Technology Explained – Pulse Bombs

The effectiveness of EMP as a military tool has steadily increased since the 1960s, when it was first discovered to have potential uses in this area. Confined at the time to nuclear means of generation, it never achieved great visibility and thus has remained one of the least publicised tools of the trade of Electronic Combat.

To understand the effectiveness of EMP in the modern military environment, we must first take a closer look at what it targets and the vulnerabilities involved.

The core of all modern electronic systems is the humble transistor, millions of which are present in the modern highly integrated chipsets which make up most contemporary computer equipment, and technologically related systems such as the signal processors and data processors which comprise the heart of modern military sensors.

Transistors have evolved considerably from their simple beginnings in the late forties and early fifties, but the basic physics behind semiconductor electronics have remained largely the same. The clever application of solid state physics has provided us with a blindingly fast electronic switch, which requires a miniscule amount of electromagnetic energy to switch itself on. Very high resolution photolithography and etching techniques have allowed thousands, and today millions of these switches to be squeezed into a single thumbnail or smaller sized slab of silicon, with intricate wiring interconnecting them to form whatever kind of electronic system is desired, for instance a memory or a microprocessor.

As electronic devices go, transistors are delicate little things, which are sensitive to heat, high energy radiation and high electrical voltages, all of which can cause an effect termed breakdown. While some transistors can recover from a breakdown and continue to function, in most transistors breakdown leads to a dramatic increase in the flow of electrical current through the device, causing it to rapidly overheat and destroy itself. What is important is that usually very little energy is required to precipitate a breakdown, but once the breakdown has occurred the power supply within the machine, computer or other, will provide ample energy to fry the broken down device, permanently.

The most common cause of damage to modern semiconductor devices today is static electricity. The small electrical charge held by a human body, at several kilovolts of potential, is often enough to seriously wound or kill a modern integrated circuit. Metal Oxide Semiconductor (MOS) technology devices, the heart of modern computers, are the most vulnerable and it is not far from the truth to say that a human touch can be deadly to the unshielded device.

Modern computer equipment hides these components inside metal or ceramic cases, which are shielded, these in turn hidden inside a shielded chassis. But, alas, wires must enter and exit the chassis to carry signals in and out of the machine and these wires are a path via which high voltage may insidiously enter the innards of the machine, to do its destructive work. Apertures such as cooling vents or gaps between panels may equally well open the chassis to destructive electrical fields.

It is this very basic vulnerability to high intensity electrical fields which renders modern electronics so vulnerable to EMP weapons.

An EMP weapon will produce a very short, but highly intense pulse of electromagnetic field which will, given conventional physics, propagate outward with ever diminishing intensity, at the speed of light. Basic physics dictate that if you place a wire into a changing electromagnetic field, an electrical voltage will appear, its size (amplitude) being proportional to the strength of the field, the parameters of the wire, and the rate of change of that field. Indeed, this is the basic principle upon which electrical machinery and antennas work.

The field strength produced by an EMP weapon and the sharpness of the pulse it produces however can produce voltages of hundreds to tens of thousands of volts even on very short wires, should these be within the effective radius of the weapon. Such voltages are, needless to say, lethal to modern solid state electronics. Disbelievers are advised to contemplate the effects of close lightning strikes upon household electronics, such as TVs, radios and computers (and most TV technicians have many such tales to tell …).

Unshielded electronics, such as commercial computer equipment, are particularly vulnerable, as all internal cables connected to a printed circuit board will in effect act as antennas to the EMP field, producing enough voltage to wound or kill the attached chips. The bigger problem however are cables into and out of equipment, as these have the length to pick up an appreciable spike of energy, acting in effect as antennas to the impinging field.

A nuclear EMP weapon detonated above an industrialised target will not only kill exposed electronics, it will also produce large transients on mains electrical power lines and telephone lines, the cables dutifully carrying the energy to whatever electronic or electrical device sits at the end of the cable. Burying or shielding equipment is thus not enough, as any electrically conductive path into a piece of equipment will be an entry point for the lethal electrical spike. This is why it is often sensible to physically unplug high value electronic items during a thunderstorm.

