The topic of nuclear electromagnetic pulse (EMP) is very mysterious to most people, and it is quite commonly misunderstood. It is also the subject of a large amount of misinformation. (It is a serious and persistent problem that many people want to ignore the science and make it into a political issue; or even worse, into a matter of Hollywood fantasy.) There are many additional EMP pages on this site, including separate pages on EMP personal protection, Soviet nuclear EMP tests in 1962, and on other EMP related topics including a separate page of notes and technical references. There is also a very important page about widely-believed EMP myths and a Site Map of EMP Pages on this web site. Much of the information here describes the possible effects of EMP on the continental United States, but the information can be used to describe the effects on any industrialized country.

In testimony before the United States Congress House Armed Services Committee on October 7, 1999, the eminent physicist Dr. Lowell Wood, in talking about Starfish Prime and the related EMP-producing nuclear tests in 1962, stated,

"Most fortunately, these tests took place over Johnston Island in the mid-Pacific rather than the Nevada Test Site, or electromagnetic pulse would still be indelibly imprinted in the minds of the citizenry of the western U.S., as well as in the history books. As it was, significant damage was done to both civilian and military electrical systems throughout the Hawaiian Islands, over 800 miles away from ground zero. The origin and nature of this damage was successfully obscured at the time -- aided by its mysterious character and the essentially incredible truth."

The Sky After the Starfish Prime Nuclear Test
from nearly 900 miles away

Although nuclear EMP was known since the very first days of nuclear weapons testing (and often caused problems in the local area -- especially with monitoring equipment), the magnitude of the effects of high-altitude nuclear EMP were not known until a 1962 test of a thermonuclear weapon in space called the Starfish Prime test. The Starfish Prime test knocked out some of the electrical and electronic components in Hawaii, particularly in Honolulu, which was 897 miles (1445 kilometers) away from the nuclear explosion. The damage was very limited compared to what it would be today because the electrical and electronic components of 1962 were much more resistant to the effects of EMP than the sensitive microelectronics of today. Also, the Starfish Prime warhead was very inefficient at producing EMP.

The magnitude of the effect of an EMP attack on the United States, or any similar advanced country, will remain unknown until one actually happens. Unless the device is very small or detonated at an insufficiently high altitude, it is likely that it would knock out the nearly the entire electrical power grid of the United States. It would destroy many other electrical and (especially) electronic devices. Larger microelectronic-based equipment, and devices that are connected to antennas or to the power grid at the time of the pulse, would be especially vulnerable. Deliberate regional attacks, using lower altitude nuclear detonations, are also possible.

The Starfish Prime test (a part of Operation Fishbowl) was detonated at 59 minutes and 51 seconds before midnight, Honolulu time, on the night of July 8, 1962. (Official documents give the date as July 9 because that was the date at the Greenwich meridian, known as Coordinated Universal Time.) It was considered an important scientific event, and was monitored by hundreds of scientific instruments across the Pacific and in space. Although an electromagnetic pulse was expected, an accurate measurement of the size of the pulse could not be made immediately because a respected physicist had made calculations that hugely underestimated the size of the EMP. Consequently, the amplitude of the pulse went completely off the scale at which the scientific instruments near the test site had been set. Although many of the scientific instruments malfunctioned, a large amount of data was obtained and analyzed in the following months, especially from equipment in more distant locations.

When the 1.44 megaton W49 thermonuclear warhead detonated at an altitude of 250 miles (400 km), it made no sound. There was a very brief and very bright white flash in the sky that witnesses described as being like a huge flashbulb going off in the sky. The flash could be easily seen even through the overcast sky at Kwajalein Island, about 2000 km. to the west-southwest.

After the white flash, the entire sky glowed green over the mid-Pacific for an instant, and a bright red glow formed around "sky zero" where the detonation had occurred. The initial fireball lasted less than a second before being dissipated along the Earth's magnetic field lines. This was followed by a bright red-orange auroral display lasting more than 7 minutes. Long-range radio communication was disrupted for a period of time ranging from a few minutes to several hours after the detonation (depending upon the frequency and the radio path being used).

In a phenomenon unrelated to the EMP, the radiation cloud from the Starfish Prime test subsequently destroyed at least 5 United States satellites and one Soviet satellite. The most well-known of the satellites was Telstar I, the world's first active communications satellite. Telstar I was launched the day after the Starfish Prime test, and it did make a dramatic demonstration of the value of active communication satellites with live trans-Atlantic television broadcasts before it orbited through radiation produced by Starfish Prime (and other subsequent nuclear tests in space). Telstar I was damaged by the radiation cloud. The damage to Telstar 1 increased each time that it traveled through the belt of radiation, and it failed completely a few months later.

