Jeffrey LewisTalking Warheads on EMP

Patrick Disney, who runs the Talking Warheads blog, has a published an article in the Atlantic about the threat (or lack thereof) from EMP.  It is part of a broader paper he wrote in his graduate program.

Patrick asked to write something for the blog and, since Patrick is a nice fellow and EMP is an interesting topic, I agreed.  So, here you go!

There is a group of Washington policy specialists who put on a show every summer of which I enjoy being a spectator.  Each year this group proclaims that, far surpassing any other strategic threat facing America today, electromagnetic pulse (EMP) will be our country’s undoing.  Feature films are made, conferences are organized, and lobbyist breakfasts are shared.

But this year has witnessed a shift.  The message about the impending blackout has softened.  The jihadi boogeyman, who until recently was perched in a rowboat off the East coast ready to launch a scud, has vanished.  The new EMP monster under the bed is: solar weather?

NASA has warned that a significant solar event could take place during the solar maximum next year, with the potential to disrupt electronics on Earth. They’re taking the potential seriously enough that a group of scientists got together in June for the annual Space Weather Enterprise Forum (SWEF) to raise awareness of the threat to our technology-dependent society.  Organizations and individuals known for trumpeting the EMP threat to policymakers have also latched on, pointing to natural solar activity as the reason to protect the country’s electrical grid where previously their focus was on rogue ICBMs.  I have been puzzled, though, at what caused the sudden shift in messaging about the EMP issue.

It’s not in response to any blows landed by a counterattack from opposing interests.  To be honest, not a lot of folks have taken the EMP threat seriously enough to give it a thorough rebuttal.  Nick Schwellenbach from the Project on Government Oversight (POGO) is one exception, having penned the seminal beat-down in the Bulletin in 2005, which this blog duly covered. I myself have tried to dive into the issue as part of my graduate research, imagining various scenarios in which an electromagnetic pulse attack could seriously threaten the United States, its allies or its military.  And although I still maintain that EMP is, in general, a laughably overhyped “threat,” the issue deserves better treatment from the analytical community than it has gotten.

Shutting down “continental shutdown”

Mention EMP in Washington circles and you’ll likely hear about catastrophic failure of America’s electrical grid, or what some call “continental shutdown.”  [Mention EMP anywhere other than Washington and you’ll probably hear “That thing from Oceans’ 11?”]  In this scenario, a terrorist or rogue state launches a ballistic missile that detonates a couple hundred kilometers above Nebraska, which sends out a pulse of electrons that short-circuits regional power transformers continent-wide, which then causes fuel and food delivery to halt, which then causes millions to starve and the inevitable breakdown of society.  Next to zombies, EMP is one of the best horror stories around.

But this is by far the least likely scenario.  Imagine a terrorist who has somehow managed to acquire a nuclear warhead and an acceptable delivery vehicle with a range of a couple hundred miles capable of reaching an altitude of a couple hundred kilometers (essentially a modified SCUD).  Under what circumstances would a terrorist be unsatisfied with an old-fashioned, direct nuclear strike against a city?  If the goal is to crash the US economy, the terrorist could hit Wall Street; if the goal is mass social panic, hit a nuclear reactor.There isn’t a terrorist in the world who wouldn’t be content with killing hundreds of thousands of people and calling it a day.

Even if that weren’t enough, there are real reasons for an enemy not to be comfortable risking an attempt at an EMP.  For starters, the continental shutdown scenario depends inherently on cascading effects; as one key node in America’s infrastructure goes down, it is supposed to bring down others.  This sequence of events is complex and entirely unpredictable, making it impossible for the perpetrator to know how effective the attack will be in advance.  Furthermore, the effects of an EMP are not universal. The US first noticed that high-altitude nuclear detonations can produce gadget-frying EMPs after the Starfish Prime test in 1962, which knocked out street lights in Hawaii 800 miles away from the test. According to a 1989 Sandia National Lab report, however, only 1 percent of the lights went out.

When commissioned to do a study in 2007 by Instant Access Networks, the Sage Policy Group estimated the upper rangeof systems affected by an electromagnetic pulseto be around 70%; the lower range was around 5-10%.  That means that for any given EMP attack, somewhere between 5% and 70% of systems would be affected.  There’s no way to know for sure which end of that range it will actually be, making it much harder to pull the trigger in the first place.  And when the alternative is a direct nuclear strike against a city, why would a terrorist take his chances?


Infrastructure Percent of capacity damaged
Low case Mid case High case
Electric grid
Transformers 10% 40% 70%
Other 30% 40% 50%
Communications systems
Large 10% 20% 50%
Small 5% 20% 50%
All types 5% 20% 50%
Large 20% 45% 70%
Small 1% 2% 3%
Source: Charles Manto, Instant Access Networks


But that doesn’t mean it’s not tEMPting

The other, though far less well-publicized, scenario involves a state actor launching an EMP strike against the US’s superior (and technologically-dependent) military.  In 2005, the Defense Science Board created a task force to assess the military’s ability to function in post-Cold War nuclear environments.  In its report, the task force warned that a “general neglect of hardening as a requirement” as well as the shift to commercial-off-the-shelf (COTS) electronics have contributed to a growing fear that an EMP could seriously degrade the military’s operational effectiveness.  Therefore, as a way of degrading the capabilities of US troops massing on your border, an EMP could be an attractive option.

