August 3, 2004 | Backgrounder on National Security and Defense
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A nuclear-generated electromagnetic pulse "is one of a small number of threats that has the potential to hold our society seriously at risk and might result in defeat of our military forces." The Commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack announced this startling conclusion in a July 22 report to Congress.1 This alarming report clears the way for Congress to debate more seriously the most effective measures to meet the threat of an EMP attack.
In addition to the ability to kill thousands of people instantly, nuclear weapons have another, equally crippling capability to destroy or disrupt power grids, electronic systems, and communications in an entire country, while sparing the lives of its people--at least initially. Specifically, a nuclear bomb detonated above the earth's atmosphere would create a split-second electromagnetic pulse, similar to an extremely high-energy radio wave. For example, a single nuclear weapon detonated at an altitude of 500 kilometers could produce an EMP that would blanket the entire continental United States, potentially damaging or destroying military forces and civilian communications, power, transportation, water, food, and other infrastructure essential to modern society.2 Although recent changes in homeland security policy would decrease the severity of such an attack, recovery could still take years. In a congressional hearing on the EMP threat, chaired by Representative Roscoe Bartlett (R-MD), Dr. Lowell Wood of the Lawrence Livermore National Laboratory described the effect of an EMP attack as instantly regressing a country dependent on 21st century technology by more than 100 years.3
Although the EMP threat has been the focus of significant government-funded research and testing over the past 30 years, most of those efforts were conducted during the Cold War and focused on hardening strategic systems against a massive nuclear attack by the Soviet Union. Far fewer resources have been dedicated to examining the potential vulnerability of the U.S. civilian and industrial infrastructure to an EMP attack. Moreover, since the end of the Cold War, U.S. military and civilian systems have become increasingly dependent on advanced electronics that are potentially more vulnerable than older electronics to EMP attack--a trend that will likely continue.
Recognizing the potential of this powerful nuclear phenomenon, Congress established the EMP Commission under the National Defense Authorization Act of 2001 in order to provide an independent assessment of this threat against the United States. The authorizing provision directed that the EMP Commission investigate and report to Congress its findings and recommendations for the United States concerning four aspects of the EMP threat:
Little has been done to safeguard U.S. electrical systems from the EMP threat beyond simply protecting the nation's nuclear war-fighting infrastructure--and even that is not as secure as it once was. During the Cold War, only the Soviet Union--and to a lesser extent China--had the ability to mount an EMP attack against the United States. If one of those countries had launched an EMP attack, it would most likely have been the initial salvo of a larger nuclear attack. Therefore, it made little sense to separate an EMP attack from general nuclear war. Because most civilian and non-strategic military equipment would be destroyed or of no use during a full-scale nuclear exchange, there was no requirement to protect civil infrastructure from an EMP.
Today, the proliferation of nuclear technology and ballistic missiles has changed the nature of the EMP threat. A high-altitude EMP explosion over the continental United States or a battle space must be understood as a separate and unique threat that requires a unique response. Understanding both the effects of EMP, as well as America's vulnerability, is the first step in addressing the threat.
The scientific principles behind generating a high-altitude EMP are relatively simple. If a nuclear weapon is detonated between 25 miles and 300 miles above the earth's surface, the radiation from the explosion interacts with air molecules to produce high-energy electrons that speed across the earth's magnetic field as an instantaneous, invisible electromagnetic pulse.5
An EMP can have devastating consequences for developed countries because any metallic conductor in the affected area 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 likely be damaged or disrupted by the intense energy pulse. Indeed, depending on the strength of the pulse and the vulnerability of the equipment, the effects could range from a passing interference to completely melting the electrical components.
An EMP attack damages all unprotected electronic equipment within the blast's "line of sight" (the EMP's "footprint" on the earth's surface). The size of the footprint is determined by the altitude of the explosion. The higher the altitude, the greater the land area affected. A Scud-type ballistic missile launched from a vessel in U.S. coastal waters and detonated at an altitude of 95 miles could degrade electronic systems across one-quarter of the United States. A more powerful missile launched from North Korea could probably deliver a warhead 300 miles above America--enough to degrade the electronic systems across the entire continental United States.
Furthermore, a nuclear weapon with only a low explosive yield could be designed to generate a strong EMP. In fact, crude weapons with low yields, such as those used against Japan in World War II, would have ample power to generate an EMP over the entire continental United States.
Under what circumstance would the United States be attacked with an EMP? Possible scenarios include a rogue state interested in demonstrating its ability to strike U.S. territory or a country that wants to give itself an advantage in a regional conflict by crippling U.S. military and other allied forces that are more dependent on advanced electronics.
Although the threat of a high-altitude EMP attack against America existed during the Cold War, the likelihood may be much greater today.6 During the Cold War, an EMP attack was viewed as the first step in launching a nuclear war. However, it was never tried because the threat of massive nuclear retaliation, the central tenet of the mutual assured destruction doctrine, provided an effective deterrent. Although China and Russia both maintain the ability to launch major nuclear strikes against the United States, the Cold War dynamic that made the doctrine of mutual assured destruction relevant is largely gone from today's strategic calculations.
