A WEAPON OF ELECTRONIC MASS DESTRUCTION
WRITTEN BY CARLO KOPP, DEFENSE ANALYST, MELBOURNE,
High Power Electromagnetic Pulse generation techniques and High
Power Microwave technology have matured to the point where practical
E-bombs (Electromagnetic bombs) are becoming technically feasible,
with new applications in both Strategic and Tactical Information
Warfare. The development of conventional E-bomb devices allows their
use in non-nuclear confrontations. This paper discusses aspects
of the technology base, weapon delivery techniques and proposes
a doctrinal foundation for the use of such devices in warhead and
The prosecution of a successful Information Warfare (IW) campaign
against an industrialised or post industrial opponent will require
a suitable set of tools. As demonstrated in the Desert Storm air
campaign, air power has proven to be a most effective means of inhibiting
the functions of an opponent's vital information processing infrastructure.
This is because air power allows concurrent or parallel engagement
of a large number of targets over geographically significant areas.
While Desert Storm demonstrated that the application of air power
was the most practical means of crushing an opponent's information
processing and transmission nodes, the need to physically destroy
these with guided munitions absorbed a substantial proportion of
available air assets in the early phase of the air campaign. Indeed,
the aircraft capable of delivering laser guided bombs were largely
occupied with this very target set during the first nights of the
The efficient execution of an IW campaign against a modern industrial
or post-industrial opponent will require the use of specialised
tools designed to destroy information systems. Electromagnetic bombs
built for this purpose can provide, where delivered by suitable
means, a very effective tool for this purpose.
The EMP Effect
The ElectroMagnetic Pulse (EMP) effect was first observed during
the early testing of high altitude airburst nuclear weapons. The
effect is characterised by the production of a very short (hundreds
of nanoseconds) but intense electromagnetic pulse, which propagates
away from its source with ever diminishing intensity, governed by
the theory of electromagnetism. The ElectroMagnetic Pulse is in
effect an electromagnetic shock wave.
This pulse of energy produces a powerful electromagnetic field,
particularly within the vicinity of the weapon burst. The field
can be sufficiently strong to produce short lived transient voltages
of thousands of Volts (ie kiloVolts) on exposed electrical conductors,
such as wires, or conductive tracks on printed circuit boards, where
It is this aspect of the EMP effect which is of military significance,
as it can result in irreversible damage to a wide range of electrical
and electronic equipment, particularly computers and radio or radar
receivers. Subject to the electromagnetic hardness of the electronics,
a measure of the equipment's resilience to this effect, and the
intensity of the field produced by the weapon, the equipment can
be irreversibly damaged or in effect electrically destroyed. The
damage inflicted is not unlike that experienced through exposure
to close proximity lightning strikes, and may require complete replacement
of the equipment, or at least substantial portions thereof.
Commercial computer equipment is particularly vulnerable to EMP
effects, as it is largely built up of high density Metal Oxide Semiconductor
(MOS) devices, which are very sensitive to exposure to high voltage
transients. What is significant about MOS devices is that very little
energy is required to permanently wound or destroy them, any voltage
in typically in excess of tens of Volts can produce an effect termed
gate breakdown which effectively destroys the device. Even if the
pulse is not powerful enough to produce thermal damage, the power
supply in the equipment will readily supply enough energy to complete
the destructive process. Wounded devices may still function, but
their reliability will be seriously impaired. Shielding electronics
by equipment chassis provides only limited protection, as any cables
running in and out of the equipment will behave very much like antennae,
in effect guiding the high voltage transients into the equipment.
Computers used in data processing systems, communications systems,
displays, industrial control applications, including road and rail
signalling, and those embedded in military equipment, such as signal
processors, electronic flight controls and digital engine control
systems, are all potentially vulnerable to the EMP effect.