In fact, it’s an attractive enough warfighting tactic that General Norman Schwarzkopf was reported to have requested authorization to launch a nuclear EMP over Iraq at the start of the Gulf War.

Various constraints would have to be managed, of course.  For example the enemy would have to take care not to have his own critical technologies close enough to the blast that they too might be vulnerable.  Additionally, the decision to introduce nuclear weapons into a conflict with the US — even if there were no immediate casualties — risks eliciting a devastating US response, declaratory doctrine or no.  And of course, the US could repair or replace any damaged units relatively quickly, and would likely be more than willing to bear the costs of such a move because of that whole thing about a nuclear attack just launched against its forces.

All of this is to say that an EMP, though potentially damaging, would likely still not be a game changer for anybody facing the prospect of a war against the US military.


One big pain in the ASAT

With one potential exception.  So much of America’s advantage in today’s worldcomes from satellite technologylike GPS navigation, global communications, precision strike weapons, UAVs, and more.  What if an enemy carried out a high-altitude EMP detonation — like, really high — that could damage key American satellite systems?  Would that disable our ability to launch precision strike weapons anywhere we want and to communicate with assets around the world?

The short answer is no, but we reeeeeally don’t want to have to find out.

When a nuclear weapon detonates exo-atmospherically, it has two types of effects: long term and short term.  The short term effects are those you’d expect: blast, shockwave, fast-scatter EMP.  All of these propagate in line-of-sight, decreasing in strength over distance.  That means that, if a satellite isn’t directly close enough to the detonation — which most satellites would not be — it could escape relatively unscathed.

The potential danger to low-earth orbit (LEO) satellites comes from the lingering effects of a detonation.  A nuclear blast high up in the atmosphere increases the amount of ambient radiation already trapped in the lower of two radiation belts called the Van Allen belts.  When satellites are put in orbit, they are shielded against these naturally occurring radiation belts; the higher the orbit, the greater a satellite must be shielded because it will pass through more radiation on its way to its intended altitude.  For this reason, LEO satellites are not designed to withstand heavy amounts of radiation.

A problem arises from a high altitude nuclear detonation when the bomb raisesthe peak radiation levels in low Earth orbit — potentially by three or four orders of magnitude.   LEO satellites will therefore accumulate radiation damage much faster than they are designed for, meaning on-board electronics will degrade and the lifespan of the satellite will be drastically cut short.  These higher radiation levels encircle the Earth and can linger for anywhere from six months to two years.  Thus, even for satellites that are on the opposite side of the Earth at the time of detonation, their normal orbital patterns make them essentially swim in a pool of poison that shortens their operational lifespans.  In the words of a Defense Threat Reduction Agency (DTRA) study: “one low-yield (10-20 kt), high altitude (125-300 km) nuclear explosion could disable — in weeks to months — all LEO satellites not specifically hardened to withstand radiation generated by that explosion.”  Replacing these satellites quickly in the post-space shuttle era would be difficult or impossible, especially if Russia doesn’t feel like helping out our space program for some reason.

Fortunately, the US military possesses multiple redundant technologies that would preserve its core capabilities.  According to the DTRA study, if LEO satellites are degraded, satellite constellations in medium Earth or geosynchronous orbit may serve as workable substitutes and are out of the range of an Earth-based nuclear threat.  In addition, theatre capabilities like long endurance high altitude UAVs, wireless ground nets, and manned aircraft could be feasible alternatives for communications and tracking systems. Thus, the EMP would not eliminate the US’s precision strike capability, and nearly the entire range of options for a US retaliatory strike would remain intact.  However, the effectiveness of all US systems would not be guaranteed, and important civilian and military systems would likely suffer from limited bandwidth for months or even years after an exo-atmospheric nuclear detonation


Go forth and war-game

I’ll leave it to others to unpack the challenges to US deterrent credibility this sort of scenario poses.  But the prospects for an American response to an exo-atmospheric detonationare incredibly murky, especially when one imagines itin the context of a regional conflict that doesn’t involve the US,like India firing a stratospheric warning shot over Pakistan’s bow.  Plus, there are few other states that havemajor satellite holdings, making it difficult for the US to threaten in-kind retaliation.

All of this, in my humble opinion, makes for some great discussion about a fascinating topic.  So can we please stop with the Goldeneye nonsense now?


