On July 8, 1962, the United States detonated a 1.4-megaton hydrogen bomb approximately 250 miles above Johnston Island in the Pacific Ocean. Hundreds of miles away in Honolulu street lights went out, power lines shut down, circuit breakers popped open, and burglar alarms began ringing. The cause involved a somewhat esoteric effect of nuclear explosions at high altitudes, with very down-to-earth consequences - the generation of an extremely powerful, short-duration pulse of electromagnetic energy. The potential chaos which an electromagnetic pulse (often referred to as EMP) can unleash in a nuclear war includes the possible crippling of the military's ability to control and communicate with its strategic nuclear forces.
A nuclear weapon must be exploded above the atmosphere, preferably at a height greater than 40 miles, to produce a significant effect over a large area. The higher the explosion, the larger the ground area radiated with electromagnetic energy. A weapon with an explosive force of one megaton detonated at a height of 300 miles above the central US would bathe the entire continental US as well as parts of Canada and Mexico with electric fields large enough to damage most modern unprotected electronic systems.
Although the Pentagon has been aware of this effect for 20 years, almost a decade passed before the problem began to be seriously addressed. It is seen as all the more urgent now in light of rapidly changing electronics technology. At the time of the Johnston Island blast in 1962, most electronic circuitry still relied on vacuum tubes, which are a million times more resistant to this type of pulse than modern solid state electronics.
Today, however, the electronics revolution has made vacuum tubes almost obsolete, and their replacement by sensitive solid state circuitry has left many systems vulnerable to electromagnetic pulse. If a system with susceptible interior electronic components receives enough energy from the pulse, it may suffer either permanent damage or temporary impairment. The extent of electronic disruption may be widespread. The US is covered by a vast array of efficient collectors of electromagnetic energy: a huge grid of cables for power and telephone lines, metallic support towers, antennae, wiring, aluminum aircraft bodies, railroad tracks, and other unshielded metallic objects.
In a full-scale nuclear exchange, such damage to electronics will be the least of everyone's problems. Why then bother to worry about it at all?
One major reason for concern is the significant military problem raised by the potential disruption of the command, control, and communications systems which must direct the nation's arsenal in time of war. In response to this, the military has undertaken a major program of hardening control systems and communications links. New weapons systems, such as the MX missile and B-1 bomber , are designed with the electromagnetic pulse taken into consideration. Similarly, small self-contained systems such as satellites can and have been hardened.
In spite of these measures, much of the current command and control system remains vulnerable to electromagnetic pulse and will be so for some time. It is simply too huge a task to harden effectively the sprawling network of cables, towers, computers, airplanes, and so on, that comprise the US command and control system. For example, many of the airborne command posts which would play a vital role in directing ground forces and submarines during a war are not pulse-resistant. The Joint Chiefs have recently asked that more be hardened.
Since atmospheric testing is banned, various kinds of simulators have been built to test the effects of an artificial pulse on airplanes, missiles, and other systems that might be threatened. However, several problems exist: an exact pulse environment cannot be produced, and its interaction with mechanical structures or electrical circuits is strongly dependent on factors unique to each situation. Thus, although individual components or circuits may be tested, it is often difficult to predict how the entire integrated system will respond to an actual high-altitude explosion.
These difficulties underscore the uncertainty in predicting the response of systems during a nuclear war. One result may be a lessening of stability. Vulnerabiliy of command and central networks, whether real or perceived, may lead to an unbearable pressure during a crisis to use one's forces before control over them is lost. In providing a reliable deterrent, it is not enough for a weapons system itself to be invulnerable; although submarines themselves may be difficult to locate and destroy, their communications links are far more vulnerable and are the weak link in our sea-based deterrent.
Electromagnetic pulse does not affect only command and control; it presents a possible civil defense threat as well. Any civil defense program would have to contend with the probable blowout of radios and televisions, the sporadic shutdown of commercial telephone lines, and power outages throughout the country. The chaos induced by the disruption of communications and power (even in areas that have not been attacked) is likely to create havoc with any evacuation plans.
Most urgently, the problem of command and control vulnerability forces us to reex-amine current US strategic policies that emphasize the ability to conduct selective nuclear strikes over a protracted period. While huge expenditures on hardening might help, effectiveness of command and control during a nuclear war - above all, a protracted nuclear war - would still be uncertain. In light of this, it is doubtful whether the present US strategic policy represents a realistic course.
In these respects, electromagnetic pulse serves as one example of a general rule: it is simply impossible to predict with any (generally agreed upon) reliability how systems, people, and strategies will function during a nuclear war. Any policy which relies too heavily on the precise and coordinated interplay of people and systems over any period of time is dangerously misdirected.