America's Vulnerability to a Different Nuclear Threat: AnElectromagnetic Pulse

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America's Vulnerability to a Different Nuclear Threat: AnElectromagnetic Pulse

May 26, 2000 20 min read
Jack Spencer
Senior Research Fellow for Energy and Environmental Policy
Jack Spencer is a Senior Research Fellow for Energy and Environmental Policy at The Heritage Foundation.

In the 1980s, Americans feared neutron bombs that could kill everyone but leave buildings, roads, and cars intact. Today, Americans should fear a different kind of nuclear threat that can instantaneously destroy power grids, electronic systems, and communications along an entire coast but spare people.

This destruction would result from the split-second release of a high-energy electromagnetic pulse (EMP) after a nuclear bomb is detonated miles above the Earth and outside the atmosphere. Within a week of the blast, although no one would be instantly killed, the disruption of food and water supplies and health care caused by the shutdown of transportation, computers, networks, electronic equipment, and communication systems would have serious consequences for millions of people.2 Recovering from such an attack could take years.

The U.S. military first witnessed this phenomenon after a series of high-altitude nuclear tests in the Johnston Atoll in 1962 generated a disruption in electronic equipment in Hawaii, nearly 1,000 miles away. According to reports, the EMP interrupted radio broadcasts, caused streetlights to malfunction and burglar alarms to sound, and resulted in electronic failures across the islands despite their great distance from the test site.3

Little has been done to protect electrical systems from this threat beyond the nation's nuclear war-fighting infrastructure. The reason: During the Cold War, only the Soviet Union had the ability to mount an EMP attack against the United States, and if it had launched such an attack, the result would have been nuclear war. It made no sense to spend money to protect civil infrastructure from an electromagnetic pulse since little would be left standing after a nuclear bomb landed on U.S. soil.

Today, because of the spread of nuclear technology and ballistic missiles, the threat of a high-altitude EMP explosion over the United States or a battlefield is increasing. Indeed, America's reliance on advanced electronics makes its systems more vulnerable to such a blast than those of hostile states that might choose to use an EMP. Moreover, protecting all of America's civilian electronic infrastructure is fiscally not feasible. Because the most likely vehicles for delivering such a nuclear device above the atmosphere are ballistic missiles, the most prudent method of protecting America from EMP attacks would be a missile defense system that could destroy a ballistic missile before it reaches U.S. airspace.

Under what circumstances would an EMP attack on the United States be likely to occur? The possible scenarios range from one involving a rogue state's desire to demonstrate its potential ability to strike U.S. territory with a nuclear bomb to one in which such a state wants to give itself an advantage in a regional conflict by crippling U.S. military and allied forces, which are more dependent on advanced electronics and therefore more susceptible to an EMP attack.

Congress is well aware of the increasing threat. The Senate will have an opportunity to address the vulnerability of military and civilian systems to such an attack when it considers the fiscal year (FY) 2001 defense authorization bill (H.R. 4205) passed by the House on May 18. Representative Roscoe Barlett (R-MD) authored a provision of this bill (Title XIV) to establish a Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack. This would be an important first step.

In addition, Congress should hold hearings to establish what missile defense system could intercept ballistic missiles armed with nuclear warheads that could be detonated above the atmosphere, and it should continue to press the Administration to proceed quickly toward the deployment of an effective national missile defense system.


The scientific principles behind generating a high-altitude electromagnetic pulse are relatively easy to understand. A nuclear weapon is detonated between 25 miles and 300 miles above the Earth's surface; the radiation reaching the atmosphere interacts with air molecules to produce high-energy electrons that speed across the Earth's magnetic field as an instantaneous, invisible electromagnetic pulse.4 A nuclear device must be detonated above the Earth's atmosphere in order to generate the high-altitude EMP effects.

An EMP can have devastating consequences for developed countries, because any metallic conductor in the area affected becomes a "receiver" for the powerful energy burst released by the blast. Such receivers include anything with electronic wiring--from airplanes and automobiles to computers, railroad tracks, and communication lines. If systems connected to these receivers are not protected, they will be damaged by the intense energy pulse. Indeed, depending on the strength of the pulse and the vulnerability of the equipment, the effects could range from interrupted phone conversations and radio interference to the melting of components in every type of electrical system.