EMP Weapons and their Military Uses

The established military task of nuclear EMP weapons was the disabling of an opponent’s Command Control & Communications (C3) network and early warning radar network. EMP bombs may be delivered by any tactical aircraft equipped for loft bombing delivery, much like nuclear weapons. The combination of a strategic strike platform such as the F-111, supported by tankers, and armed with EMP bombs, provides the ability to cripple an opponent’s economy and air defence system from a substantial distance. This can provide substantial political leverage at a very low economic and political cost, and is thus a potent tool in the arsenal of any modern air force. (Defence PR)

Contemporary nuclear warfighting strategy with ballistic missiles typically involves the initial detonation of one or more EMP warheads in the upper atmosphere, above an opponent, so as to blind his radars and cripple if not wholly disable his communications equipment. These weapons are in turn followed by more conventional thermonuclear weapons which are air or surface burst against chosen targets, in line with the specific targeting strategy used.

EMP is a natural byproduct of a nuclear detonation but the magnitude of the EMP effect produced can be vastly enhanced by judicious choice of detonation altitude for the weapon. At very high altitudes, where the atmospheric density is very low, much of the high energy gamma radiation produced by a nuclear fission/fusion device will ionise the air molecules within reach of the weapon, and this ionisation effect will produce something akin to a vast lightning discharge in a cloud. Proper choice of altitude would allow a single high yield bomb to blanket an area the size of Victoria with an EMP sufficiently potent to do massive and indiscriminate electrical damage.

Because of the requirement for the use of a nuclear device to achieve this, EMP has fortunately not been used in combat yet. However the potency of EMP is well known, both the Russians and Americans learning the hard way during early atmospheric testing of nuclear weapons. Of note are the Teak programme trials, where low yield tactical nuclear devices for use in air defence missiles were tested. One such test, off the Hawaiian islands, caused massive electrical blackouts; fortuitously for Uncle Sam, transistors had yet to proliferate into the consumer marketplace so that commercial damage was limited.

On a lesser scale, many stories abound of damage to the automotive ignition systems of cars in the vicinity of US EMP testing facilities. These are test ranges where strategic weapons systems, such as the B-52 and B-1B, are subjected to conventionally produced EMP to verify the resilience of their electronics to damage.

Most recent years have seen a growth of interest in conventional EMP weapons, which do not require a nuclear warhead, and the effects of which are confined to much smaller radii of several miles. Open US sources indicate that research and development of such weapons is well advanced, specifically at Los Alamos and Eglin AFB in Florida, while reports from the UK indicate a growing interest in pursuing such development.

Conventional EMP weapons are based upon the idea of storing a large amount of electromagnetic energy in a device which can discharge it into its surroundings fast enough to produce a militarily useful EMP effect. Two general schemes have been openly discussed in the scientific literature, for production of militarily useful electromagnetic pulse effects.

The first scheme is based upon a device called a Flux Compression Generator or FCG. The idea behind an FCG is to produce an intense electromagnetic field in a coil, and to then rapidly compress the coil mechanically by imploding it with a jacket of plastic explosive around the coil. The enormous mechanical force which is exerted very rapidly by the explosive shock wave has the effect of transferring mechanical energy into the electromagnetic field. Experimental FCGs have produced electromagnetic pulses with power levels of tens of gigawatts of power (~50 GW or more). This is a non-trivial power level which can, if coupled into electronic equipment, cause damage on a wide scale.

The limitation of the FCG based scheme is that it produces a relatively low frequency pulse, which has a limited ability to couple into targets such as computers and radio comms equipment. Because most modern military equipment is, particularly if designed for strategic warfare, electromagnetically hardened against nuclear EMP attack, protective EMP suppressors may reduce the effect of the weapon. Another limitation of FCG based schemes is that the energy dumped by the weapon is unfocused, and at least 50% of it will be therefore wasted in radiation upward.

A means of substantially increasing the lethality of an FCG based electromagnetic weapon is to pump the output from the FCG into a high power microwave oscillator such as a vircator (Virtual Cathode Oscillator). Once the energy is converted into microwaves, it can be focused in one direction, as well as being far more able to couple into a target through holes and apertures. It has also been found that nuclear EMP hardening is typically ineffective against microwave frequency EMP. Therefore a microwave EMP weapon is substantially more lethal and controlled in its effect. Experiments using FCG pumped vircators have produced tens of gigawatts of microwave power. These are power levels capable of damaging targets over radii of hundreds of metres, limited by target electromagnetic hardness.

The non-nuclear nature of this family of weapons opens up new frontiers for their application. The publicly stated US policy on conventional EMP weapons is centred on their use against both military and civilian targets, as a non-lethal means of disabling an opponent’s warfighting capability and economy. To that effect some older USAF AGM-86 ALCM cruise missiles are being modified to accommodate such warheads. The modified weapons have a bulbous nose housing the weapon, and are reported to have received coatings of radar absorbent material to compensate the resulting increase in radar cross section.

