4
Targets and Targeting
On the morning of August 6, 1945, Hiroko Fukada was holding her baby in a crowded Hiroshima streetcar. It was hard to get transport in the early morning and the car was packed full. All of a sudden there was a flash, and an explosion shattered the windows of the car. Hiroko was cut by the flying glass, but she was not seriously injured. Many of those around her were slumped down dead. She looked down at her son, and saw that his head had been punctured by a piece of flying glass. He smiled up at her bloody face. She would always remember the smile. He died later that day.
Taeko Teramae was waiting outside her school when she saw a shiny object descending through the sky. She thought that it was very pretty. There was a flash and a bang and she was thrown to the ground. A slimy grit filled her mouth and she threw up. In a few moments she stood and realized that she did not seem to be hurt. But many around her were staggering around in tattered and burned clothing. Much later, she found a piece of mirror and held it to her face. Her eyes were swollen, her skin red. She was afraid that she had become a monster.
Kinue Tomoyasu saw her daughter off to work and went back to bed. There was an air-raid warning, and after the all-clear sounded, she got up, put away her bedding, and went to the window to look outside. There was a flash, and she found herself on the opposite side of the room. The window had blown out and glass was everywhere. From the direction of the flash, Kinue knew that the explosion came from the center of the city, near where her daughter worked. She dressed, swept up the glass, and set out to find her daughter. As she came into the city center, she passed hundreds of injured people, and many dead bodies. She searched and searched until a neighbor told her that her daughter was down by the riverbank. The pretty young woman was a mass of burns, and maggots were already in her wounds. It was too painful to pick them out. The mother held the daughter in her lap, calming her and telling her to hold on. “I don’t want to die,” the young woman cried. She lasted another nine hours. Going home, Kinue Tomoyasu was caught in a black rain. Sometime later her hair began to fall out and purple blotches appeared on her skin. She lived to old age.
The stories of the survivors of Hiroshima, taken from atomicarchive.com, have a sad similarity. There were the three colors: the yellow flash, the redness of the fires, the black rain bringing deadly fallout. Time itself seemed to skip several seconds—people remember standing by a window or in the street, and the next thing they knew they were lying down many yards away. And the noises. A bang from the blast, the crackle of flames, the rumble of collapsing buildings. All around, the injured called, “Mother! Mother!”—something that people sometimes do when they know that they are going to die.
THERE IS RELUCTANCE by some to use the word “target” in discussions of nuclear weapons. We removed targeting data from missile guidance computers at the end of the Cold War, a confidence-building measure with Russia, even though both sides knew it took only a few moments to reload the data. “Targeting” is taken by some to be equivalent to saber rattling, a needless provocation. But nuclear weapons are not ethereal objects of international diplomacy—they are capable of inflicting enormous damage. Within each target circle of the nuclear war planner’s maps are hundreds of thousands of Hirokos, Taekos, and Kinues.
There are two approaches to nuclear targeting: countervalue and counterforce. Countervalue targeting aims to destroy cities, populations, and other things of value so as to shock the enemy into ceasing hostilities. It is typically employed by countries that have several hundred nuclear weapons (or fewer) and a limited number of missiles or aircraft with which to deliver them. Although few governments advertise that their nuclear weapons are aimed at heavily populated cities, most are forced into this position by the lack of accuracy of their missiles, which makes them ineffective against hardened military targets.
Counterforce targeting, on the other hand, aims to eliminate the adversary’s capability to inflict further damage on your side. It involves targeting military bases, missile fields, submarines, and other targets of strategic value, and it tries as much as possible to avoid damage to population centers. In the case of the Soviet Union, many key assets of military command and control were located in and around the Moscow region, so such distinctions were more technical than practical—large numbers of people would have been killed in either strategy.
In any type of armed conflict, the type of weapon chosen for a particular mission depends on the target that is being attacked. For example, if the target is a single individual at close range, a pistol will suffice, but if the target is a tank, then pistol shots would merely bounce off, and an armor-piercing round is required. If the target is a tunnel complex deep underground, then conventional high explosives will have no effect, and the only means of destroying it is with a nuclear weapon.