An EMP damages unprotected electronic equipment within the blast's "line of sight." The size of the area in harm's way (the EMP's "footprint" on the Earth's surface) is determined by the altitude of the explosion. The higher the altitude, the greater the land area affected (see Map 1). A Scud-type ballistic missile launched from a vessel off the U.S. coast and detonated at an altitude of 95 miles would degrade electronic systems across one-fourth of the United States. A Taepo Dong-2 missile launched from North Korea probably could deliver a warhead 300 miles above America--enough to degrade electronic systems throughout the country. Crude weapons with low yields, like those used against Japan in World War II, would have ample power to cripple the United States.

Possible EMP Scenarios

Although the threat that an enemy would use a high-altitude EMP against America existed during the Cold War, the likelihood that this could happen may be greater today.5 During the Cold War, an EMP attack was viewed as the first step in launching a nuclear war, but it was never tried because the threat of massive nuclear retaliation provided an effective deterrent. This principle holds true today for an attack by Russia or China on the United States.

In the post-Cold War years, the proliferation of weapons of mass destruction makes the threat more difficult to assess. More important, the traditional deterrent of retaliation does not apply. No rogue nation has the capacity to fight a general nuclear war with the United States; therefore, it is not likely that an EMP blast would be used as a precursor to full-scale war. And since an EMP blast is not likely to kill anyone directly or to be followed by a nuclear strike that would annihilate U.S. cities, the United States is less likely to retaliate and destroy an entire nation of innocent people as punishment for the decisions of a rogue leader. The motivation for a rogue state to use its limited nuclear arsenal in an EMP strike against the United States is simple: It maximizes the impact of its few warheads while minimizing the risk of retaliation.

This decrease in risk for rogue leaders could compel them to use EMP to offset overwhelming U.S. conventional power on the battlefield. An EMP blast would debilitate U.S. forces in a hot spot where they might be deployed and throughout a region of strategic interest, such as Northeast Asia or the Middle East. Because the United States has no policy on deterrence for a rogue state's use of high-altitude EMP, and because EMP attacks are less risky for those states, such attacks are far more likely to occur in this era of nuclear proliferation than they were at any time during the Cold War.

The national missile defense architecture planned by the Administration, with 100 ground-based interceptors stationed at one site in Alaska, may be unable to intercept a nuclear warhead before it detonates above U.S. territory, and it would have virtually no chance of intercepting such a missile above a theater of combat.

Consider these possible scenarios.

Scenario #1: A rogue-state leader decides to launch an EMP attack on the United States to improve the odds of winning a regional conflict. After obtaining an ICBM equipped with a nuclear warhead, Saddam Hussein decides to invade Kuwait again.6 The United States is called upon to liberate its ally. A few weeks into the war, Saddam launches a ballistic missile armed with a nuclear warhead toward the United States. It is detonated 50 miles above a section of the American West. Although no people are harmed, there is a regional blackout. Saddam Hussein gloats, having leveled the playing field and weakened U.S. resolve by demonstrating his ability to deliver a nuclear weapon to U.S. soil. The President refuses to launch a counter nuclear attack out of fear that it would kill millions of innocent people.

Scenario #2: An enemy explodes a nuclear device over a theater of combat or an area containing allied assets to cripple the United States. North Korea has decided to take South Korea but faces 37,000 U.S. troops stationed there. It explodes a nuclear device over the extreme southern part of the Korean peninsula. The EMP effect covers all of Korea, with the strongest effects occurring below the demilitarized zone. North Korea's military is harmed, but the damage is far less severe than that experienced by U.S. and South Korean forces since they rely on modern electronics to a much greater extent. Because the U.S. and allied forces are unable to utilize their advanced radar, communications, and networked systems, they suffer a major decline in warfighting capabilities. Electronic systems on a carrier battlegroup on its way to the Korean theater are damaged as well. As a result, the United States is seriously constrained in responding to a North Korea attack across the demilitarized zone.

Scenario #3: A surprise terrorist attack is launched against the United States, but the aggressor cannot be identified. An unknown aggressor launches a ballistic missile with a nuclear warhead from a ship located at sea 150 miles east of New York City. The device explodes 80 miles above New York, spreading its effect over most of New York and Pennsylvania. Wall Street shuts down, massive traffic tie-ups occur throughout the metropolitan region, and air traffic control systems are severely degraded. The crew of the ship immediately abandons the vessel and sinks it, and no one admits responsibility. Analysis leads the U.S. government to believe that the missile was probably a Scud variant, but because the United States cannot identify who launched it, there is no basis for retaliation.

