the Nth generation. At this rate, every nucleus in 17 kilograms of uranium could fission in fewer than 85 generations. This would take less than two-millionths of one second.

The minimum amount of uranium required to produce an explosion is called the critical mass. Critical mass depends not only on the amount of material present but also on its shape and on the materials surrounding it. If there is less than a critical mass, too many neutrons escape from the uranium without producing fissions, and the process fizzles out. The critical mass of weapons-grade uranium-235 metal is 17 kilograms, if it is surrounded by a good neutron reflector. The critical mass of weapons-grade plutonium metal is only 4 kilograms, but that increases to 10 kilograms without a neutron reflector. A critical mass cannot be assembled before it is intended to explode, because a stray neutron produced by a cosmic ray could initiate an untimely explosion.

The atomic bomb dropped on Hiroshima on August 6, 1945, weighed 4.4 metric tons (9,700 pounds) and had a yield equal to 14.5 kilotons of the high explosive TNT. The yield was about 1.3 percent of the maximum possible yield for the amount of fissile material used. The core contained 60 kilograms of uranium 235, surrounded by 900 kilograms of uranium 238 to serve as a tamper and neutron reflector. The inertia of the tamper briefly slows the core’s expansion and allows a few more generations of fission to occur. To keep it below critical mass, a large segment of the uranium-235 core was removed and placed into a short cannon. When the Hiroshima bomb fell to 680 meters above the ground, the cannon fired the missing segment into the core. That action also mixed a small amount of beryllium and radioactive polonium 210, a combination that produced a flood of neutrons. Two-thirds of the city was destroyed in the explosion, and about 140,000 people were killed, either immediately or within a few months from injuries they sustained during the explosion.

The bomb that was dropped on Nagasaki on August 9, 1945, used plutonium, primarily plutonium 239. When plutonium is made in a nuclear reactor by adding neutrons to uranium 238, plutonium 240 and plutonium 242 are also formed. The latter two isotopes can spontaneously fission and produce too many neutrons to make gun assembly predictable. The Nagasaki bomb used 6.1 kilograms of plutonium in a noncritical configuration. This plutonium core was surrounded by 2,300 kilograms of high explosives. When the explosives were detonated simultaneously from all sides, the resulting implosion compressed the plutonium core to twice its normal density, thereby achieving critical mass. The resulting nuclear explosion had a yield of about 23 kilotons of TNT, 17 percent of the maximum possible yield for that amount of plutonium. About 70,000 people were killed either immediately or within a few months.

For several years weapons scientists speculated about building “the super,” in which light elements would be fused into heavier elements and give off a great deal of energy in the process. After the Soviets exploded their first atomic bomb in 1949, work on the hydrogen bomb, as it is now called, began in earnest. Edward Teller (born 1908) and Stanislaw M. Ulam (1909–84) had the key insight of how to use an atomic bomb to create the high temperature and pressure necessary for fusion.

Inside a 300-kiloton hydrogen warhead may be a uranium-238 cylinder about 1 meter long and 0.5 meter in diameter. Inside the cylinder at one end there is a small fission bomb about the size of a soccer ball that serves as a nuclear trigger. A fat rod of lithium deuteride (LD) lies along the cylinder’s axis with a slab of uranium 238 (the pusher) between it and the trigger. Deuterium is heavy hydrogen, and its nucleus is a proton-neutron pair. A thin plutonium rod (the spark plug) lies along the center of the LD rod, and the outside of the LD rod is covered with a uranium-238 tamper. The space around the rod is filled with plastic foam. The exploding trigger creates a pressure of 1 billion atmospheres and a temperature of 100 million Kelvins. X rays turn the foam into plasma while the outer uranium cylinder momentarily channels the energy and pressure onto the LD rod. As the rod and its plutonium core compress, neutrons cause the spark plug to fission, and then lithium fissions into tritium, a proton linked to two neutrons, and helium. Tritium and deuterium now fuse, releasing a tremendous amount of energy along with high-energy neutrons. These neutrons cause part of the outer uranium cylinder to undergo fission as it disintegrates. Hence this is a fission-fusion-fission weapon.