While the US has not elaborated upon the internals of the ALCM warhead, US sources have indicated that the weapon uses an FCG, which supposedly radiates through a window in the nose of the missile. It is therefore reasonable to assume that the US weapon carries an FCG pumped microwave oscillator, which is probably a vircator operating in the 5 to 10 GHz microwave band, given quoted window dimensions.

An air force in possession of a conventional EMP capability has an effective tool for use in both tactical situations and strategic air warfare. Modern strategic air attack theory, based upon Warden’s ‘five rings’ model, sees a nation’s warfighting capability centred upon its leadership and C3 network about which in decreasing order of importance are positioned vital industries, road/rail/air transport, population and finally fielded military forces, which cannot effectively function without the innermost rings supporting them.

EMP weapons of sufficient potency delivered against strategic targets provide the means of concurrently attacking the C3 network, its supporting computer facilities, vital industries most of which cannot in this day and age function without computer support or electrical power, road/rail/air transport via the destruction of ignition systems and signalling equipment, the population, which is deprived of all of its domestic electronic creature comforts, and finally fielded forces, which cannot perform effectively once the bulk of their computer and communications equipment is rendered unserviceable.

Only a truly Third World basket weaving economy can escape the effects of EMP weapons, the use of which would be about as productive as ploughing up North Vietnam with Mk82s. Any moderately advanced economy would suffer badly, and Western economies with their abundance of computers and automated equipment could be crippled almost instantaneously.

As a tool for Electronic Combat operations against C3, surveillance and early warning radar and deployed SAM systems, EMP weapons are far more cost effective than expensive precision guided munitions, as their ability to blanket areas approaching square kilometres with varying intensities of EMP allow the concurrent attack of multiple targets. It is fair to say that EMP weapons are weapons of mass electrical destruction.

A conventional air battle against an industrialised opponent would typically involve an air control campaign, a strategic bombardment campaign and subject to the taste of the planners, an electronic combat campaign or at least intensive electronic combat operations in support of the two conventional campaigns. In a conventional scenario, C3 facilities would be attacked, concurrently with the Integrated Air Defence System and a range of strategic targets, the priority of attack being again subject to the preference of the planners.

With EMP weapons available for use, considerable economies of effort may be achieved in electronic combat operations, C3 attack and strategic strike. Judicious application of these weapons against concentrated facilities could concurrently disable co-located air defence equipment, C3 facilities such as telephone exchanges, and of course all computer and communications equipment within the target site. The prerequisite number of aircraft required for a knockout blow against the opponent’s air defence system and C3 facilities is thus greatly reduced, allowing many of these assets to be tasked with other, more resilient targets.

With proper planning and application, key industrial sites could be swiftly rendered inoperable, their eventual destruction by conventional laser guided bombs then only being a matter of assets becoming available once other more important targets have been dealt with. In this fashion, the size of the force required to achieve results such as those demonstrated in the Gulf could be reduced quite substantially, as the need to saturate defences in the early phase of the air battle is far lesser.

Military aircraft, airborne or on the ground, are typically no less vulnerable than surface targets. A sufficiently intensive EMP will damage or destroy the radar, communications equipment, engine electrical power generators, navigational aids and where fitted, electronic flight controls and engine controls. Given the right conditions, sufficiently intensive EMP could also trigger weapon fuse detonation.

Fig.2 Lethal Footprint of an Emp Weapon in Relation to Altitude

An EMP bomb using microwave technology can focus its delivered energy in a tightly confined pattern. Bomb lethality and area of coverage can be easily traded by adjusting the detonation altitude of the weapon fuse, thus allowing for attacks against softer civilian economic targets, as well as electromagnetically hard military targets with a single EMP bomb design.

Caught close enough to an EMP blast, a modern tactical fighter would simply fall out of the sky. If parked on the ground, it would more than likely be rendered very much unserviceable for some time.

An industrialised nation with a modern air defence system could therefore find itself in a similar situation to Iraq on that fateful January morning, when they found to their horror that most of their air defence system, communications and key industrial sites had been rendered inoperable in a matter of hours. At that point, the results are entirely predictable, with tactical fighters systematically destroying key targets by dropping precision guided munitions from medium altitudes, beyond the reach of AAA, day and night. The outcome is then inevitable.

The massed application of a suitable conventional EMP weapon would therefore achieve much of what the Allies achieved in the Gulf with about 4000 initial sorties. At most, hundreds of weapons would be required, to blanket the number of sites one would envisage, but what is significant is that this could be achieved with a force of very modest size. This opens up significant opportunities for smaller air forces such as the RAAF, being then able to tackle quite substantial opponents and very quickly reduce them down to a manageable and defeatable size.