Scenario #4: An enemy uses an EMP blast as part of its war strategy against a U.S. ally. Suppose China commences another military exercise in the Taiwan Strait. As part of the exercise, it launches a ballistic missile in a trajectory over Taiwan. When the missile reaches 300 miles southeast of Taiwan, its nuclear warhead is detonated, releasing an EMP that affects the entire island. The ensuing blackout incites mass confusion and seriously degrades the warfighting ability of the Taiwanese military. Taiwan is unable to defend itself and is forced either to sue for peace with the mainland or to call in the United States to defend it from attack.

Scenario #5: A rogue leader wants to attack the United States but evade retaliation. Iran, which the 1998 Commission to Assess the Ballistic Missile Threat to the United States (the Rumsfeld Commission) reported "has the technical capability and resources to demonstrate an ICBM-range ballistic missile...within five years of the decision to deploy," decides to take hostile action against the United States after developing an ICBM.7 It knows that a direct nuclear attack on the United States would result in the destruction of Tehran.8 It launches two missiles with nuclear warheads that detonate 250 miles above Illinois and Wyoming. The United States does not retaliate because no one is immediately killed. Not knowing whether Iran has other nuclear warheads, the United States decides to limit its response against Iran rather than risk a direct nuclear attack on a U.S. city.


Scientists studied the effects of an electromagnetic pulse from a high-altitude nuclear blast in depth during the Cold War. Models of how U.S. and Soviet military systems were likely to respond were developed. Significant investments were made to protect, or "harden," America's strategic nuclear forces and its associated command and control systems against the harmful effects of EMP blasts. But many systems that were not deemed vital during a nuclear war, such as non-strategic command and control, were left unprotected. Under the strategic circumstances of the Cold War between the Soviet Union and the United States, all that was necessary was to ensure the survivability of nuclear forces because very little could survive on the ground should a nuclear war erupt.

The need to harden more systems is becoming more of an issue in light of the proliferation of nuclear know-how and ballistic missile technology to Third World countries--a serious threat that was made even clearer by the report of the congressionally mandated Rumsfeld Commission. Since the release of an unclassified summary of the commission's report in mid-1998, various U.S. Department of Defense officials have testified before Congress on the seriousness of an EMP attack. For example, Colonel Richard Skinner, the principal director of the Department of Defense's Command, Control, Communications, Intelligence, Surveillance, and Reconnaissance Unit and Space Systems, stated that "While an unlikely threat, EMP...weapons would have serious impact to military command and control systems."9

The commercial mass production of advanced electronic systems has made high-quality electronic devices exceedingly affordable, and slashed defense budgets force the U.S. military to look for cost savings wherever possible. Thus, the military increasingly has been purchasing commercial products for use in U.S. weapons systems. The new, advanced tactical Tomahawk cruise missile, for example, will use commercial electronics.10 This disturbing fact is highlighted by the comments of the deputy chief of the Joint Chiefs of Staff's Command Center, Stanley Jakubiak: "[T]he military has...taken a simplistic approach. We've...assumed that all commercial equipment would fail under an EMP pulse."11 Not only are many military systems vulnerable, but so are the systems that Americans rely on every day.

On July 15, 1996, President Bill Clinton issued Executive Order No. 13010, in which he identified eight infrastructure systems critical to the nation's survival: telecommunications, electric power systems, oil and gas storage, transportation, banking and finance, storage and transportation, water supply systems, and emergency services (including medical, police, fire and rescue, and continuity of government). Retired Air Force General Robert T. Marsh, chairman of the President's Commission on Critical Infrastructure Protection, has testified to the House National Security Committee that "the nuclear threat from hostile nations can not be dismissed today," and "a high altitude EMP attack could devastate the telecommunications and other critical infrastructure." 12 Although he conceded that the systems were vulnerable, he admitted that the Administration was "not considering any special measures to counter such a threat."13

Not everyone agrees about the effects of a high-altitude EMP for civil infrastructure. A 1991 study on the "Effects of Geomagnetic Disturbances on Electric Power Transmission Systems" published by the Electrical Power Research Institute, for example, points out that natural phenomena such as solar storms may cause more damage than an EMP blast.14 But according to Dr. Gordon Soper, a former Defense Department official responsible for nuclear, chemical, and biological defense programs who testified before the House Small Business Committee, "an EMP attack would result in an unacceptable disruption and damage to our commercial electronic infrastructure."15 Almost without exception, experts agree that a high-altitude EMP would damage America's electronics. They disagree about the extent of the damage and what should be done to prevent it.