Other electronic devices and electrical equipment may also be
destroyed by the EMP effect. Telecommunications equipment can be
highly vulnerable, due to the presence of lengthy copper cables
between devices. Receivers of all varieties are particularly sensitive
to EMP, as the highly sensitive miniature high frequency transistors
and diodes in such equipment are easily destroyed by exposure to
high voltage electrical transients. Therefore radar and electronic
warfare equipment, satellite, microwave, UHF, VHF, HF and low band
communications equipment and television equipment are all potentially
vulnerable to the EMP effect.
It is significant that modern military platforms are densely packed
with electronic equipment, and unless these platforms are well hardened,
an EMP device can substantially reduce their function or render
The Technology Base for Conventional Electromagnetic
The technology base which may be applied to the design of electromagnetic
bombs is both diverse, and in many areas quite mature. Key technologies
which are extant in the area are explosively pumped Flux Compression
Generators (FCG), explosive or propellant driven Magneto-Hydrodynamic
(MHD) generators and a range of HPM devices, the foremost of which
is the Virtual Cathode Oscillator or Vircator. A wide range of experimental
designs have been tested in these technology areas, and a considerable
volume of work has been published in unclassified literature.
This paper will review the basic principles and attributes of
these technologies, in relation to bomb and warhead applications.
It is stressed that this treatment is not exhaustive, and is only
intended to illustrate how the technology base can be adapted to
an operationally deployable capability.
Explosively Pumped Flux Compression Generators
The explosively pumped FCG is the most mature technology applicable
to bomb designs. The FCG was first demonstrated by Clarence Fowler
at Los Alamos National Laboratories (LANL) in the late fifties.
Since that time a wide range of FCG configurations has been built
and tested, both in the US and the USSR, and more recently CIS.
The FCG is a device capable of producing electrical energies of
tens of MegaJoules in tens to hundreds of microseconds of time,
in a relatively compact package. With peak power levels of the order
of TeraWatts to tens of TeraWatts, FCGs may be used directly, or
as one shot pulse power supplies for microwave tubes. To place this
in perspective, the current produced by a large FCG is between ten
to a thousand times greater than that produced by a typical lightning
The central idea behind the construction of FCGs is that of using
a fast explosive to rapidly compress a magnetic field, transferring
much energy from the explosive into the magnetic field.
The initial magnetic field in the FCG prior to explosive initiation
is produced by a start current. The start current is supplied by
an external source, such a a high voltage capacitor bank (Marx bank),
a smaller FCG or an MHD device. In principle, any device capable
of producing a pulse of electrical current of the order of tens
of kiloAmperes to MegaAmperes will be suitable.
A number of geometrical configurations for FCGs have been published.
The most commonly used arrangement is that of the coaxial FCG. The
coaxial arrangement is of particular interest in this context, as
its essentially cylindrical form factor lends itself to packaging
In a typical coaxial FCG , a cylindrical copper tube forms the
armature. This tube is filled with a fast high energy explosive.
A number of explosive types have been used, ranging from B and C-type
compositions to machined blocks of PBX-9501. The armature is surrounded
by a helical coil of heavy wire, typically copper, which forms the
FCG stator. The stator winding is in some designs split into segments,
with wires bifurcating at the boundaries of the segments, to optimise
the electromagnetic inductance of the armature coil.
The intense magnetic forces produced during the operation of the
FCG could potentially cause the device to disintegrate prematurely
if not dealt with. This is typically accomplished by the addition
of a structural jacket of a non-magnetic material. Materials such
as concrete or Fibreglass in an Epoxy matrix have been used. In
principle, any material with suitable electrical and mechanical
properties could be used. In applications where weight is an issue,
such as air delivered bombs or missile warheads, a glass or Kevlar
Epoxy composite would be a viable candidate.
It is typical that the explosive is initiated when the start current
peaks. This is usually accomplished with a explosive lense plane
wave generator which produces a uniform plane wave burn (or detonation)
front in the explosive. Once initiated, the front propagates through
the explosive in the armature, distorting it into a conical shape
(typically 12 to 14 degrees of arc). Where the armature has expanded
to the full diameter of the stator, it forms a short circuit between
the ends of the stator coil, shorting and thus isolating the start
current source and trapping the current within the device. The propagating
short has the effect of compressing the magnetic field, whilst reducing
the inductance of the stator winding. The result is that such generators
will producing a ramping current pulse, which peaks before the final
disintegration of the device. Published results suggest ramp times
of tens to hundreds of microseconds, specific to the characteristics
of the device, for peak currents of tens of MegaAmperes and peak
energies of tens of MegaJoules.