  1. Steve Tracton (History)

    Whether or not “Organizations and individuals known for trumpeting the EMP” have latched onto the threat to the electrical grid by solar activity, the threat from solar storms is real and probably much more likely than EMP from nuclear explosions. Moreover the possible impacts of severe solar (geomagnetic storms) are likely much more widespread and devastating to “life as we know it, independent of any effects on military necessities.

    I’ve been following the danger of space weather and written several blogs on the subject ( and links). I was at the June meeting and only one brief mention of EMP was made by someone in the audience. I got the impression this individual and others representing private firms were looking for research $$, perhaps because of not now being funded by DOD investigations of EMP. I’m also under the impression DOD is far ahead of the game in defending its own assets from geomagnetic storms than the civilian sector, but only because it’s incorporated implicitly in EMP defense.

  2. George William Herbert (History)

    The “post-shuttle era” comment about replacing low-altitude EMP / enhanced radiation belt damaged LEO sats is somewhat off base; by tons launched standards, the Shuttle wasn’t the predominant US (or, western) tons-launched capacity launch system.

    The hardest part is building replacement satellites, a process with prodigious lead times and capacity constraints, and the fact that everyone’s going to want rad-hard LEO sats after the first time this trick is done successfully… which means that all the rad-hard components pipelines will become yet another bottleneck.

    • user_hostile (History)

      Having designed rad-hard boards, you encounter another problem. You have an inverse relationship between functionality and rad-hardness. Which means if you want to have a lot of functionality for high-rad environments, your force to use to cobble simple components…which in turns starts lowering the overall reliability of the board.

      As for vendors who make rad hard components, your pretty limited in the components they provide. If it’s a electronic device that is universally accepted and used all over the industry, you might find it listed. Forget cutting edge, unless you’re the US government or have the deep pockets to throw money at it.

  3. yousaf (History)

    I wrote a two-part review of the “EMP threat” for Space Review:

    Nuclear EMP background:

    Solar/Geomagnetic EMP, and recommendations for protecting the grid:

    The bottom line is this: don’t throw the baby out with the bathwater. Just because the nuclear EMP threat is over-hyped does not mean there is no need for protecting the grid from strong geomagnetic storms. There is. I just gave a talk at the APS (American Physical Society) about this and am happy to share the slides with anyone who’s interested.

    One note, however: the type of threat from geomagnetic storms is of the slow, low-frequency E3 type and that from nuclear EMP is dominantly of the E1 type (esp. for mid-level yields) — so the types of protections needed for the grid and transformers are different.

    Here is the conclusion from the 2nd of my articles above:

    “The vulnerability of some of our infrastructure to nuclear EMP is real; however, the threat is overblown. A much greater threat to the US electricity-grid infrastructure is from a powerful once-in-a-century type solar storm. As the response to the geomagnetic threat would also address many of the vulnerabilities raised by the EMP commission, we can effectively kill two birds with one stone. However, the prioritization of our responses should emphasize the threat posed by geomagnetic storms, i.e. addressing the vulnerabilities to E3 type pulse should take precedence over E1 type pulses. Strategies for mitigating the risk from geomagnetic storms should be informed by a peer-reviewed study such as the Cold War era NAS report “Evaluation of Methodologies for Estimating Vulnerability to Electromagnetic Pulse Effects” [27] which provides much insight into how to go about protecting systems from nuclear EMP. An updated version of this peer-reviewed study, but tailored to the real geomagnetic threat, is now overdue.”

    I would add we need — urgently — to replace the ACE and SOHO satellites at L1. From my article —

    “Continued monitoring of the space environment is essential, but is seriously under-resourced. NASA’s Advanced Composition Explorer (ACE) satellite, which monitors energetic particles in the solar wind from a vantage point between the Earth and Sun (about 1.5 million kilometers sunward of Earth), was launched in August 1997 and is, according to the NAS report, “well beyond its planned operational life” with no plans on the books for a replacement even though “the requirement for a solar wind monitor… is particularly important”. The 12-year-old satellite, as well as another even older one named SOHO, “can fail any time, no one knows,” says Michael Hesse, director of the modeling center at Goddard Space Flight Center [26].

    Even with the current instrumentation in place and working, fully one-third of major storms arrive unheralded and almost one-quarter of the warnings turn out to be false alarms, according to the Space Weather Prediction Center (SWPC) [26]. Backup ACE and SOHO satellites should be funded and built as soon as feasible to offer critical lead time of impending geomagnetic storms. Although the Chinese are planning a similar monitoring satellite as part of their KuaFu space weather project, it will not be launched for several years. Encouragingly, the NASA Authorization Act of 2008 (Section 1101) charges the Office of Science and Technology Policy to work with NOAA, NASA, other federal agencies, and industry to develop a plan for sustaining solar wind measurements from an L1-based spacecraft. The urgency of this directive cannot be overstressed.”