By 1964, the Soviet Union (1949), the United Kingdom (1952), France (1960), and China (1964) had all developed nuclear weapons. In an attempt to prevent further expansion, the Non-Proliferation Treaty (NPT) was negotiated in 1968. Although it was generally effective in discouraging further development of nuclear weapons, India, Israel, and Pakistan failed to sign the treaty and later acquired nuclear capability. Iran, North Korea, and Syria are widely regarded as supporting programs that might lead to the development of nuclear weapons.

During the Cold War, Warsaw Pact nations equipped and maintained an army twice the size of that of the defending North Atlantic Treaty Organization (NATO) forces. In an effort to make up for this imbalance, the United States deployed many tactical nuclear weapons with yields of about 10 kilotons or fewer. The most notorious of these was the neutron bomb, or Enhanced Radiation Weapon (ERW). One version was a projectile for an 8-inch howitzer (artillery gun) with a range of about 17 kilometers. A second version was a warhead for the Lance missile with a range of about 130 kilometers. These warheads were fission-fusion devices, small plutonium bombs containing tritium, with a 1-kiloton yield. The blasts of such warheads would destroy buildings within a radius of 760 meters (0.5 mile), and the neutron radiation would kill unshielded people at about twice that distance. Strategists argued that because these weapons caused less collateral damage than larger weapons, the Warsaw Pact nations would believe that they were more likely to be used and would be deterred from attacking. These weapons were kept ready for use for about ten years, after which they were included in the nearly 7,000 nuclear warheads and bombs retired at the end of the Cold War.

Development of Nuclear Strategies

World War II military strategists used the Nagasaki bomb to show that the Hiroshima bomb had not been a fluke and that more such bombs would be used if necessary. This ploy was partially a bluff, given that the next bomb would not have been ready to deploy until the end of August, 1945. However, the Japanese initiated surrender negotiations the day after Nagasaki was destroyed. Most historians agree that the use of these nuclear weapons probably saved more lives than they took, because they ended the war quickly and without the necessity of invading the Japanese homeland. Even as World War II ended, the Cold War with the Soviet Union had already begun. As the only nation with nuclear weapons, the United States could threaten to use them without fear of retaliation in kind. As the West disarmed, nuclear weapons were seen as a relatively cheap substitute for maintaining a large military force, and the United States began building a large nuclear stockpile.

Several years before the Western Allies believed it would happen, the Soviets exploded a plutonium bomb on August 29, 1949. In response, the United States developed the hydrogen bomb, first testing it in 1952. The Soviets tested a hydrogen bomb only one year later. To contain communism, the United States threatened “massive retaliation” if the Soviets committed unspecified aggression anywhere in the world. The Soviets could have been attacked from bomber bases in Europe or, after 1948, by intercontinental bombers based in the United States.

After the Soviets had developed a large number of nuclear weapons and its own intercontinental bomber force in 1955, the doctrine became “mutual assured destruction” (MAD). With each country able to destroy the other, neither could afford to try anything foolish. MAD required that the United States be able to absorb a nuclear attack by the Soviets and still deliver a devastating response. It was seriously proposed that nuclear missiles be placed on the Moon, because missiles aimed at the Moon would take days to arrive, and during that time, U.S. bombers could hit the Soviet Union. If, instead, the Soviets first targeted the continental United States, missiles from the Moon could be launched at the Soviet Union. A more practical course was taken by building up a triad of nuclear bombers, ICBMs, and submarine-launched missiles. It was judged that the Soviets could not destroy enough of the triad in a preemptive strike to escape overwhelming retribution.