The current multiplication (ie. ratio of output current to start
current) achieved varies with designs, but numbers as high as 60
have been demonstrated. In a munition application, where space and
weight are at a premium, the smallest possible start current source
is desirable. These applications can exploit cascading of FCGs,
where a small FCG is used to prime a larger FCG with a start current.
Experiments conducted by LANL and AFWL have demonstrated the viability
of this technique.
The principal technical issues in adapting the FCG to weapons
applications lie in packaging, the supply of start current, and
matching the device to the intended load. Interfacing to a load
is simplified by the coaxial geometry of coaxial and conical FCG
designs. Significantly, this geometry is convenient for weapons
applications, where FCGs may be stacked axially with devices such
a microwave Vircators. The demands of a load such as a Vircator,
in terms of waveform shape and timing, can be satisfied by inserting
pulse shaping networks, transformers and explosive high current
Explosive and Propellant Driven MHD Generators
The design of explosive and propellant driven Magneto-Hydrodynamic
generators is a much less mature art that that of FCG design. Technical
issues such as the size and weight of magnetic field generating
devices required for the operation of MHD generators suggest that
MHD devices will play a minor role in the near term. In the context
of this paper, their potential lies in areas such as start current
generation for FCG devices.
The fundamental principle behind the design of MHD devices is
that a conductor moving through a magnetic field will produce an
electrical current transverse to the direction of the field and
the conductor motion. In an explosive or propellant driven MHD device,
the conductor is a plasma of ionised explosive or propellant gas,
which travels through the magnetic field. Current is collected by
electrodes which are in contact with the plasma jet.
The electrical properties of the plasma are optimised by seeding
the explosive or propellant with with suitable additives, which
ionise during the burn. Published experiments suggest that a typical
arrangement uses a solid propellant gas generator, often using conventional
ammunition propellant as a base. Cartridges of such propellant can
be loaded much like artillery rounds, for multiple shot operation.
High Power Microwave Sources - The Vircator
Whilst FCGs are potent technology base for the generation of large
electrical power pulses, the output of the FCG is by its basic physics
constrained to the frequency band below 1 MHz. Many target sets
will be difficult to attack even with very high power levels at
such frequencies, moreover focussing the energy output from such
a device will be problematic. A HPM device overcomes both of the
problems, as its output power may be tightly focussed and it has
a much better ability to couple energy into many target types.
A wide range of HPM devices exist. Relativistic Klystrons, Magnetrons,
Slow Wave Devices, Reflex triodes, Spark Gap Devices and Vircators
are all examples of the available technology base [GRANATSTEIN87,
HOEBERLING92]. From the perspective of a bomb or warhead designer,
the device of choice will be at this time the Vircator, or in the
nearer term a Spark Gap source. The Vircator is of interest because
it is a one shot device capable of producing a very powerful single
pulse of radiation, yet it is mechanically simple, small and robust,
and can operate over a relatively broad band of microwave frequencies.
The physics of the Vircator tube are substantially more complex
than those of the preceding devices. The fundamental idea behind
the Vircator is that of accelerating a high current electron beam
against a mesh (or foil) anode. Many electrons will pass through
the anode, forming a bubble of space charge behind the anode. Under
the proper conditions, this space charge region will oscillate at
microwave frequencies. If the space charge region is placed into
a resonant cavity which is appropriately tuned, very high peak powers
may be achieved. Conventional microwave engineering techniques may
then be used to extract microwave power from the resonant cavity.