  4. Davey (History)

    ‘Starfish Prime’ style nuclear generated EMP isn’t the only fish! There are a whole ecosystem of devices being developed which can generate terawatts of directed radio frequency energy at poorly protected modern electronics. To mention another arms-control-wonk contribution, it was Andrei Sakharov in the 1950s who devised a way to directly convert the energy from a kilo of TNT into an electromagnetic pulse. counterspace systems not using NEMP have also been widely developed (& deployed?)

  5. Mark Gubrud (History)

    The original campaign to hype the remote and unrealistic threat of nuclear EMP appears to have been politically motivated both to push missile defense, especially space-based missile defense, and to beat the “clock is ticking” war drums against Iran.

    But it’s a bit facile of Mr. Disney to dismiss the idea that a mortal enemy of the US and its empire would prefer to trigger a “continental shutdown” rather than nuke a city. The former would surely put us out of the World Police business, the latter would only make us madder than Hell.

    The “cascading effects” don’t seem so uncertain to me if an attacker can achieve a long-term shutdown of the electrical grid plus the destruction of a large fraction of computer and other electronic equipment. EMP is also not as poorly understood as Mr. Disney portrays it. A state actor would have a good idea of what effects would be achieved. Fortunately, from what I understand, it would take a megaton-class bomb at high altitude, or several, to achieve continent-wide effects with high assurance of profound and lasting damage. This is out of the reach of North Korea or Iran for the moment.

    As for terrorists, I’m sure al Qaeda would rather shut us down than just make us even more murderously angry, but as unlikely as it is for them to acquire a nuclear bomb, it is extremely unlikely for them to acquire a nuclear bomb on a ballistic missile that can carry it to high altitude over the United States.

    Also, it seems natural enough for people already alarmed about nuclear EMP to turn their concerns to the far more realistic threat of geomagnetic disruption from Solar coronal mass ejection. The need to ensure that we have adequate warning of any such events and that the grid is prepared to withstand them is critical and well worth the investment of many $Billions if necessary, given the frequency with which such events are known to occur. Can we learn something from Fukushima?

    • John Schilling (History)

      There is still a great deal of uncertainty regarding the effects of EMP, nuclear or otherwise. The degree and scale of testing required to have any confidence in the results is beyond even state actors.

      Just to start with, it is unclear that megaton-class weapons are required, or even useful – there is an argument that the primary of a fusion device will produce, in addition to a substantial EMP in its own right, enough induced ionization to render the upper atmosphere very briefly conductive enough to reflect the EMP produced by a large fusion explosion a microsecond or so later. If so, Starfish Prime showed us what ~50 kT of EMP is worth, and the 1.4 MT bit was a red herring.

      Or maybe not. Give me, oh, say two dozen assorted nuclear devices and IRBMs to loft them and I’ll pin that down for you…

      But that uncertainty is the problem. The most “optimistic” estimate of the effects of a properly executed high-altitude EMP attack would leave the United States materially incapable of conducting a major conventional military operation, and the most optimistic assessment of the political consequences would be that without a single American having been blasted, burnt, or irradiated to death the United States would not feel justified in nuking cities.

      Anything that causes a minor power to believe that it could cleverly use a small nuclear arsenal to preemptively remove the United States (or Russia, China, Europe) from the geopolitical equation and survive, is destabilizing in a way that a classic nuclear deterrent force is not. And while it would require an almost insane degree of optimism to believe this would actually work, nations which have been backed into a corner and presented with a “so crazy it just might work” way out, well, see the Japanese general staff in 1941…

    • Mark Gubrud (History)

      Sigh. I guess it was dicey of me to claim that nuclear EMP is well-understood by experts in the subject if I can’t claim to be one myself, but I can tell you that such experts do exist and they can tell you within useful bounds of uncertainty what sort of effects will be produced over what areas by which weapons at which altitudes.

  6. Allen Thomson (History)

    A brief introduction to the long-duration, non-EMP badness caused by a high altitude nuclear explosion:

  7. Andy (History)

    Mark your calendars! National EMP Recognition Day is coming August 15th!

  8. Loraine (History)

    Actually, solar scientists have been finding out that the sun seems to be going into a relatively quiet, inactive period as opposed to the normal maximum that would occur sometime around 2011/2012 according to what has been the regular cycle. They are not sure what this means for solar science, and my solar science is not that stellar (he he), but it seems that for satellites and other things which stand to be damaged by incoming charged particles from the sun, its a good thing.

    There are some interesting tales of solar science. One of the most interesting is the story of Richard Carrington, who in 1859 inadvertently witnessed the first observed coronal mass ejection, a super energetic cloud of charged particles that loops out from the sun. A good recounting of the story is on the NASA website.

    It is thought that Carrington witnessed one of the hottest ever flares, which if it happened today, would have much larger impacts than the flares we’ve seen in the modern era. From the recounting, “telegraph systems worldwide went haywire. Spark discharges shocked telegraph operators and set the telegraph paper on fire. Even when telegraphers disconnected the batteries powering the lines, aurora-induced electric currents in the wires still allowed messages to be transmitted.