We divide likely targets for nuclear weapons into four categories:
Soft point targets, such as mobile missile launchers that might contain weapons of mass destruction. These targets are easily destroyed with minimal explosive force, but they may be difficult to find against the clutter of other vehicles, buildings, forests, and so forth.
Soft area targets, such as air bases, army posts, and naval shipyards. These targets can be destroyed by conventional explosives, but they are so large that huge quantities would be required.
Hard point targets, such as missile silos and command and control bunkers. Targets in this category are designed to withstand almost any attack with conventional high explosives.
Super-hard targets, such as facilities buried under mountains. Such targets include command and control facilities, manufacturing sites for weapons of mass destruction, and safe refuges for government leaders. When a facility is buried under a thousand feet or more of hard rock, even nuclear weapons might not cause significant damage.
Before going into detail on each type of target, we need to discuss how nuclear weapons damage their targets and how much damage might be expected for a given weapon yield. Whereas a conventional bomb or artillery shell causes damage by means of a blast wave or shrapnel generated during the explosion, most of the energy of a nuclear weapon—about 80 percent—is released in the form of x-rays. The remaining 20 percent of the energy of the bomb is emitted in neutrons, gamma rays, and only a small fraction in the form of “hydrodynamic” or blast energy. The intense blast waves seen in films of nuclear explosions are actually produced when x-rays, neutrons, and gamma rays are absorbed in the air or ground.
One of the distinguishing characteristics of a nuclear weapon is the radioactive fallout generated by the nuclear reactions in the explosion. The effects of a conventional weapon are over with the explosion itself, but the effect of a nuclear weapon can linger for months, years, or even decades. During the fission process—the means by which most of the energy of a weapon is generated—uranium and plutonium nuclei break into pieces. These smaller nuclei are often radioactive in their own right, emitting damaging radiation over time. When a weapon is detonated at high altitude, above where the nuclear fireball would touch the ground, a weapon’s radioactive fallout is limited to that produced by its own materials and whatever elements in the atmosphere might be “activated” by the bomb’s radiation. Since this is a relatively small amount of material, it is quickly dispersed by winds and spread over a wide area, producing some long-term health effects but few immediate casualties from fallout.
A much bigger problem occurs when the weapon is detonated at the surface of the earth or at low altitude where large amounts of soil are swept up by the blast wave and activated by the lingering nuclear reactions in the mushroom cloud. This is illustrated in the figure above. Not only are more atoms activated, but more types of atoms are affected, atoms that can produce long-term radioactive effects on people and the environment. Curiously, it is not the most radioactive elements that are the biggest problem, since they decay relatively quickly. The greater concern is with radioactive nuclei that take years or decades to decay, making habitation of the target zone unhealthy for prolonged periods. However, it is incorrect to assume that a nuclear explosion will render an area forever un-inhabitable. Both Hiroshima and Nagasaki are thriving cities today, and even the Nevada Test Site, the location of one hundred atmospheric test explosions, has recovered to the point where it is difficult to tell where the tests occurred. Only the twisted wreckage of test equipment is a clue to the enormous energy released. (The situation is different in the Marshall Islands, some of which were used for high-yield atmospheric nuclear testing. Low levels of radioactivity in the soil are concentrated by growing plants and trees, contaminating potential food sources used by the residents.)
While the effects of residual radiation may be subtle, they are not entirely absent. When scientists wanted to construct an experiment to measure very low levels of radiation from natural sources, they found that their results were spoiled by nuclear test contamination in the steel in their apparatus. Searching the world for a pure enough material, they found the rusting hulks of World War I German battleships scuttled at Scapa Flow in the north of Scotland. These ships were constructed before nuclear testing, and with the protection of the ocean, they were unsullied by radioactive fallout.