Intercontinental bombers might take fifteen hours to reach their targets, and they could be recalled in case of a false alarm. ICBMs put a hair trigger on MAD, because they take only thirty minutes to reach their targets and, once underway, cannot be recalled. Missiles launched from nearby submarines might take only seven to fifteen minutes to reach their targets. As missiles became more accurate, warhead yield was reduced from multimegatons to between 100 kilotons and 475 kilotons, and a “counterforce” doctrine was introduced, in which the enemies’ armed forces, particularly their nuclear weapons, were targeted. In the belief that the Soviets were less likely to try something if they were more sure that the United States would not hesitate to respond, the doctrine of “flexible response” was advanced in the early 1980’s. This meant that, in place of MAD, the U.S. response would be commensurate with the scope of the enemy attack. Many found flexible response to be a very disturbing policy, because it made the use of nuclear weapons no longer unthinkable. They feared that any limited nuclear war would escalate into full-scale nuclear war. Fortunately, perhaps because of MAD, the nuclear powers have gone to great lengths to avoid directly fighting each other, and there has been no further use of nuclear weapons.

The nuclear stockpile of weapons in the United States peaked in 1966 at about 32,000, more than four times the number possessed by the Soviet Union. Soviet stockpiles peaked in 1986 at about 41,000. As a result of a series of agreements that began with the Strategic Arms Reduction Treaty I (1991), by 2009 those numbers had been reduced to about 10,000 in the United States (with 6,700 in reserve or waiting dismantlement) and 13,000 in Russia (with 8,100 in reserve or waiting dismantlement). These numbers tell only part of the story, however, as different types of nuclear weapons have varying yields of power.

With the election in the United States of President Barack Obama in 2008, new impetus was given to the reduction of nuclear arsenals. Speaking in Prague in April of 2009, Obama argued that the United States had “a moral responsibility to act” and committed America to “a world without nuclear weapons.” Among the steps he planned to pursue were negotiation of a new strategic arms reduction treaty with Russia, ratification of the Comprehensive Test Ban Treaty, and a new treaty ending production of weapons grade nuclear materials. Although none of these had been achieved by the end of 2009, his efforts gained worldwide attention and widespread international support. In bestowing on Obama the 2009 Nobel Peace Prize, the committee “attached special importance” to his “vision of and work for a world without nuclear weapons.”

Development of Missile Defense and Antiballistic Missiles

Thirty-six nations possess ballistic missiles of some type, and fifty-two nations have antiship cruise missiles. Doubtless, defenses against missiles have been sought ever since missiles became effective weapons. British fighter planes were able to shoot down some V-1’s, and the more daring pilots flew alongside, slipped a wing under the V-1, and then tipped it, confusing the V-1’s primitive autopilot and sending the missile into a dive. There was no defense against the V-2’s. In the 1982 Falkland Islands War, there was no defense when the HMS Sheffield was lost to a French Exocet cruise missile launched by the Argentinian air force. An Iraqi air force pilot flying a French-built Mirage fighter mistakenly launched two Exocets at the USS Stark in 1987. Thirty-seven sailors died, and twenty-one others were wounded. The Stark was protected by a Phalanx close-in weapon system (CIWS), but it failed to fire because of a tragic mistake: Because France was an ally, Exocets were tagged as friendly.

The Phalanx system is deployed on nearly all US Navy ships and in the navies of several allied nations. The Phalanx is a fast-reaction, rapid-fire 20-millimeter gun system. First deployed in 1978, current models fire 4,500 rounds per minute, although the magazine holds only 1,550 rounds. The rounds are hard and dense—they were originally made from depleted uranium but are now made of tungsten—and they fly at very high speeds. Their muzzle velocity is 1,113 meters per second, more than three times the speed of sound. The system uses radar and a forward-looking infrared (FLIR) detector to locate and track targets automatically. The FLIR is the ship’s last line of defense against incoming missiles and aircraft, and a recent upgrade allowed it also to engage small, fast-moving surface craft during both day and night.