    Full story, and other interesting tidbits are here:

  9. kme (History)

    What is the mechanism by which an exoatmospheric nuclear explosion generates a shockwave? Surely a shockwave requires a medium to travel in.

    • Jeffrey (History)

      Who said shockwave? I missed that …

    • kme (History)

      The third paragraph in the “One big pain in the ASAT” section:

      When a nuclear weapon detonates exo-atmospherically, it has two types of effects: long term and short term. The short term effects are those you’d expect: blast, shockwave, fast-scatter EMP.

    • Hairs (History)


      At the height at which a nuclear weapon would explode there is still enough atmosphere to support a shock front.

      The Voyager probes are currently traversing the heliopause, which is where the Sun’s magnetic field has a strength equal to the interstellar / galactic magnetic field, resulting in a shock front in the solar wind (something that has a density massively more tenuous than the atmosphere a hundred km or so above the Earth’s surface). Similarly the Earth has a large bow-shock where the solar wind meets the Earth’s magnetic field, which is at a point several thousand km from the Earth’s surface.

      The shock from a high altitude nuclear weapon is not the same as compression shock that you’d get at ground level, but it is a shockwave nonetheless.

      If you’d like to know about the subject (from a guy who’s a leading expert in space plasma and shocks) then try the very watchable lecture by Steve Schwartz at

  10. Hairs (History)

    As Yousaf writes, there is a substantial difference between the effects of nuclear weapons and solar flares / coronal mass ejections (CME), and I suspect that difference has skewed thinking in the defence and arms control community.

    Nuclear weapons produce effects predominantly within a few seconds (Compton scattering and all that), and therefore contingency planning – which has been of most interest to military people – has focused on the consequences of those short-term effects, which is the impact on electronics and communications. This is what Yousaf is referring to as E1.

    CMEs on the other hand predominantly have longer-term effects – measured over minutes and hours – whereby they displace the Earth’s magnetic field, and as this field moves about it induces current in long conductors i.e. transmission lines. This is what Yousaf refers to as E3.

    The problem is that the oscillation of the Earth’s field is so slow that it appears as if a d.c. current has been imposed on the transmission lines and everything connected to them. The effect of a d.c. offset is to saturate the iron cores of transformers, causing enormous MVAR swings on the grid (and MVAR swings equals voltage swings) and also causing heating in transformer components of up to 30 – 50 W/cm2 (about the same heat flux as your domestic cooker produces). Consequently transformers start to melt; this is what destroyed a big transformer in New Jersey state in the 13 March 1989 CME event, and similarly destroyed 14 transformers in South Africa in the 31 October 2003 event.

    From a purely military perspective the damage to transformers is not so important as the short-term effect on communications, but from the point of view of economic warfare the longer term damage is worse. The Halloween 2003 event set back South Africa’s electrification plans by a year or more, and that was just 14 pokey little transformers on a poorly interconnected grid.

    In the United States the Eastern Interconnection part of the grid carries about 610,000 MW, so as a rough approximation we can say that there will be about 2000 – 3000 big generator transformers connected to the grid. These things cost roughly $100,000 per MW, and for ones above about 100 MW you’ll have to wait at least a year, and usually closer to 18 months or two years, for one to be manufactured. Damaging even a few percent of the Eastern Interconnection’s transformers would exceed the world’s capacity to replace them in anything less than a year.

    The economic effects of such damage are hard to quantify, but two recent events give some insight. The first was Canada’s famous ice-storm of 1998, when all power lines but one into Montreal failed and other power lines around the region were badly affected. Water-pumping stopped, Montreal and Ottawa ceased functioning, and 4 million people were without electricity for up to one month. The other insight comes from the UK fuel protests in September 2000. In this case it was striking drivers and pickets that stopped fuel deliveries, but in the event of the collapse of the grid much the same effects would be seen because petrol stations use electric pumps to deliver fuel from underground storage tanks to the cars (and most stations do not have any kind of reserve pumping power). The UK fuel protests started on 8th September and (referring shamelessly to Wikipedia) just 5 days later the UK was in the following situation:

    “On 13 September 2000 the government announced that 5% of normal fuel deliveries were made, however other reports indicated only 3.8%. In Scotland only very limited supplies were being delivered for emergency use only. Three quarters of petrol stations were reported to be without fuel. Some hospitals cancelled non-essential operations due to staff difficulties in reaching work, ambulances were only able to answer emergency calls in most parts of the UK and the National Blood Service reported difficulties in moving supplies around the country. The government placed the National Health Service on red alert. Supermarkets began rationing food due to difficulties in getting food deliveries through and there were reports of panic buying. Sainsbury’s (a large supermarket chain) warned that they would run out of food within days having seen a 50% increase in their sales over the previous two days; Tesco and Safeway (also supermarkets) stated that they were rationing some items. The Royal Mail also reported they didn’t have enough fuel supplies to maintain deliveries. Schools began to close.”