(For more information on this satellite problem, see the first 31 pages of Collateral Damage to Satellites from an EMP Attack, which gives a considerable amount of information about this additional problem of nuclear EMP attacks. You can also obtain the lengthy complete report from the DTIC government site. That 2010 report was originally written in support of the United States EMP Commission.)

Nuclear EMP is actually an electromagnetic multi-pulse. The EMP is usually described in terms of 3 components. The E1 pulse is a very fast pulse that can induce very high voltages in equipment and along electrical wiring and cables. E1 is the component that destroys computers and communications equipment and is too fast for ordinary lightning protectors (although devices that are fast enough are routinely being produced, but are rarely used in the civilian infrastructure). The E2 component of the pulse is the easiest to protect against, and has similarities in strength and timing to the electrical pulses produced by lightning.

The E3 pulse is very different from the E1 and E2 pulses from an EMP. The E3 component of the pulse is a very slow pulse, so slow that most people would not use the word "pulse" to describe it. The E3 component lasts tens to hundreds of seconds, and is caused by the nuclear detonation heaving the Earth's magnetic field out of the way, followed by the restoration of the magnetic field to its natural place. The E3 component has similarities to a geomagnetic storm caused by a very severe solar storm.

In writings on the Internet, there is nearly always much confusion about the very different aspects of the various components of nuclear EMP. In addition, there is much confusion in distinguishing high-altitude nuclear EMP, non-nuclear EMP weapons and solar geomagnetic storms. There are very large differences among these very different electromagnetic disturbances; although there are many similarities linking solar-caused geomagnetic storms and the E3 component (but not the other components) of high-altitude nuclear EMP. Nearly everything written in popular articles, even in the most respectable publications, jumbles up a nearly incomprehensible mix of information confusing the effects of the E1 and E3 components of electromagnetic pulse. This has been largely responsible for the large number of widely-believed EMP Myths.

It is important to note that nuclear EMP cannot be understood without an understanding of the differences between the E1 and E3 components of nuclear EMP. Many intelligent technologists have caused an enormous amount of confusion by making statements without any clear understanding of the vastly different components generated by nuclear EMP. For a more detailed discussion of these components, see the E1-E2-E3 Page.

See the EMP Sitemap Page of the many EMP pages on this web site.

The E1 component of the pulse is the most commonly-discussed component. The gamma rays from a nuclear detonation in space can travel great distances. When these gamma rays hit the upper atmosphere, they knock out electrons in the atoms in the upper atmosphere, which (if they were not deflected by the Earth's magnetic field), would travel in a generally downward direction at relativistic speeds. This forms what is essentially an extremely large coherent vertical burst of electrical current in the upper atmosphere over the entire affected area. This current interacts with the Earth's magnetic field, causing the relativistic electrons to spiral around the magnetic field lines, producing a strong electromagnetic pulse, which originates a few miles overhead, even though the nuclear detonation point may be a thousand miles away or more. Since the E1 pulse is generated locally, even though the original gamma ray energy source may be in space at a great distance away, the pulse can cover extremely large areas, and with an extremely large EMP field over the entire affected area.

Illustration above is from the United States Defense Threat Reduction Agency about the E1 component of nuclear electromagnetic pulse. The source region is the region of the upper atmosphere where gamma radiation from the weapon knocks out electrons from atoms in the atmosphere, which travel in a generally downward direction at roughly 94 percent of the speed of light, and are acted upon by the Earth's magnetic field to generate a powerful burst of electromagnetic energy. This source region, where the EMP is actually generated, is a very large area in the middle of the stratosphere. (In the map on the right side of the illustration, HOB is the height of the nuclear burst in kilometers.)

The magnitude of a nuclear EMP over the United States would be much larger than the tests in the Pacific would indicate. For any particular weapon, the magnitude of the all of the components of an EMP are roughly proportional to the strength of the Earth's magnetic field. The Earth's magnetic field over the center of the continental United States is about twice the strength as at the location of the Starfish Prime test.

See the separate article on the high-altitude nuclear tests of Operation Fishbowl.

It is important to emphasize that, although EMP attacks affecting all of the continental United States are possible, smaller regional EMP attacks, launched to lower altitudes with a smaller missile or with a high-altitude balloon are probably much more likely. These lower altitude attacks would affect a much smaller area, and would probably be of a much smaller intensity, but could still be very damaging to data centers and other facilities with a high reliance upon microelectronics.