The proliferation of weapons of mass destruction (WMDs), the rise of powerful non-state actors, and the evolving strategic relationships with countries like China and Russia have made the threat more difficult to assess. In reality, the U.S. simply cannot rely on the old tools of deterrence to compel threatening regimes not to attack the United States or its interests. As demonstrated on September 11, 2001, the Cold War deterrent of massive retaliation does not work.
The emergence of nuclear rogue states results in a completely new strategic calculation. Since no rogue nation has the capacity to fight a general nuclear war, an EMP blast would not be a precursor of full-scale nuclear war. Furthermore, since an EMP blast is unlikely 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. It is simply unclear how the U.S. would respond to such an attack.
The difficulty of developing a clear response to EMP is due primarily to the unique nature of the threat. It is unclear, for example, what would constitute a "proportional response" to an explosion that takes place in space without being seen or heard, yet instantaneously devastates society or a military force while resulting in no initial loss of life or physical destruction. Furthermore, there is a dearth of academic or legal analysis by which to guide such policies because, until very recently, few took the threat seriously. This is especially so in the context of rogue states or transnational groups.
The simple motivation for a rogue state to use its limited nuclear arsenal in an EMP strike against the United States is that an EMP attack maximizes the impact of a few warheads while minimizing the risk of retaliation. This profound decrease in risk for rogue leaders could impel them to use EMP to offset overwhelming U.S. conventional power on the battlefield. While EMP may not precede general nuclear war, it could be used as an opening salvo in a conventional war. Nations with small numbers of nuclear missiles, such as North Korea or Iran, may consider an EMP attack against U.S. forces in a region, to degrade the U.S. military's technological advantage, or against the United States' national electronic infrastructure.
Furthermore, an EMP attack using a few nuclear weapons could theoretically damage the entire continental United States, far exceeding the impact of using those same warheads against specific U.S. cities or installations. Likewise, an EMP attack could degrade the U.S. armed forces throughout an entire region. Because America's response to an EMP attack by a rogue state is unclear and because EMP attacks are less risky for rogue states, such attacks are far more likely in this era of nuclear weapons proliferation than during the Cold War.
Unfortunately, hardening systems is difficult and expensive. To protect electronics infrastructure, entire systems must be encased in a metallic shield to prevent 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 need to be protected. Continuing efforts to replace copper communications cable with fiber optic cable will significantly reduce overall EMP vulnerability. To ensure that the protection lasts for the lifetime of the equipment, system maintenance and testing should be performed regularly. If a system is modified, repaired, or serviced, its EMP vulnerability should be reassessed.
All of these steps can be affordable. Assuming these protections are engineered into a product or structure from the outset, these protections 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, former Deputy Director of the now abolished Defense Special Weapons Agency, such hardening is needed:
Systems, such as commercial power grids [and] telecommunications networks re-main vulnerable to widespread outages and upsets due to high altitude EMP. While DOD hardens assets it deems vital, no comparable civil program exists.7
By itself, a policy guaranteeing significant retaliation may not deter all hostile groups from using EMP, but it may deter some. Better yet, a policy to retaliate combined with other actions--such as installing active defenses, increased passive defenses, and assuring military survivability--would decrease the likelihood of an EMP attack against the United States because such measures would make a strike less likely to succeed. If it did succeed, the consequences for the United States would be minimal. Thus, the value of an EMP strike would be greatly reduced, but the risk of launching an attack would be greatly increased because the U.S. would not only have a policy to retaliate, but also the capability.
As the EMP Commission reported, an EMP attack on America is a serious possibility and one for which the United States is unprepared. While the world focuses on WMDs and ballistic missiles, it is imperative that an EMP attack be considered with equal weight. The profound impact that an EMP attack would have on a developed, modern, electronically oriented country forces nations in similar positions to reassess their own protection against such attack.
Looking toward the future, America should consider its options for protecting its infrastructure against such a debilitating attack. Those options are limited, but include deploying an effective missile defense system and hardening electronic systems against EMP. As the commission indicated, the implications of an EMP attack need to be assessed further with greater severity and inevitability as America considers possible protective actions against this threat.
Jack Spencer is Senior Policy Analyst for Defense and National Security in the Kathryn and Shelby Cullom Davis Institute for International Studies at The Heritage Foundation.
2. "Title XIV--Commission to Assess the Threat to the United States From Electromagnetic Pulse (EMP) Attack: Overview," in National Defense Authorization Act for Fiscal Year 2001, Public Law 106-398, June 2003.
5. For a scientific description of the physics of high-altitude electromagnetic pulses, see Gary Smith, "Electromagnetic Pulse Threats," testimony before the Subcommittee on Military Research and Development, Committee on National Security, U.S. House of Representatives, July 16, 1997.
7. Dr. George W. Ullrich,
statement in Hearing, Threat Posed by Electromagnetic Pulse (EMP)
to U.S. Military Systems and Civil Infrastructure, Subcommittee on
Military Research and Development, Committee on National Security,
U.S. House of Representatives, 105th Cong., 1st Sess., July 16,
1997, p. 23, at
has197010_0f.htm (July 30, 2004).