    Unfortunately the fact that nuclear weapons have mostly E1 effects does not preclude E3 totally, and a sufficiently large explosion will cause a substantial local deflection of the Earth’s magnetic field, which will oscillate like a twanged guitar string for months.

    One other effect which has not been mentioned so far is that the control of the grid is done largely by a redundant system of power line carriers (i.e. sending signals down the transmission lines themselves) with a back-up microwave communications systems. But large E1 effects are likely to knock out both of these systems. In this case the automatic protection systems (e.g. current comparisons) will lose communication and as a fail-safe they’ll then trip the relevant section of the grid within a few tens of milliseconds.

    As John Schilling already notes, we don’t really know what would happen if there were some large high altitude nuclear explosions over, say, Toronto – but I’d certainly prefer not to find out. I also think the possibility of it happening, and the implementation of some relatively low cost protection – such as more and better surge arresters on transmission systems, should get more attention.

    After years of human losses, the UK was finally pushed into dealing with the IRA by the Baltic Exchange bomb and the subsequent Bishopsgate bomb, both of which targeted economic damage over deaths. Serbia capitulated over Kosovo in 1999 not because of deaths but because of economic damage. Similarly the west has largely departed Iraq, and is lining up to depart Afghanistan, not because we won militarily but because the economic costs are more than the allied nations are willing and able to bear. So in the world of asymmetric warfare we should not be surprised if actors such as Al Qaeda or North Korea dream more of exploding a crude device above our cities rather than trying to land a sophisticated device right on top of our hardened missile silos.

    • Anon (History)

      Not too stressed about AQ: e.g.

      “The full story is not out yet, but it seems breathtakingly unlikely that the miserable little group has had the time or inclination, let alone the money, to set up and staff a uranium-seizing operation, as well as a fancy, super-high-tech facility to fabricate a bomb. It is a process that requires trusting corrupted foreign collaborators and other criminals, obtaining and transporting highly guarded material, setting up a machine shop staffed with top scientists and technicians, and rolling the heavy, cumbersome, and untested finished product into position to be detonated by a skilled crew, all the while attracting no attention from outsiders.”

      Also read Mueller’s “Atomic Obsession”

      AQ may dream of an EMP strike — but it will remain a dream. If they get a low-yield bomb they will likely use it directly against a city not in an EMP strike about whose physics they would be at least as uncertain as US experts. Remember AQ is unlike able to make a Teller-Ulam high yield low weight device.

      From the 2nd of Yousaf’s review articles:

      “Even a “crude” U-type device is not all that “crude” and requires the concerted effort of skilled scientists and engineers. Any weapon produced by a terrorist cell would likely be a one of a kind and would have to remain untested. For a terrorist group to then mate this weapon to a ballistic missile and successfully carry out an EMP strike beggars belief. As John Pike, director of has said, “It is just very difficult to imagine how terrorists are going to be able to lay hands on a nuclear-tipped missile, and launch it and reprogram it in such a way that it would be a high-altitude burst like that.”

      Dr. Philip Coyle, former Pentagon director of operational test and evaluation, has stated that the EMP commission’s report appeared to “extrapolate calculations of extreme weapons effects as if they were a proven fact, and further to puff up rogue nations and terrorists with the capabilities of giants.” The 2009 Strategic Posture Commission puts it more delicately by saying that “the Commission is divided over how imminent a threat this is…”

      If a terrorist cell miraculously built such a weapon, they are likely to explode their “crown jewel” in a simple spectacular ground-burst that will destroy a large part of a city, and not risk the complications—and likely failure—of a lofted EMP strike that will, if all goes according to their plan, cause casualties via unpredictable secondary effects upon a limited part of some of the nation’s infrastructure. The risk versus reward calculation for both terrorists cells and so-called “rogue” states would almost certainly force their hand to a spectacular and direct ground burst in preference to a unreliable and uncertain EMP strike. A weapon of mass destruction is preferable to a weapon of mass disruption.

      A state would be highly unlikely to launch an EMP strike from their own territory because the rocket could be traced to the country of origin and would probably result in nuclear or massive conventional retaliation by the US. The EMP commission also considers adversarial nations carrying out a shipborne EMP attack that would be less traceable. However, even so, there would some small risk of trace-back that would give the leadership in such nations pause. While nuclear forensics are not well enough developed to assuredly ascribe the origin of a nuclear explosion, even their current state of development would, in some measure, dissuade the leaders of a nation from seriously contemplating such an attack. Furthermore, the US certainly has data, via its DSP satellites, on the infrared (IR) signatures of the rocket exhausts from the missiles of various countries. Though these signatures are probably virtually identical for the Scud/Shahab/No-dong family of missiles, the nations which may entertain such attacks do not necessarily know whether, e.g., the DSP data can discriminate between a NK Nodong versus an Iranian Shahabs, perhaps due to differences in fuel and/or subtle design idiosyncrasies. This is data only the US has, and it has an inherent deterrent value to nations thinking about launching an EMP strike via a ship-launched ballistic missile. This is almost certainly the case if, say, Iran were to use its solid rocket motor technology to launch such a strike—if and when Iran obtains nuclear weapons, of course. In such a case, the burn time-profile and solid-motor IR signatures could probably be used to tie the missile to a nation.