Delivery methods for EMP weapons will require a standoff capability to ensure that the delivery platform does not suffer the same fate as its intended target. For an EMP bomb, a lofting technique such as is conventionally used for tactical nuclear weapon delivery is most appropriate. The tactical fighter would approach at low level up to the planned IP (initial point), then pull up steeply and maintain the appropriate nose-up attitude until the nav-attack computer releases the bomb, which would then fly a ballistic arc until impact, during which time the fighter has an opportunity to roll off the top and exit the area as quickly as possible. Fitting the EMP bomb with an appropriate drogue chute to control its rate of descent and equipping it with a radar altimeter fuse completes the scheme.

A somewhat more expensive scheme is to fit the warhead to a ballistic missile, in the class of the SS-20, Scud, Lance or Pershing. Similarly, cruise missiles may also be so equipped, as is happening in the US.

At the other end of the spectrum of delivery methods, one of course has the simple minded approach of using the weapon as a mine, and having terrorists infiltrate it and install it in an opponent’s territory. This could become a major problem should man-portable sized weapons be built and made available.

Another alternative form of weapon based upon this technology are microwave directed energy (DEW) or beam weapons. A microwave DEW would use an oscillator and power supply capable of continuous and repeated operation, unlike the one-shot oscillator and generator used in a bomb warhead. While a DEW produces a lot less energy, it would be used more selectively by illuminating a target directly and focusing all of the weapon’s output on the single target.

The most practical offensive use of a microwave DEW would be to fit a pod to a strike aircraft and using a direction finding receiver to cue a steerable antenna head in the pod, illuminate targets such as air defence radars, SAM systems and command posts. While this mode of attack lacks the shock effect of a large area coverage bomb, it is more discriminating and could potentially deliver more energy to a specific target. In addition, the method is more amenable to techniques such as frequency chirping, which can be used to improve power coupling into the target.

EMP weapons will confer a substantial advantage to their users, both in tactical and strategic operations, and will allow even substantial defences to be overwhelmed quickly and decisively, by a numerically inferior force. Because EMP weapons do not carry the political stigma of nuclear or chemical weapons, their initial use is unlikely to be withheld for political reasons. As they confer a military advantage not unlike that achieved by a pre-emptive nuclear strike, it is very reasonable to expect their pre-emptive use as a first strike weapon.

Defences Against EMP – Electromagnetic Hardening

The best defence against EMP is to prevent the microwave radiation or high voltage spikes from entering equipment in the first place. With fixed C3 sites, hardening can best be achieved by placing the whole site into a conductive metal enclosure, which forms a so-called Faraday cage. If the cage is built properly, the electric field produced by an EMP weapon cannot penetrate inside and the equipment is thus protected. However, signals must enter and exit the enclosure for it to be of any use, and in this instance wires must be replaced by optical fibres, which are electrical insulators and thus cannot carry weapon energy into the enclosure. The remaining problem is the electrical power feed to the equipment, which must be done via a suitably designed coupling transformer which is built to withstand incoming spikes without either breaking down or passing them into the cage. Hardening a fixed C3 site is thus straightforward, albeit expensive.

Equipment which by function must be exposed, such as radars, communications equipment, electronic warfare systems and computers used in platforms such as aircraft, requires an alternate technique. The individual item of equipment must have a suitably shielded chassis or enclosure, again forming a Faraday cage, but its power feed and signal connections must be equipped with suitable EMP arresting devices. A typical device of this variety will be a robust solid state switch or gas discharge device, which will break down and conduct when hit by an EMP spike, but which is designed to absorb the energy of the pulse safely and recover once it is dissipated. Where the pulse energy is sufficiently low, and the pulse very short, even simpler devices such as ferrite beads may be suitable, these having the effect of flattening and stretching the pulse in time such that only a lower and thus safe voltage may penetrate the equipment.

These techniques have been used in the past to harden strategic nuclear systems against nuclear EMP attack. Hardened systems have been tested in the US by wheeling a whole aircraft, such as a B-52, onto a gigantic wooden platform about which are strung cables connected to a large custom-built EMP generator. The whole aircraft is then subjected to a localised EMP effect of known intensity, to establish whether the hardening has been successful.

The problem, noted above, which has arisen with conventional microwave EMP weapons is that the pulse frequency parameters are very different and thus the EMP arresting devices tuned to nuclear EMP are quite ineffective when confronted with microwave EMP attack. US sources indicate that this may require substantial refitting of existing hardened systems.