Regardless of the debate, the surest way to protect the United States from a high-altitude EMP is to deploy a ballistic missile defense that would give the United States an opportunity to intercept and destroy a warhead before it is detonated above the atmosphere. This would prevent an EMP attack and any harm to U.S. systems, and it might even deter rogue leaders from considering the use of EMP. Deploying a missile defense architecture that is capable of intercepting a missile early in flight (during the ascent phase) means that rogue-state missiles would be ineffective, thereby undermining the rationale for their use.

Protecting Against High-Altitude EMPs. There are methods to test system vulnerability to EMPs without exploding nuclear weapons. For example, a system could be injected with current and voltage to see how it would react. The United States has several simulators that could be modified to emulate the EMP effect of a high-altitude nuclear blast. The Defense Special Weapons Agency and its predecessors have already developed models that closely reproduce the effects of the high-altitude tests over the Pacific, which were validated by underground nuclear testing.

To protect electronics, an entire system must be encased in a metallic shield that prevents any external electromagnetic pulse from entering. Moreover, antennas and power connections must be equipped with surge protectors, windows must be coated with wire mesh or conductive coating, and doors must be sealed with conductive gaskets. Fiber optic cable is not vulnerable to EMP, but the switches and controls that use microelectronics in conjunction with the fiber optic cable are, and should be protected. Continuing efforts to replace copper communications cable with fiber optic cable will reduce overall EMP vulnerability significantly. And to ensure that protection lasts over the lifetime of the equipment, maintenance and testing should be performed on a system regularly. If a system is modified, fixed, or serviced, its EMP vulnerability should be assessed.

All of these steps can be affordable. Assuming these protections are engineered into a product or building from the outset would add as little as 1 percent to 5 percent to overall costs. (Retrofitting systems, however, could add substantial costs.) EMP surge protectors have become very inexpensive. According to George Ullrich, Deputy Director of the Defense Special Weapons Agency, such hardening is needed: "systems, such as commercial power grids [and] telecommunications networks...remain vulnerable to widespread outages and upsets due to high altitude EMP. While DOD hardens assets it deems vital, no comparable civil program exists."16

Because these steps have not been taken, there is little doubt among the experts that high-altitude EMPs will harm the systems that Americans and their armed forces rely on each day. Now the debate is over the extent of the vulnerability, the probability that it will occur, how to reduce the vulnerability, and how to respond to an attack.


To begin developing a policy for protecting Americans from the effects of a high-altitude EMP blast, Congress should:

  • Hold hearings on whether the Administration's planned national missile defense architecture can protect the United States, its allies, and its troops stationed abroad from an EMP delivered by ballistic missiles and examine national missile defense alternatives to that system to ensure that America deploys the best protection technologically possible.

  • Continue pressing the Administration to deploy a national missile defense system as soon as technologically possible. As numerous officials and the Heritage Foundation Commission on Missile Defense chaired by Ambassador Henry Cooper have stated, the best defense involves a system that includes sea-based, space-based, and land-based interceptors that can respond to any ballistic missile launch to intercept the missile as near its boost phase as possible.

  • Establish a blue-ribbon commission to (1) assess the immediacy of the EMP threat to America and the level of civil and military vulnerability, (2) recommend a level of just force in retaliation for EMP attacks, (3) conduct a cost-benefit analysis for protecting civil and unhardened military electronic infrastructure against EMPs, and (4) determine the extent to which America's potential enemies have access to this technology and the ease with which they could use it.


On July 15, 1998, the bipartisan Commission to Assess the Ballistic Missile Threat to the United States, chaired by former Secretary of Defense Donald Rumsfeld, released an unclassified summary of its report to Congress. The report stated that nations with established short-range ballistic missiles could develop an ICBM "within about five years of a decision to acquire such a capability."17 This dispelled the myth--supported by the Administration--that a threat to the United States from Third World ballistic missiles would not arise for at least 10 to 15 years.