      Furthermore, the leaders of a nation contemplating such an attack would have to carefully consider what would happen in case the warhead was not delivered properly. If it fell short and/or did not explode, it may be possible for US engineers and scientists to ascribe a national origin given the forensic material. For the leadership of any nation to chance such an attack they must be almost suicidally optimistic: they would have to presume that everything would go perfectly. Even so, it may still be possible to identify the country of origin, which would invite massive US retribution.

      What about an adversarial nation “sub-contracting” its dirty work to a terrorist cell? Again, there would be substantial doubt in the nation’s leadership as to whether or not forensic evidence (whether the device exploded or not) could tie them to the weapon. In any case, as argued by Mueller [Ref 22, p. 163] it is highly unlikely that a nation would give one of its crown jewels to an unpredictable terrorist cell. At least in the case of Iran, this view is supported by in-depth research done by authors at the National Defense University, who conclude, “[W]e judge, and nearly all experts consulted agree, that Iran would not, as a matter of state policy, give up its control of such weapons to terrorist organizations and risk direct U.S. or Israeli retribution.”

      More importantly, the DoD itself has weighed in on the issue in its “Militarily Critical Technologies List”. This is a detailed compendium of the technologies the DoD assesses as critical to maintaining superior United States military capabilities. Part II, “Weapons of Mass Destruction Technologies,” addresses those technologies required for development, integration, or employment of biological, chemical, or nuclear weapons and their means of delivery against the US. This document states that “HEMP can pose a serious threat to U.S. military systems when even a single high-altitude nuclear explosion occurs. In principle, even a new nuclear proliferator could execute such a strike. In practice, however, it seems unlikely that such a state would use one of its scarce warheads to inflict damage which must be considered secondary to the primary effects of blast, shock, and thermal pulse. Furthermore, a HEMP attack must use a relatively large warhead to be effective (perhaps on the order of one megaton), and new proliferators are unlikely to be able to construct such a device, much less make it small enough to be lofted to high altitude by a ballistic missile or space launcher.”

      Lastly, General Robert T. Marsh, former Chairman of the President’s Commission on Critical Infrastructure Protection concluded (in 1997) that he did not, “see any evidence that suggests capabilities seriously threatening our critical infrastructure… There are many easier, less costly, and more dramatic ways for terrorists to use nuclear weapons than delivery to a high altitude. Such an event is so unlikely and difficult to achieve that I do not believe it warrants serious concern at this time.”

      And from the first of Yousaf’s articles:

      “Dependence of EMP on weapon yield and detonation height

      The EMP commission’s executive report expresses the concern that “terrorists or state actors that possess relatively unsophisticated missiles armed with nuclear weapons may well calculate that… they may obtain the greatest political-military utility from one or a few such weapons by using them—or threatening their use—in an EMP attack.” Given that scenario, such a warhead would likely be launched by one of the Scud/No-dong/Shahab family of missiles. Since the payload of such missiles is limited to ~1000 kilograms, and only relatively crude technologies are available to such actors, we can safely assume that the yield would be on the order of ~1 kiloton [22]. By comparison, the gun-type U-based Little Boy (15 kilotons) weighed 4 metric tons (4,000 kilograms), and the Fat Man (21 kilotons) was an implosion Pu-based device and weighed 4.6 metric tons.

      The EMP effects of a crude one-kiloton device , though still substantial, will be dramatically less than that of a one-megaton device. Firstly, a megaton-range EMP weapon is not very sensitive to the detonation altitude: any altitude between roughly 40 and 400 kilometers will yield a very strong E1 EMP pulse at ground level. On the other hand, the EMP effects of a smaller, one-kiloton warhead, is quite sensitive to the detonation altitude [16]. To boost the EMP lethality of a simple one-kiloton fission weapon, it must be detonated much lower than the hundreds of km that would expose the entire continental US to harmful electric fields. In fact, the “sweet spot” for maximizing the EMP lethality of such weapons would be a detonation altitude of about 40 kilometers—significantly higher, or lower, and the peak fields at ground level will decrease.

      This lower altitude implies a smaller region on the ground will exposed to high E-fields, as the “horizon” (the farthest extent on the ground with direct view of the detonation) is closer to ground-zero. For 40 kilometers altitude, the maximum extent of the induced EMP E1-fields is within a 725-kilometer radius. In reality, this is an overestimate because the EMP far from the peak field region is inherently limited in strength by the lower initial gamma-ray yield for a small device, and the distant pulse also has a wider (and, thus, less threatening) pulse time-profile. Although in standard texts it is shown that the E-fields expected at the periphery of the exposed ground regions are roughly half the peak fields, this applies to large (>100 kilotons) devices [5]. For smaller devices the peripheral fields will be expected to be significantly below half the peak field. A reasonable estimate for the extent for the destructive EMP E1 fields from a one-kiloton burst at 40 kilometers is about 10 times the altitude, or ~400 kilometers radius [Fig. 1].