Because the frequency of oscillation is dependent upon the electron
beam parameters, Vircators may be tuned or chirped in frequency,
where the microwave cavity will support appropriate modes. Power
levels achieved in Vircator experiments range from 170 kiloWatts
to 40 GigaWatts over frequencies spanning the decimetric and centimetric
The two most commonly described configurations for the Vircator
are the Axial Vircator (AV) (Fig.3), and the Transverse Vircator
(TV). The Axial Vircator is the simplest by design, and has generally
produced the best power output in experiments. It is typically built
into a cylindrical waveguide structure. Power is most often extracted
by transitioning the waveguide into a conical horn structure, which
functions as an antenna. AVs typically oscillate in Transverse Magnetic
(TM) modes. The Transverse Vircator injects cathode current from
the side of the cavity and will typically oscillate in a Transverse
Electric (TE) mode.
Technical issues in Vircator design are output pulse duration,
which is typically of the order of a microsecond and is limited
by anode melting, stability of oscillation frequency, often compromised
by cavity mode hopping, conversion efficiency and total power output.
Coupling power efficiently from the Vircator cavity in modes suitable
for a chosen antenna type may also be an issue, given the high power
levels involved and thus the potential for electrical breakdown
The Lethality of Electromagnetic Warheads
The issue of electromagnetic weapon lethality is complex. Unlike
the technology base for weapon construction, which has been widely
published in the open literature, lethality related issues have
been published much less frequently.
While the calculation of electromagnetic field strengths achievable
at a given radius for a given device design is a straightforward
task, determining a kill probability for a given class of target
under such conditions is not.
This is for good reasons. The first is that target types are very
diverse in their electromagnetic hardness, or ability to resist
damage. Equipment which has been intentionally shielded and hardened
against electromagnetic attack will withstand orders of magnitude
greater field strengths than standard commercially rated equipment.
Moreover, various manufacturer's implementations of like types of
equipment may vary significantly in hardness due the idiosyncrasies
of specific electrical designs, cabling schemes and chassis/shielding
The second major problem area in determining lethality is that
of coupling efficiency, which is a measure of how much power is
transferred from the field produced by the weapon into the target.
Only power coupled into the target can cause useful damage.
In assessing how power is coupled into targets, two principal
coupling modes are recognised in the literature:
Front Door Coupling occurs typically when power from a electromagnetic
weapon is coupled into an antenna associated with radar or communications
equipment. The antenna subsystem is designed to couple power in
and out of the equipment, and thus provides an efficient path
for the power flow from the electromagnetic weapon to enter the
equipment and cause damage.
Back Door Coupling occurs when the electromagnetic field from
a weapon produces large transient currents (termed spikes, when
produced by a low frequency weapon ) or electrical standing waves
(when produced by a HPM weapon) on fixed electrical wiring and
cables interconnecting equipment, or providing connections to
mains power or the telephone network. Equipment connected to exposed
cables or wiring will experience either high voltage transient
spikes or standing waves which can damage power supplies and communications
interfaces if these are not hardened. Moreover, should the transient
penetrate into the equipment, damage can be done to other devices
A low frequency weapon will couple well into a typical wiring
infrastructure, as most telephone lines, networking cables and power
lines follow streets, building risers and corridors. In most instances
any particular cable run will comprise multiple linear segments
joined at approximately right angles. Whatever the relative orientation
of the weapons field, more than one linear segment of the cable
run is likely to be oriented such that a good coupling efficiency
can be achieved.
It is worth noting at this point the safe operating envelopes
of some typical types of semiconductor devices. Manufacturer's guaranteed
breakdown voltage ratings for Silicon high frequency bipolar transistors,
widely used in communications equipment, typically vary between
15 V and 65 V. Gallium Arsenide Field Effect Transistors are usually
rated at about 10V. High density Dynamic Random Access Memories
(DRAM), an essential part of any computer, are usually rated to
7 V against earth. Generic CMOS logic is rated between 7 V and 15
V, and microprocessors running off 3.3 V or 5 V power supplies are
usually rated very closely to that voltage. Whilst many modern devices
are equipped with additional protection circuits at each pin, to
sink electrostatic discharges, sustained or repeated application
of a high voltage will often defeat these.
