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EMP as a Potential Terrorist Weapon

Congressional Research Report

By: Clay Wilson

Date: August 20, 2004

Source: Excerpt from "High Altitude Electromagnetic Pulse (HEMP) and High Power Microwave (HPM) Devices: Threat Assessments." Congressional Research Service Report written for Congress by Clay Wilson, August 20, 2004.

About the Author: Clay Wilson is a specialist in the Technology and National Security Foreign Affairs, Defense, and Trade Division for the Congressional Research Service. The Congressional Research Service (CRS), part of the Library of Congress, prepares it's reports for the U.S. Congress.


An electromagnetic pulse (EMP) is capable of permanently disabling mechanical and electronic systems. As a potential weapon, the EMP was first recognized as an unintended consequence of nuclear explosions during the 1950s, when the United States and the Soviet Union were conducting atmospheric nuclear tests. During one such test in the Pacific Ocean, EMPs knocked out streetlights in Hawaii and disrupted electrical systems as far away as Australia.

By the beginning of the twenty-first century, American and British scientists had the technology to develop E-bombs capable of generating EMPs. Carbon-graphite coils that are capable of generating an electromagnetic pulse which destroys electronics equipment—especially communications equipment—can be fitted to existing missiles. Carbon-graphite equipped cruise missiles were used by U.S.-led forces in raids on Baghdad, Iraq in 1991 and in 2003.

At the same time, scientists and defense analysts warned that terrorists might be capable of building their own, much less sophisticated devices for a fraction of the cost to a superpower.

Following the terrorist attacks on the United States on September 11, 2001, lawmakers, policy planners, the military, the intelligence community, and the general public grew increasingly concerned about the nature and source of possible future terrorist threats, a fear compounded by the anthrax scare that began just weeks after September 11th. The government commission that investigated the attacks (the 9-11 Commission) concluded that in part they resulted from a failure of imagination on the part of the United States; that is, because no one imagined that terrorists could commandeer jetliners and fly them into buildings, no one took steps to prevent it from happening. In the years following the attacks, however, planners flexed their imagination, even to the point of hiring Hollywood scriptwriters as consultants to envision the form that future terrorist attacks might take.

One threat that received increasing attention is the "E-bomb," a bomb designed not to destroy targets or kill people, but rather to generate a powerful EMP that could knock out electronic circuitry, telecommunications systems, computers, satellites, electrical transformers, and anything that relies on or transmits electrical current. In 1925, American physicist and future Nobel laureate Arthur H. Compton (1892–1962) demonstrated that when a string of subatomic energy packets called photons were fired into atoms with a low atomic number—atoms with a relatively small number of protons in their nuclei—the atoms would eject electrons. This phenomenon, known as the Compton effect, is the principle underlying the E-bomb. If enough atoms eject enough electrons, which have a negative electric charge, the result is a massive electromagnetic pulse.

In a worst-case situation following a high energy EMP, hospitals would be unable to function, food supplies would rot, motorists would be unable to pump gas, lights and generators would not work—the resulting breakdown in social order could cause great damage to the nation and take years to repair.

Scientists concluded that a large nuclear explosion at very high altitude over the middle of the United States, or any other country, could instantly render the nation without vital communication links. In a 1985 report to the president, for example, the National Security Telecommunications Advisory Committee highlighted the vulnerability of the nation's telecommunications infrastructure to a high-altitude EMP blast—one that would, in this instance during the Cold War (1945–1991), presumably be launched by the Soviets as a preliminary step in an all-out nuclear attack.

In the new century, planners are worried less about an EMP attack from a nation-state than about the threat posed by terrorists who could get their hands on a device that could generate a large EMP and who would be willing to use it. More concerning is the fact that it is not even necessary to possess nuclear technology to generate a devastating EMP.

In 2001, the Commission to Assess the Threat from High Altitude Electromagnetic Pulse was established by Congress to study the vulnerabilities of critical U.S. infrastructure to EMP attack. In 2004, the U.S. Congress House Armed Services Committee subsequently conducted hearings to assess the threat to the United States from electromagnetic pulse attack.