      Thus, a standard “crude” one-kiloton device will not expose a very large area of the US to high E-fields, both because it will have to be detonated lower in the atmosphere to boost its EMP, and also because its EMP is inherently limited in strength. “

    • kme (History)

      I wonder if the effect on the Earth’s magnetic field could be used as part of the CTBT test detection efforts?

    • Jeffrey (History)

      Nuclear detection satellites have long had EMP detectors. Atmospheric tests, however, are not the most interesting verification challenge from a CTBT standpoint.

  11. The Launch Bunker (History)

    I read the report. Those 5-70% EMP damage figures were academic assumptions for the sake of an economic analysis study, not figures arrived at following a serious investigation. They are probably very inaccurate and it’s poor form that they were presented the way that they were(regardless of your point of view on the subject).

    I wrote a whole blog entry about this report:

  12. John (History)

    Slightly off topic, but upon my first browsing of the Talking Warheads blog I was appalled by the recent post on the “question” of whether Iran is seeking a nuclear weapon. It seemed strongly pro-Iranian and was laden with some fairly convoluted logic. I’m very surprised that it was linked on this blog but that post could’ve possibly been just a bad apple.

    • Jeffrey (History)

      I don’t think the post is “strongly pro-Iranian.”

      I am sure the Supreme Leader would not appreciate Patrick’s observation that “nuclear weapons are incapable of protecting against the single greatest threat to the regime’s existence: the Iranian people themselves.”

    • Amy (History)

      John, would you like to dispute the substance of what Patrick says in his excellent article on Iran?

      If you think he is pro-Iranian, then I guess our DNI is also pro-Iranian in which case you should lead an effort to strip our DNI of his security clearance.

      “Senator Levin, during the questions, got Clapper to confirm that the intelligence community has a “high level of confidence” that Iran “has not made a decision as of this point to restart its nuclear weapons program”

      Looks like Patrick’s article is the only one in Western hemisphere to agree with our DNI.

      Or maybe you can tell us what in Patrick’s superb article is wrong?

  13. Andrew Tubbiolo (History)

    Coming in late with this question. I hate to add to the EMP “The RF Sky is Falling”, hype, but has anyone considered that if the NORK’s set one off high in the atmosphere there’s an awful lot of CNC tooling in China and Japan that would fall in the footprint and or are attached to national grids that will be affected. Everyone likes to focus on command and control issues or financial issues. What happens when a huge chunk of manufacturing tools no longer work? Could data be so corrupted over such a large scale that manufacturing files for entire product lines might be lost?

    • John Schilling (History)

      Important data is usually backed up in a manner that is fairly secure against EMP, among other things. Ideally redundant and geographically dispersed; not everybody takes things to that extreme but I’d be surprised if data loss were the real problem.

      The tooling itself, yes, that could be a problem. Lots of embedded microcontrollers, and while most of them have been tested against e.g. lightning-strike EMP, nuclear EMP is sufficiently different to give cause for concern.

    • Hairs (History)


      I think a bigger effect would come from loss of synchronisation. A great many processes now – especially in power plants and refineries – rely on their control timings being synchronised to GPS time. If GPS is lost, either because ionisation causes the atmosphere to become radio opaque or because some of the satellites themselves are damaged, then controllers will either revert to their internal clocks or else they’ll cease working altogether.

      In some cases the process timings will drift apart, and in fields like combustion stability control a few milliseconds of drift will be enough for the process to either fail or trip; in other cases detection of a loss of synchronisation will cause a shutdown into a failsafe condition. Either way, it would be difficult or impossible to re-start the process until synchronisation is recovered.

      At the moment it’s far cheaper to put a GPS receiver into pieces of equipment separated by 100 metres or so than it is to run a synchronising cable or hard-wired signal between the two. Consequently the more modern the process the more susceptible it is likely to be to the loss of an external (satellite) time signal. Of course, if there’s no physical damage then non-satellite synchronisation can be retro-fitted and the process started up again, but that takes some time – at least a few days for something small if you haven’t got the cable, and probably several weeks if you have a whole refinery, power station, oil production platform, etc to do.

      The same goes for automatic robots and positioning systems. My understanding is that modern container ports e.g. Singapore, Hamburg, Rotterdam, etc rely a lot on a form of differential GPS for automatic tracking of containers, cranes and transport robots. I presume that if these were heavily damaged by an EMP, or if the satellites were no longer visible, then container shipping around the world would be significantly disrupted.

Pin It on Pinterest