Starfish Prime was a 1.44 megaton thermonuclear weapon, but was actually extremely inefficient at producing EMP. Much smaller nuclear fission weapons, requiring far less expertise, would be much more efficient at producing EMP, especially the very fast E1 component. In general, the simpler the nuclear weapon, the more efficient it is at producing EMP. (See the the notes on EMP page.) Thermonuclear weapons (so-called hydrogen bombs) are usually very inefficient at generating the fast-rise-time E1 pulse. (Weapons with a high energy yield are much better at generating the slower geomagnetic-storm-like E3 pulse that caused much of the damage to Kazakhstan in the Soviet test mentioned below. This E3 pulse can induce large currents even in long underground lines.)

Several countries have produced single-stage nuclear weapons with energy yields of well over 100 kilotons. These would be much more efficient at producing EMP than the Starfish Prime detonation. (The very first nuclear weapon tested by France had a yield of 70 kilotons). In the early 1950s, the United States had a stockpile of 90 bombs of a high-yield fission weapon that would have been a powerful EMP weapon. These were 500-kiloton single-stage fission bombs known as the Mark 18. Very little was known about EMP at the time that the Mark 18 was in production. The only actual test of the Mark 18 bomb was done at the Pacific Ocean test range on November 16, 1952 at an altitude of only 1480 feet (450 meters), so nothing was discovered about its possibilities for high-altitude EMP (although it appears that the actual yield was closer to 540 kilotons, which was higher than its design yield). By now, some countries undoubtedly have very advanced enhanced-EMP nuclear weapons, although these details are highly classified.

The Mark 18 bomb, tested in 1952, was also known as the super oralloy bomb. It was made of a spherical shell of very highly-enriched uranium surrounded by a sophisticated symmetrical implosion system that was 44 centimeters in thickness. Although it is often described as a very advanced device, it was designed by people who did not have computers of a power that is anything even approaching the power of computer that you are using to read this web page. More than a half-century ago, at least 90 of these bombs were built by the United States. In 1952, they were trying to conserve the highly-enriched uranium in the stockpile, so the Mark 18 was surrounded with a natural uranium tamper. Anyone making a similar weapon for EMP use could probably enhance its EMP effects by using a tamper made of enriched uranium and using a relatively thin outer casing made of a relatively gamma-ray-transparent high-strength alloy. In addition, there are techniques for increasing the energy of the gamma rays beyond the levels available in first and second generation nuclear weapons. These techniques would increase the electric field of the EMP at least somewhat beyond the old maximum of 50,000 volts per meter, although we don't know by how much.

Today, if just one of these 500 kiloton bombs like the Mark 18 were detonated 300 miles above the central United States, the economy of the country would be essentially destroyed instantaneously. Very little of the country's electrical or electronic infrastructure would still be functional. This is not to say that every device would be destroyed, but the interdependence of different electrical and electronic infrastructures makes it possible to stop nearly all economic activity with only limited damage to critical infrastructures. It would likely be months or years before most of the electrical grid could be repaired because of the destruction of large numbers of transformers in the electric power grid. Several countries today have the ability to produce a weapon similar to this 1952 bomb, and send it to the necessary altitude. (England tested a single-stage weapon with a yield of 720 kilotons, called Orange Herald, on May 31, 1957.) The number of countries with this ability will undoubtedly be increasing in the coming years.

For an explanation of why the all of the nuclear weapons so far tested above ground have been suppressed-EMP weapons, and the ease with which those weapons could have been made into enhanced-EMP weapons, see the first half of the web page on Super-EMP Weapons.

The instantaneous shutdown of the power grid would occur primarily because of the widespread use of solid-state SCADAs (supervisory control and data acquisition devices) in the power grid. These would be destroyed by the E1 pulse, but could probably be replaced within a few weeks. The greater problem would be in re-starting the power grid. (No procedures have ever been developed for a "black start" of the entire power grid. Starting a large power generating station actually requires electricity.) The greatest problem would be the loss of many critical large power transformers due to geomagnetically induced currents, for which no replacements could be obtained for at least a few years. The loss of many of these power transformers would greatly complicate the re-start of the parts of the grid that could be much more quickly repaired. The loss of a sufficient number of these large power transformers would effectively destroy the power grid as we now know it. We would have to just hope that there were enough small islands of local electric power to enable a basic subsistence level of economy to exist.