Nuclear weapons produce other effects beyond blast and radiation. The intense heat resulting from a nuclear explosion can start fires over large areas in a city or a forest and cause severe burns on people. Military planners refer to this as a “secondary effect” and often do not consider it in their calculations of damage. The flash of light from the explosion can cause temporary or permanent blindness. Observers of early atomic tests conducted in the atmosphere wore thick welders’ goggles to avoid eye damage as they watched the flash and ensuing mushroom cloud.
When a nuclear explosive is detonated at very high altitude, above several tens of miles, an electromagnetic pulse is produced, directed toward the ground. The mechanism is simple: Gamma rays from a nuclear explosion travel downward and collide with atoms in the atmosphere. During these collisions the gamma rays knock an electron from the atom, producing an electrical current, much like the electrical current in a radio-transmitting antenna. And, just like the current in an antenna, the current generated by the gamma rays produces a radio signal. This radio signal can disrupt or even destroy sensitive electronic equipment such as computers and communication systems.
Since an electromagnetic pulse (EMP) is generated in the upper atmosphere and projected downward, the affected area from such an attack is quite large, potentially encompassing an entire country. However, the consequences of such an attack are limited to electronics (people and structures are not affected), and there is considerable debate within the scientific community about the sensitivity of electronics to a given type of pulse. Contrary to media reports, it is not true that an EMP attack from a typical strategic weapon would completely shut down the electronics within a country. First, the effect is statistical in nature—some systems will not notice the pulse at all while identical counterparts will be affected. Second, the most likely effect from an EMP attack is “upset” rather than destruction, that is, a temporary scrambling of the memory of a computer or the frequency of a communication device, something that is easily corrected by rebooting or resetting the device. (Upset can, however, have catastrophic consequences if the computer is the flight controller of an aircraft or another time-critical system.) Third, the EMP output from a typical device is degraded by several design issues so that few, if any, weapons currently deployed in military stockpiles will produce the maximum possible effect. Of all the nuclear effects, EMP seems the most prone to misunderstanding and misinterpretation.
Yet another effect can happen when a nuclear explosion occurs in low earth orbit where many communication satellites operate. The explosion of the weapon produces a burst of electrons, which are captured in the magnetic field of the earth, greatly contributing to the naturally occurring radiation pattern that satellites must endure. Even a relatively small nuclear weapon—one with a yield of ten kilotons—could produce enough radiation to destroy many satellites, interrupting vital communications around the world.
The area that is affected by a nuclear weapon depends on the type of nuclear device used, its yield, and the hardness of the target. While most nuclear weapons in military stockpiles produce the greatest fraction of their energy in the form of x-rays, some are optimized for generating intense bursts of neutrons, so-called neutron bombs. These weapons have a smaller blast effect, but their neutrons are lethal to people, animals, and other biological organisms. They are designed for use against massive tank formations, since they kill the tank crews with less damage to the surrounding countryside.
The yield required for a nuclear mission, and the precision with which the weapon must be delivered, depends on the hardness of the target. Suppose that the target is a missile silo with a door constructed of ten feet of reinforced concrete. A few tons of nuclear yield—a so-called micronuke—might not cause enough damage to destroy the cover, meaning that the enemy could still fire its missile. A ten-kiloton nuclear explosion would need to be on top of the silo to assure its destruction, but a one-hundred-kiloton explosion could be a few hundred feet away. The yield required for destruction does not simply scale with distance—the energy of an explosion is sent in all directions, so the effect decreases as the inverse cube of the distance; to have the same effect twice as far away, an explosive has to be eight times as powerful. This is an illustration of the importance of accuracy—more accurate missiles allow much smaller explosives to be used. We have seen this in conventional warfare when a single precision bomb has destroyed targets that formerly would have required massive heavy bombing with destruction over a wide area.
If the desired outcome is to cause massive destruction to a soft target such as a city, one would detonate a nuclear explosion at an “optimum height of burst” to allow the shock wave and fire-starting potential of the weapon to impact the largest area. Detonating at too low an altitude would cause most of the weapon’s energy to be diverted into making a crater, while too high a burst would dissipate its energy into the atmosphere without producing damage on the ground. The radius of effect for soft targets is much greater than for hard targets because much less energy is required to produce damage to relatively fragile structures.