The Avenger Pedestal-Mounted Stinger system can shoot down cruise missiles. It is mounted on a heavy high-mobility multipurpose wheeled vehicle (HMMWV). A gyro-stabilized turret gives it a shoot-on-the-move capability. The gunner’s turret has a .50-caliber (12.7-millimeter) machine gun and eight Stinger missile launch pods. It has a forward-looking infrared sensor, laser range finder, and a video autotracker. It can also receive tracking cues by radio from a nearby radar set, if one is available.

The Patriot missile was originally an antiaircraft weapon but was hurriedly modified in the mid-1980s to defend against ballistic missiles. A phased-array radar locates the target and directs the missile to it. As it nears the target, the missile homes in on radar waves reflected from the target, then a proximity fuse detonates a 90-kilogram, high-explosive warhead. At first the Patriot missile seemed to be very successful at stopping Iraqi Scud missiles during the Gulf War (1990–1991). Later analysis showed that many of the Scuds simply broke apart as they hit the lower atmosphere at high speed, and that the Patriot usefully destroyed some of the debris. Other Scuds were only knocked off course by Patriot explosions, but certainly the Patriot missile was at least a partial success. The Patriot missile and radar, upgraded to the Patriot Advanced Capability-3 (PAC-3), was scheduled to deploy alongside earlier Patriot missiles in 2012. Although slower than some earlier models, it has hit-to-kill capabilities, and can protect five times the area.

In March, 1983, US president Ronald Reagan gave dramatic impetus to the development of missile defenses with announcement of his Strategic Defense Initiative (SDI), with the “ultimate goal of eliminating the threat posed by strategic nuclear missiles.” This spawned a series of expensive and technologically unproven initiatives, including the creation of laser defenses, that led critics to dub the program “Star Wars,” after the fantasy film series of the same name. By 1993, the program was renamed Ballistic Missile Defense Organization (BMDO), and the emphasis had shifted from national to regional defense. Although a comprehensive global defense system was never developed, a number of the technologies emanating from the SDI were pursued and eventually deployed.

Testing of weapons using high-energy lasers has demonstrated the technology’s battlefield potential for combating missile attacks. Israel and the United States collaborated in developing a Tactical High Energy Laser (THEL) system, which was expected to be useful against short-ranged (20-kilometer) Katyusha rockets frequently employed against Israel by Hizbullah units. The system’s weakness against medium- and long-range missiles led to interest in various mobile systems (MTHEL), including the creation of a prototype of airborne units, unveiled in 2006. With funding for the MTHEL discontinued by the United States in 2004, its deployment became unlikely in the short term. The first generation of lasers required chemical reactions to produce high amounts of energy in a short period of time, usually burning ethylene with nitrogen trifluoride before adding deuterium. Studies suggested that effective MTHEL systems would require electrically produced lasers, which likely could not be deployed until the 2010s.

The Navy Area Theater Ballistic Missile Defense (TBMD) system was developed to protect U. and Allied forces and areas of vital national interest against theater ballistic missiles. The lower-tier defense uses Aegis cruisers and destroyers, which have phased-array radars and battle management computers that can simultaneously detect and track more than one hundred targets. Incoming enemy missiles are intercepted with the Standard Missile (SM)-2, which has a range of 185 kilometers. Missiles slipping through that defense are then engaged by the Phalanx system. As a result of massive cost overruns in perfecting radar and SM-2 Block IVA capabilities, the Department of Defense canceled the program in December, 2001, though upper-tier defense uses the Terminal High Altitude Area Defense (THAAD) system’s long-range, hit-to-kill interceptor, which was first activated in 2008. Surviving enemy missiles aimed at ground targets are then engaged by the Patriot (PAC-3) system. Arrow-2 is a two-staged interceptor developed jointly by the United States and Israel. It uses a blast-fragmentation warhead to destroy enemy missiles and has a range between those of the Patriot and the THAAD interceptor. It could be employed by the United States if deemed necessary.