The consequences of the potential dangers to the electric power grid have changed dramatically over the past few decades -- as the availability of electricity has changed from being a convenience to something upon which our lives now depend. This transition of electricity from a convenience to a necessity for sustaining human life has happened so gradually that most of us haven't noticed this profound change. The knowledge and the technology of earlier times for surviving for long periods of time without electricity has been mostly lost in modern societies.

By mentioning the 1952 Mark 18 bomb, I do not want to imply that countries developing nuclear weapons would start with such an old technology. New 21st century automobile companies do not start with a Stanley Steamer or the Model T; and new radio companies do not start with Marconi circuits and Fleming valves. Modern techniques and materials, as well as advanced computing power, enable new nuclear weapons projects to leapfrog far past the Manhattan Project. A related fallacy is the belief that, because of the difficulty that the United States and the old Soviet Union had in going from basic fission weapons to thermonuclear weapons, all nations would experience similar difficulties and delays. Producing basic fission weapons requires a significant industrial capacity to produce the fissionable material. Scaling up from there to thermonuclear weapons just requires computing power and knowledge.

Many years after he left the nuclear weapons laboratories, the principal designer of the Mark 18 bomb wrote an article for Scientific American describing, in general terms, how specific effects of nuclear weapons (including EMP) can be greatly enhanced, and how such effects can be concentrated in one direction from the detonation. (See Scientific American, Theodore B. Taylor "Third-Generation Nuclear Weapons", pages 30-39. Vol. 256, No. 4. April, 1987.)

The Soviet Union got its introduction to the severity of high-altitude nuclear EMP effects over a much more heavily populated area than the Pacific Ocean. The most damaging nuclear EMP event in history (so far), much worse than the Starfish Prime test, occurred in October of 1962 over central Asia. Written documents give the time and date as 3:41 GMT/UTC on the morning of October 22, 1962. The warhead was launched from Kapustin Yar on a Soviet R-12 missile. Although the primary purpose of the test was to discover the effects of EMP on certain military systems, the large magnitude of some of the effects on the civilian infrastructure were quite unexpected.

A few hours after the sun rose in Kazakhstan on that cloudy October morning, the Soviet Union detonated a 300 kiloton thermonuclear warhead in space at an altitude of 290 kilometers (about 180 miles) over a point just west of the city of Zhezkazgan in central Kazakhstan. The test was generally known only as Test 184 (although some Soviet documents refer to it as K-3). It knocked out a major 1000-kilometer (600-mile) underground power line running from Astana (then called Aqmola), the capital city of Kazakhstan, to the city of Almaty. Some fires were reported. In the city of Karaganda, the EMP started a fire in the city's electrical power plant, which was connected to the long underground power line.

The EMP also knocked out a major 570 kilometer long overhead telephone line by inducing currents of 1500 to 3400 amperes in the line. (The line was separated into several sub-lines connected by repeater stations.) There were numerous gas-filled overvoltage protectors and fuses along the telephone line. All of the overvoltage protectors fired, and all of the fuses on the line were blown. The EMP damaged radios at 600 kilometers (360 miles) from the test and knocked out a radar 1000 kilometers (600 miles) from the detonation. Some military diesel generators were also damaged. The repeated damage to diesel generators from the E1 component of the pulse after the series high-altitude tests was the most surprising aspect of the damage for the Soviet scientists.

Subsequent analysis has shown that the warhead used in the 1962 Soviet test was particularly ineffective at generating EMP. If the W49 warhead used in the U.S. Starfish Prime test had been used in the Soviet tests, the EMP damage over Kazakhstan would have been far greater. If the weapon used in the earlier U.S. 3.8 megaton Hardtack-Teak high altitude test had been used, the damage would have been greater still.

Both the United States and the Soviet Union detonated EMP-generating nuclear weapons tests in space during the darkest days of the Cuban Missile Crisis, when the world was already on the brink of nuclear war.

The Soviet Union detonated additional 300 kiloton weapons over Kazakhstan on October 28 and November 1, 1962. The United States detonated a relatively small nuclear weapon (probably about 7 kilotons) in space over the Pacific on October 20, 1962, and also detonated 400 kiloton nuclear weapons in space over the Pacific on October 26 and November 1, 1962. (During the period of October 13 to November 1, 1962 there were 16 Soviet and 6 United States above-ground nuclear explosions.) Two people suffered retinal burns when they looked toward the nighttime flash of the October 26 (Bluegill Triple Prime) detonation directly overhead, which occurred at an altitude of 50 kilometers. (Due to a guidance system malfunction, the October 26 detonation occurred almost directly above Johnston Island.)