We now turn to each of the four types of targets and discuss what weapons would be most suitable for destroying them or, in military parlance, “holding them at risk.” Particular attention will be given to changes in strategic thinking made possible by improvements in the accuracy of the delivery vehicle.
Soft Point Targets
The destruction of soft point targets is taking on much greater importance as more countries acquire SCUD missiles and other mobile missile systems that can carry weapons of mass destruction. The launchers for these missiles are typically very fragile so that only a small explosion is required to render them inoperable, but they are difficult to find, and once located, they can move faster than aircraft can be directed to their location. Also, any attack on a missile containing a chemical, biological, or nuclear warhead poses the danger that the warhead could explode, releasing its contents over an area that might contain population centers or that might be later occupied by friendly forces. This is a case where more explosive force may create a bigger problem than existed previously. Maybe the missile would have been used, maybe not, but an attack with a sizable explosive force would certainly cause the release of deadly material or even the detonation of a nuclear warhead.
The accuracy of missiles during most of the Cold War was so poor that a large explosion had to be used to assure the destruction of even a soft point target. If you could be sure only that a warhead would land within a mile of its target, then the amount of conventional explosives required to destroy it would have been much greater than the payload capacity of even the largest missile. While a small nuclear yield might have sufficed, the complexity of maintaining many different types of weapons in the stockpile led to the use of standard high-yield designs, even though their immense destructive force was unnecessary.
The situation today is different in several fundamental ways. First, our ability to locate and track mobile targets is vastly better than it was even twenty years ago. The development of integrated command and control systems, tied directly to signals from satellites, unmanned aerial vehicles, and observers on the ground, means that weapons can be directed in real time with a high probability of target destruction. Second, the improved accuracy of weapons delivery means that we can now target not just a mobile missile launcher, but a particular part of that launcher, reducing the probability of an explosion that would release harmful materials. Hitting the firing controls, the launch rails, or other vital components would render the missile inoperative. Even though the warhead would remain intact, it would be useless without a missile to deliver it. Once our forces advanced to its location, it could be safely transported and destroyed.
A very small explosion—or even the impact of a high-velocity round that doesn’t contain any explosives at all—can actually be more effective against a biological weapon than a low-yield nuclear weapon. The reason is that a minimum-force approach has a higher probability of containing the bio-weapon, whereas a nuclear explosion will spread it around the countryside, often without killing the agent itself. There have been a number of articles in the press that advocate the development of “mini-nukes” for attacking biological and chemical weapons, but in fact these are the last weapons that one would want to use against such targets since they assure the widest dissemination of the deadly material.
A potentially more serious result of using a nuclear weapon against a chemical or biological target is that it makes the user the first to cross the nuclear threshold. Since their first use against Japan, nuclear weapons have been put into a special category—they are not like other weapons. They are capable of destroying a city, a country, or even civilization itself in a matter of hours. Once the nuclear genie is out of the bottle, once a country has crossed the threshold to use nuclear weapons, other countries may infer that they are justified in using their own nuclear weapons. This could lead to the escalation of a conventional war to a global thermonuclear catastrophe. It is unlikely that using a small nuclear weapon would make a difference—nuclear is nuclear, and the political and military consequences of its use are unpredictable.
Nonnuclear weapons are thus more effective than nuclear weapons against chemical or biological targets. The use of existing guidance packages in precision bombs, enhanced by automatic image recognition and self-targeting in the terminal stage, enables nonnuclear munitions to be very effective in this mission. In this case, most or all of the explosives would be removed from the bomb and new electronics would be installed to enable it to hone in on the desired part of the target.
Similar technology could be used in ballistic missile warheads, including those fired from intercontinental distances. Here the problem is more complicated since the high velocity of the warhead falling from space would cause significant damage even without any explosive payload. However, warhead speed can be reduced by means of retro rockets or deployable flaps so that the force of impact would be greatly reduced.