The lower tier of the theater missile defense systems seems to be well founded. The upper-tier THAAD interceptor is less well developed, and the National Missile Defense (NMD) system is even further from deployment. The first attempt at an NMD was the Safeguard antiballisticmissile system. It used longer-ranged (748 kilometers) Spartanmissiles with 5-megaton warheads and shorter-ranged (40 kilometers) Sprintmissiles with low-kiloton yield warheads. The Sprint warheads were enhanced-radiation devices intended to cripple incoming warheads with neutron radiation. Unfortunately, they had a fatal flaw—the first few nuclear explosions destroying incoming missiles would have blinded the acquisition and tracking radar. The system was built despite the known flaw, but it remained active for only four months in 1976.

An ABM system can attack missiles as they rise through the atmosphere (boost phase) and are most vulnerable; as they coast through space (mid-course phase), when decoys are the most effective; or as they plunge back into the atmosphere over the target (terminal phase), when time is short. The boost phase lasts from three to five minutes; the mid-course phase, up to 20 minutes; and the terminal phase, about 1 minute. To maintain enough assets in orbit to destroy a massive attack during launch would be prohibitively expensive. In fact, since MIRVed warheads and decoys are cheaper than antiballistic missiles and their support system, it is cheaper to overcome an ABM system with a massive attack than it is to build an ABM system extensive enough to stop a massive attack.

However, it might be practical to stop a limited attack. Such an attack might be a missile, or a few missiles, launched by a renegade military commander or by a rogue nation. Although none of these scenarios seems likely, any of them could kill thousands of people or many more. This fact makes it worthwhile to at least consider a defense against them. In the quarter century since the development of the Safeguard system, technology has advanced to the point that it is now possible “to hit a bullet with a bullet”; however, current systems are more effective against shorter-ranged missiles than they are against longer-ranged missiles.

If built, the National Missile Defense system would have several elements. Large, phased-array surveillance radars would detect and track missiles aimed at the United States. X-band radar has a shorter wavelength than normal radar and can therefore see finer detail. Ground-based X-band radar would be used to track targets and discriminate against decoys. Infrared sensing satellites already in orbit monitor the Earth to detect the hot exhaust gases of missile launch. This system was used to detect Scud launches during the Gulf War. The Space-Based Infrared System (SBIRS) would be an expanded and modernized version of the current system. It would acquire and track the missiles shortly after launch and provide the greatest warning. The system’s weapon component is the Ground-Based Interceptor (GBI), a missile always kept ready to launch a Kill Vehicle (KV) into space. The KV would have its own sensors, propulsion, communications, and guidance systems and would maneuver to the target, distinguish decoys, and destroy the target in a high-speed collision. Concern over the possibility of attacks from rogue states and terrorist groups led to continued government funding of SBIRS, despite its prohibition by the Anti-Ballistic Missile (ABM) Treaty signed by the United States and Russia in 1972. The United States unilaterally withdrew from the treaty in 2002.

Turning Points

1792

• War rockets are used by the sultan of Mysore to terrorize British soldiers.

1805

• British artillerist William Congreve develops the first warfare rockets and launching tubes.

1846-1848

• Hale rockets, an improvement on Congreve rockets with metal vanes in the rockets’ exhaust, are used in the Mexican-American War.

1926

• Robert Goddard achieves the first free flight of a liquid-fueled rocket.

1945

• The world’s first atomic bomb is exploded near Alamogordo, New Mexico.

1952

• The world’s first hydrogen bomb is exploded at Enewetak Atoll in the Pacific Ocean.

1983

• U.S. president Ronald Reagan announces plans to pursue a Strategic Defense Initiative (SDI) designed to provide space-based defense against nuclear missile attacks.

1987

• US president Ronald Reagan and Soviet general secretary Mikhail Gorbachev sign the Intermediate-range and shorter-range Nuclear Forces (INF) treaty, the first arms treaty to actually reduce the numbers of nuclear weapons instead of merely limiting their growth.

2002

• The United States withdraws from the Anti-Ballistic Missile (ABM) Treaty.

2009

• US president Barack Obama is awarded the Nobel Peace Prize, with special reference to his “work for a world without nuclear weapons.”

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