Johnston Island is now somewhat larger than it was in 1962 (due to a dredging project in 1964), and the airport is now closed. There have been at least three launch pad sites on Johnston Island for high-altitude nuclear tests. The 1958 tests (Hardtack-Teak and Hardtack-Orange) were launched from one end of the island, and the Operation Fishbowl tests, including Starfish Prime, were launched from the other end. After the Bluegill Prime launch resulted in a catastrophic explosion shortly after the successful Starfish Prime test, the destroyed launch pad was re-built, along with a spare launch pad. You can see the current island in this Wikimapia satellite view of Johnston Island.

Most of the EMP data on the United States Bluegill Triple Prime, Checkmate and Kingfish high altitude tests of 1962, as well as the Hardtack-Teak and Hardtack-Orange tests of 1958 remain classified decades after the tests were completed. The secrecy regarding these tests poses a danger to the United States since it does not allow vulnerable United States citizens to fully educate themselves about the effects of weapons that could have a dramatic effect on their lives in the future. It is likely, however, that data on the E1 resulting from the Hardtack-Teak and Hardtack-Orange tests were never obtained due to poor understanding in 1958 of the high-altitude EMP phenomenon. The Teak and Orange tests were detonated at a much lower altitude than Starfish Prime. The Teak and Orange warheads would have caused much more damage in Hawaii than Starfish Prime if they had been detonated at the same altitude. The Teak and Orange warheads were more than twice as powerful, and they also produce more than 5 times as much prompt gamma radiation as Starfish Prime. The higher prompt gamma output would have had especially severe consequences for the EMP at a distant location like Hawaii.

Test 184 was launched from Russian territory about 30 miles from the Kazakhstan border. If Test 184 were to be duplicated today using the same launch and detonation points, it would probably be considered as a nuclear attack against another country. (At the time, of course, Kazakhstan was a part of the Soviet Union.)

There is a separate page with more details, including references, about the Soviet nuclear EMP tests in 1962.

In the final analysis, however, all of those nuclear weapons detonated before 1963 were suppressed-EMP nuclear weapons. A few simple modifications would make an enhanced EMP nuclear weapon that is lighter, smaller, and in some respects, simpler to make.

This site is written by an electronics engineer who has been concerned about the possibility of an EMP attack on the United States for decades. We are entering a period of special vulnerability to EMP in the coming years as industrial civilization is now almost totally dependent upon microelectronics. (Hopefully, the use of fiber optics will reduce the current vulnerability within the next ten years, and possibly SCADAs will be better protected. Also, something desperately needs to be done about the electric power grid transformer situation.)

Most people who have some knowledge in this subject, and who have given some serious thought to the problem, consider the probability of an EMP attack on the United States during the next ten years at somewhere between 20 and 70 percent. The probability of a solar storm large enough to destroy hundreds of the largest transformers in the United States power grid sometime during this century is widely considered to be in the range of 50 to 90 percent.

(My own guess is that the probability of a long-term loss of much of the world's power grid from a solar superstorm is probably much larger than the chance of a nuclear EMP attack on the United States; however the extreme vulnerability of the United States critical infrastructure simply invites a nuclear EMP attack.)

The time that it would take to recover from a nuclear EMP attack has generally been estimated to be anywhere from two months to ten years. There would almost certainly be a time of great economic hardship. Whether this time of economic hardship is of short or long duration will depend upon the reaction of the American people after the event, and whether any preparation has been made in advance of the event. So far, such advance preparation has been almost totally absent.

In widespread power outages of the past in the United States, people have reacted with behavior ranging from rioting and looting (as many did during the July 13, 1977 New York power outage) to patiently waiting for the crisis to be over (as has occurred with some more recent power outages such as the widespread August 14, 2003 outage in the northeastern U.S.).

If the recovery period were long, and especially if electronic communication were down for a period of months, civilization in the United States could reach a tipping point where recovery would become difficult or impossible.

The electric power grid in use today has changed very little from the system devised by Nikola Tesla and implemented by Westinghouse, beginning in the 1890s. The adaption of alternating current made modern electrification possible, but also made the power grid very vulnerable to geomagnetically induced currents, which includes the currents induced by the E3 component of nuclear EMP, as well as severe solar storms.

Lots more:

http://www.futurescience.com/emp.html