The biggest problem in attacking soft point targets is accurate intelligence. If we know where the target is, we can destroy it. If we don’t know where it is or, worse, don’t know that it exists, then even a high-yield nuclear weapon will not assure its destruction.
Soft Area Targets
Some targets are very large—airfields, naval bases, and troop deployments can cover hundreds of square miles. Nuclear weapons were assigned to these targets for two reasons. First, the quantity of conventional high explosives required to destroy them was so great that hundreds of bombers would have been needed for its delivery. Precision conventional weapons could put a runway out of action for a few hours, but they could not be delivered in sufficient numbers to eliminate the target as a future threat.
Second, air defenses would have made it difficult or impossible to get the required number of bombers over the target. Only nuclear explosives could be delivered in sufficient numbers and certainty to assure the destruction of large-area targets.
However, the most efficient way to destroy large targets is not via a single big explosion, but by detonating several much smaller ones distributed over the area. This is illustrated in the above figure, which shows the area damaged by several small weapons versus that of one large weapon—less total yield is required for distributed blasts than for one large one. To better understand this, think of how you might illuminate a very large auditorium—it is much more efficient to use many small lights scattered across the room than one very powerful one in the center. During the Cold War, high-yield weapons were planned for use against large soft targets not only because we didn’t have enough missiles to carry many small warheads, but because we didn’t want to maintain too many types of warheads—each of which would have required its own store of spare parts, its own trained maintenance crews, and its own set of delivery vehicles. Today, thanks to strategic arms reduction agreements, we have a surplus of missiles, more than enough to change our nuclear targeting policy to one that relies on the smallest weapon consistent with the mission. And we are finding that small weapons will suffice for most missions, allowing us to switch from mainly high-yield attacks to those involving much smaller weapons.
The effect of a nuclear detonation in a city depends on the yield of the weapon, where it is detonated, and the types of structures around it. The greatest damage occurs when the explosion occurs several thousand feet up—in that case the blast is spread over the widest area. Some of the force of an explosion at ground level is absorbed in nearby buildings that shadow those farther away from the full impact of the blast. However, channeling of the pressure pulse by urban canyons can complicate any predication of weapon effects. For a city consisting of nominally constructed many-storied buildings, a ten-kiloton explosion would produce severe damage over a quarter-mile radius. A one-hundred-kiloton explosion would cause the same level of damage over more than a half-mile radius, and a megaton blast would reach out to a mile and a half. Based on experience from the attacks on Hiroshima and Nagasaki, fifty thousand to one hundred thousand people would die from a ten-kiloton explosion, and correspondingly more for higher yields.
Hard Point Targets
Hard point targets include missile silos and hardened bunkers that are impervious to anything but a massive nearby explosion. During the second Iraq War, United States forces found that Iraq had built facilities underneath palaces and other civilian structures, “buildings within buildings,” with roofs and walls many feet thick. Sometimes the structure was designed with multiple layers of concrete, interspersed with air gaps, to cause bombs or warheads to explode well away from the sensitive part of the facility and to diffuse their energy into the surrounding decoy structure. While aerial observers would see destruction, the actual facility would continue to operate.
Nuclear weapons were assigned to this type of target during the Cold War because it was impossible to deliver a sufficient conventional explosive force to assure destruction. To avoid having to maintain many types of warheads, it was typical to assign a much higher-yield weapon to the target than was actually required to destroy it. Another factor encouraging high yield was uncertainty in the construction of the target; an enemy seldom cooperates in providing blueprints of its facilities, so overkill by a factor of two or more was often used to increase confidence that the target would be eliminated.
Advances in weapons technology have made the use of massive explosive force unnecessary in many but not all cases. For example, the capability to place a warhead on the cover of a missile silo is no longer beyond our reach. While the amount of conventional explosive that such a warhead could carry is still less than that needed to destroy the silo, the nuclear yield required is only a few percent of that which was formerly thought to be necessary. In fact, a ten-kiloton warhead is more than adequate to cause fatal damage to the silo if placed with sufficient precision.