Electromagnetic Pulse (EMP) is an intense energy field that can instantly overload or disrupt numerous electrical circuits at a distance. Modern high technology microcircuits are especially sensitive to power surges, and the possible vulnerability of U.S. civilian computer systems to the effects of EMP has been discussed in the media. EMP can be produced on a large scale using a single nuclear explosion, and on a smaller, non-nuclear scale using a device with batteries or chemical explosives. Several nations, including reported sponsors of terrorism, may currently have a capability to use EMP as a weapon for cyber warfare or cyber terrorism, to disrupt computers, communications systems, or parts of the U.S. critical infrastructure.

The threat of an attack against the United States involving EMP is hard to assess, but some observers indicate that it is growing along with worldwide access to newer technologies and the proliferation of nuclear weapons. In the past, the threat of mutually assured destruction provided a lasting deterrent against the exchange of multiple high-yield nuclear warheads. However, now a single, specially-designed low-yield nuclear explosion high above the United States, or over a battlefield, can produce an EMP effect that results in a widespread loss of electronics, but no direct fatalities, and may not necessarily evoke a large nuclear retaliatory strike by the U.S. military. This, coupled with the possible vulnerability of U.S. commercial electronics and U.S. military battlefield equipment to the effects of EMP, may create a new incentive for other countries to develop or acquire a nuclear capability.

Policy issues raised by this threat include (1) what is the United States doing to protect civilian critical infrastructure systems against the threat of EMP, (2) does the level of vulnerability of U.S. civilian and military electronics to large-scale EMP attack encourage other nations to develop or acquire nuclear weapons, and (3) how likely are terrorist organizations to launch a smaller-scale EMP attack against the United States?


Based upon reports to Congress from experts, in early 2005 the Senate Judiciary Committee's Subcommittee on Terrorism, Technology, and Homeland Security, chaired by Senator Jon Kyl, conducted hearings on a wide range of threats to the United States. One threat was EMPs and the possibility that an organization such as al-Qaeda could develop an EMP, mount it on a missile bought from a rogue nation such as North Korea, and launch it from an oceangoing platform over the United States.

On March 8, 2005, for example, the committee heard testimony from Dr. Peter M. Fonash, acting deputy manager of the National Communications System (NCS), now part of the U.S. Department of Homeland Security. (The purpose of the NCS, established in 1963 by President John F. Kennedy, is to maintain and protect the nation's telecommunications infrastructure in the event of emergencies such as war or terrorist attack. Part of its mandate is to conduct tests on EMPs and devise ways to mitigate the devices' effects.) Fonash noted that the NCS took part in the congressionally sponsored Commission to Assess the Threat from High Altitude Electromagnetic Pulse in 2004. The conclusion of the committee and the NCS, based on tests conducted in the late 1980s through 2000, was that the nation's electrical grid was highly vulnerable to the effects of EMPs. The telecommunications infrastructure, however, was less so because of improvements that have been made in current telecommunications switches and because the structures in which they are housed provide some shielding.

Fonash, however, did not discount the threat and pointed out that evolving technologies require the United States and other nations to continue research efforts.

Based on reports and assessments, many analysts worry that the threat of an EMP attack against the United States increases as global access to new technologies increase and as the proliferation of nuclear weapons continues.

Recognizing that these powerful EMPs were a byproduct of nuclear explosions, for decades American and allied scientists set out to harden the defenses of U.S. and NATO (North Atlantic Treaty Organization) electronic systems against disruption from nuclear explosions. As a specific response to terrorism, several U.S. agencies, including DARPA (Defense Advanced Research Projects Agency) and NIST (The National Institute of Standards and Technology), are continuing to conduct research on ways of protecting communications and computing infrastructure against the threat posed by EMPS.



21st Century U.S. Military Documents: EMP Attack, Electromagnetic Pulse Threats, Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse, High-Altitude Nuclear Weapon EMP Attacks. Washington, DC: Progressive Management, 2004.

Web sites

Northwestern University. "Electromagnetic Weapons: Electromagnetic Pulse." 2001–2002. <http://www.physics.northwestern.edu/classes/2001Fall/Phyx135-2/19/emp.htm> (accessed May 16, 2005).

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