While existing equipment can be hardened by retrofitting components, many devices cannot and a comprehensive hardening effort may require the redesign or replacement of a wide range of equipment types, or components thereof. The deployment of an EMP capability will therefore impose a significant economic burden upon the opposing side, should it decide to harden its systems in response.

The Australian Perspective

High Power Microwave (HPM) beam weapons, capable of delivering hundreds of kilowatts of power, are a potentially very effective electronic combat tool. This illustration depicts such a weapon used for suppression of hostile Command Control-Communications (C3) and air defences. The HPM beams would disrupt or electrically damage computers, communications and radar systems. The antenna head combines a HPM antenna, delivering the lethal beam, and a quartet of cavity-backed spiral antennas used to precisely point the main antenna at the offending emitter.

Australia is ill-equipped to deal with an EMP threat. While its situation is no different from that of other modern Western economies, insofar as civilian systems go, the ADF has expended little if any effort on EMP hardening (unless this is a uniquely well-kept secret). Whether the new fixed and mobile communications networks now being introduced have any hardening has not been publicised, but in line with the ADF’s established policy of not equipping for nuclear war, it is unlikely any of the equipment is so fitted. Should nuclear EMP have been hardened for, upgrading would be required regardless to cope with microwave attack.

Fortuitously, much of Telecom’s transcontinental communications links use optical fibres, with buried repeaters, and thus hardening these against EMP would require only a modest effort, mainly in protecting repeater power feed lines. Telephone exchanges are not so lucky, and with the proliferation of newer solid state digital exchanges the network has become substantially more vulnerable to EMP attack. Measures to arrest transients produced by lightning strikes are likely to be ineffective against microwave EMP attack.

Other systems of strategic importance which would require hardening include aviation navaids, primary and secondary radars, communications equipment, key computer facilities used by the ADF and government, and finally platforms.

It would be unwise to discount the potential threat of future EMP capable opponents. Regionally, China certainly has the capability to produce and deliver nuclear EMP weapons, as does India. Given time and effort, both nations could develop indigenous conventional EMP devices. All that is required is a small team of sufficiently bright physicists and engineers. Both nations possess adequate ballistic delivery systems.

Should there be problems with domestic development, the required components can be purchased commercially from sources within both the US and the CIS. The Russians are world leaders in explosively pumped flux compression generator technology (it could be said that they wrote the book on the topic), and are amongst the world’s most competent high power microwave engineers. Their economic circumstances are such that they would be unlikely to refuse any decent offer, and thus it is reasonable to expect that the technology will proliferate.

The possibility of ill-behaved countries like North Korea, Libya, Iraq and Iran possessing conventional EMP weapons is worrisome. A suitcase-sized EMP weapon activated in the central business district of a major Western capital city or economic centre could have devastating effects indeed. What is of concern is that many means of delivery exist, be they by air or missile, or by a terrorist on the ground. The latter is a distinct possibility, given the good availability of hardware (one Russian manufacturer has been offering a briefcase-sized microwave pulse generator which produces peak power levels of hundreds of kilowatts from an internal battery – this is a true “Luddite special” and it must be only a matter of time before it is used).

The next question is whether Australia should pursue the development and deployment of its own conventional EMP weapons. The answer is, without any doubt, yes! Having the capability to produce and use such weapons would not only vastly improve the ADF’s electronic combat and strategic air attack capability, but also provide such expertise to understand the effects of these devices and hence develop suitable hardening measures, over a period of time.

In comparison with other electronic combat systems such as jammers and anti-radiation missiles, EMP bombs are cheaper to build and maintain, being far simpler in design. Deploying an EMP bomb would immensely strengthen the RAAF’s electronic combat potential at a very modest cost, in comparison with the acquisition of standoff jamming aircraft and substantial stocks of ARMs such as HARM. Since an EMP bomb can be delivered by any tactical aircraft capable of loft bombing, both the F/A-18 and F-111 could be used as delivery platforms, not requiring sophisticated emitter locating systems required to target more complex guided weapons.

Possession of an EMP bomb would thus place the RAAF in the position of having a strategic capability to cripple both air defence systems and manufacturing economies, given the availability of delivery platforms. This would have the significant political benefit of increasing our regional military credibility, as well as giving the government the option of a graduated response in a confrontation. An opponent could be subjected to EMP attack initially, and once open to continuous air attack, placed under political pressure to concede.

Electromagnetic combat is by all means the growing trend in modern air warfare and the development of an Australian EMP weapons capability would be an extremely cost effective means of improving the RAAF’s potency in this critical area. Not to do so is to forgo a major capability that is quite easily within our reach.