Many missile fields contain a number of silos connected to a central command and control facility. To destroy all of them would require one low-yield nuclear weapon per silo. One might think that accurate intelligence and guidance might enable us to destroy the command center that launches the missiles rather than each individual missile, but it is still possible that the missiles could be fired remotely, or from the silo itself. High-yield nuclear weapons may not be able to do much better than low-yield ones, since in some cases the silos were deliberately placed far enough apart that a single high-yield explosion would not destroy more than a few, leaving the rest operational and ready for a retaliatory strike. If nuclear weapons are required, then lower yields will do as well as higher ones—it is a matter of the number of weapons, not yield.
Super-hard Targets
Several facilities around the world are so hard that even a high-yield nuclear explosion may not destroy them. For example, the United States announced that it suspected Libya of constructing a WMD facility under a mountain with hundreds of feet of rock and dirt protecting its critical components. The technique used was simple: Readily available tunneling machines were used to bore a horizontal shaft into the mountain, and once they were far enough inside, the tunnel was expanded to make rooms, some of which were large enough to handle manufacturing equipment, military command posts, and weapons storage. The required mining technology for these operations is relatively inexpensive thanks to advances in civil engineering and highway construction.
Even a very large nuclear explosion—say one in the megaton range—would still not destroy a deeply buried target if its builders took certain precautions. The tunnel could be lined with hardened concrete to prevent cave-ins, and sensitive equipment could be mounted on springs to absorb shocks. This technique was used in the Cheyenne mountain control complex in Colorado, where entire buildings were built on shock absorbers to ride out a nuclear attack. Similarly, the effect of a detonation outside the entrance would be greatly attenuated if the builder put a number of twists and turns into the tunnel, each protected by a heavy blast door. Shock waves from the nuclear explosion would lose some of their energy every time they had to “turn a corner” and penetrate a blast door. Even a direct hit on the tunnel mouth would not destroy a cleverly designed facility constructed deep within the mountain.
Super-hard targets are, at first glance, impervious to even nuclear weapons. However, there are some techniques that can enhance the effectiveness of a nuclear explosion without increasing its yield. Most prominent among them are the so-called earth-penetrating weapons that bury the nuclear explosive in several feet of earth before it is detonated. Even this shallow burial increases the coupling between the output of the weapon—which is mostly in the form of x-rays—and the ground. If the weapon were detonated in the atmosphere or on the surface, then at least half of its energy would be directed upward—wasted for the purpose at hand. When the weapon is covered with enough earth to trap the x-ray energy, then much more of its energy is directed downward into the earth. The increase in efficiency could be a factor of ten or more, reducing the need for high yield or, conversely, enabling a given yield to destroy a much deeper target.
There is one remaining possibility for eliminating a super-hard target, and that is to isolate it from any contact with the outside world. No facility is built to exist in absolute isolation. Some require extensive communication connections to enable them to control military forces, while others require easy entry and egress to deploy the weapons inside them. By destroying these communication links or burying the tunnel exits, it would be possible to render the facility at least temporarily inoperative. If the intent is only to provide short-term incapacitation, then these techniques will suffice and can be achieved with conventional explosives, including those placed on ballistic missiles. However, caution must be exercised, since some exits from the facility may be hidden and there may be many redundant cable connections to the outside world. Attacks with conventional weapons may achieve some damage, but it might be impossible to determine the effect of that damage until it is too late.
IT SHOULD BE clear from this discussion that the type of weapon required for a given mission depends on the target. Small targets that are sensitive to damage—such as mobile missile launchers—can be destroyed with very little energy. Very hard targets, or those that cover large areas, require more energy. The principal determinant of success in future strategic engagements may not be the absolute power of our weapons but the accuracy of our intelligence and our ability to deliver small weapons with precision.