As if to confirm the Rumsfeld Commission's assessment, within two months of the report's release, North Korea tested a prototype ICBM. Because the United States cannot defend itself from even one ballistic missile, Congress reacted immediately to make it the policy of the United States to deploy a national missile defense system as soon as technologically possible.

This is even more important in light of the possible threat of high-altitude EMP blasts. All of the warning signs are present. The United States is increasingly reliant on vulnerable advanced electronics, and the weapons and missiles needed to mount an EMP assault are proliferating at a dangerous pace. Yet the U.S. military lacks a coherent policy on how to respond to an attack. America needs an authoritative voice--a blue-ribbon commission modeled after the Rumsfeld Commission--that can define the problem in realistic terms for Congress and recommend the steps to take to mount an adequate defense against the EMP threat.

Jack Spencer is Policy Analyst for Defense and National Security in the Kathryn and Shelby Cullom Davis Institute for International Studies at The Heritage Foundation.



1. For more on high-altitude EMPs, see "U.S. Representative Roscoe Bartlett (R-MD) Holds Hearing on Electromagnetic Pulse and Business," House Small Business Committee Subcommittee on Government Programs and Oversight, FDCH Political Transcripts, Federal Document Clearing House, Inc., June 1, 1999; "U.S. Representative Curt Weldon (R-PA) Holds Hearing on Effect of Electromagnetic Pulse Attacks," House Armed Services Committee Subcommittee on Military Research and Development, FDCH Political Transcripts, October 7, 1999; "Hearing of the Military Research and Development Subcommittee of the House National Security Committee on Electromagnetic Pulse Threats," Federal News Service, Federal Information Systems Corporation, July 16, 1997; and Office of Technology Assessment, "The Effects of Nuclear War," May 1979.

2. Philip J. Klass, "Study Raises Doubt on EMP Protection," Aviation Week & Space Technology, September 17, 1984, p. 76.

3. Bill Prochnau, "Doomsday Fears, Once Submerged, Rise to a Renewed Crest," The Washington Post, April 26, 1982, p. A1.

4. For a scientific description of the physics of high-altitude electromagnetic pulses, see Gary Smith, testimony "Electromagnetic Pulse Threats" before the Subcommittee on Military Research and Development, Committee on National Security, U.S. House of Representatives, July 16, 1997.

5. For an analysis of the fear concerning an EMP attack during the Cold War, see David Burnham, "U.S. Fears One Bomb Could Cripple the Nation," The New York Times, June 28, 1983, p. 1.

6. Pamela Hess, "Iraq Close to Nuclear Bomb," UPI News Article, March 22, 2000, at  (March 23, 2000).

7. "Executive Summary," Report of the Commission to Assess the Ballistic Missile Threat to the United States, published pursuant to Public Law 201, 104th Cong., July 15, 1998, p. 12-13.

8. James Risen and Judith Miller, "C.I.A. Tells Clinton an Iranian A-Bomb Can't Be Ruled Out," The New York Times, January 17, 2000, p. 1.

9. "U.S. Representative Roscoe Bartlett (R-MD) Holds Hearing on Electromagnetic Pulse and Business."

10. Robert Holzer, "Tomahawk Schedule Should Survive Rise in Cost," Defense News, May 15, 2000, p. 8.

11. "U.S. Representative Curt Weldon (R-PA) Holds Hearing on Effect of Electromagnetic Pulse Attacks."

12. General Robert T. Marsh, USAF (Ret.), testimony, "Hearing of the Military Research and Development Subcommittee of the House National Security Committee on Electromagnetic Pulse Threats," July 16, 1997.

13. Ibid.

14. An abstract of this report may be found at the Electrical Power Research Institute Web site,

15. "U.S. Representative Roscoe Bartlett (R-MD) Holds Hearing on Electromagnetic Pulse and Business."

16. "Hearing of the Military Research and Development Subcommittee of the House National Security Committee on
Electromagnetic Pulse Threats," July 16, 1997.

17. "Executive Summary," Report of the Commission to Assess the Ballistic Missile Threat to the United States, p. 5.


Jack Spencer
Jack Spencer

Senior Research Fellow for Energy and Environmental Policy

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