Communications interfaces and power supplies must typically meet
electrical safety requirements imposed by regulators. Such interfaces
are usually protected by isolation transformers with ratings from
hundreds of Volts to about 2 to 3 kV.
It is clearly evident that once the defence provided by a transformer,
cable pulse arrestor or shielding is breached, voltages even as
low as 50 V can inflict substantial damage upon computer and communications
equipment. The author has seen a number of equipment items (computers,
consumer electronics) exposed to low frequency high voltage spikes
(near lightning strikes, electrical power transients), and in every
instance the damage was extensive, often requiring replacement of
most semiconductors in the equipment.
HPM weapons operating in the centimetric and millimetric bands
however offer an additional coupling mechanism to Back Door Coupling.
This is the ability to directly couple into equipment through ventilation
holes, gaps between panels and poorly shielded interfaces. Under
these conditions, any aperture into the equipment behaves much like
a slot in a microwave cavity, allowing microwave radiation to directly
excite or enter the cavity. The microwave radiation will form a
spatial standing wave pattern within the equipment. Components situated
within the anti-nodes within the standing wave pattern will be exposed
to potentially high electromagnetic fields.
Because microwave weapons can couple more readily than low frequency
weapons, and can in many instances bypass protection devices designed
to stop low frequency coupling, microwave weapons have the potential
to be significantly more lethal than low frequency weapons.
What research has been done in this area illustrates the difficulty
in producing workable models for predicting equipment vulnerability.
It does however provide a solid basis for shielding strategies and
hardening of equipment.
The diversity of likely target types and the unknown geometrical
layout and electrical characteristics of the wiring and cabling
infrastructure surrounding a target makes the exact prediction of
A general approach for dealing with wiring and cabling related
back door coupling is to determine a known lethal voltage level,
and then use this to find the required field strength to generate
this voltage. Once the field strength is known, the lethal radius
for a given weapon configuration can be calculated.
A trivial example is that of a 10 GW 5 GHz HPM device illuminating
a footprint of 400 to 500 metres diameter, from a distance of several
hundred metres. This will result in field strengths of several kiloVolts
per metre within the device footprint, in turn capable of producing
voltages of hundreds of volts to kiloVolts on exposed wires or cables.
This suggests lethal radii of the order of hundreds of metres, subject
to weapon performance and target set electrical hardness.
Maximising Electromagnetic Bomb Lethality
To maximise the lethality of an electromagnetic bomb it is necessary
to maximise the power coupled into the target set.
The first step in maximising bomb lethality is is to maximise
the peak power and duration of the radiation of the weapon. For
a given bomb size, this is accomplished by using the most powerful
flux compression generator (and Vircator in a HPM bomb) which will
fit the weapon size, and by maximising the efficiency of internal
power transfers in the weapon. Energy which is not emitted is energy
wasted at the expense of lethality.
The second step is to maximise the coupling efficiency into the
target set. A good strategy for dealing with a complex and diverse
target set is to exploit every coupling opportunity available within
the bandwidth of the weapon.
A low frequency bomb built around an FCG will require a large
antenna to provide good coupling of power from the weapon into the
surrounding environment. Whilst weapons built this way are inherently
wide band, as most of the power produced lies in the frequency band
below 1 MHz compact antennas are not an option. One possible scheme
is for a bomb approaching its programmed firing altitude to deploy
five linear antenna elements. These are produced by firing off cable
spools which unwind several hundred metres of cable. Four radial
antenna elements form a "virtual" earth plane around the bomb, while
an axial antenna element is used to radiate the power from the FCG.
The choice of element lengths would need to be carefully matched
to the frequency characteristics of the weapon, to produce the desired
field strength. A high power coupling pulse transformer is used
to match the low impedance FCG output to the much higher impedance
of the antenna, and ensure that the current pulse does not vapourise
the cable prematurely.
Other alternatives are possible. One is to simply guide the bomb
very close to the target, and rely upon the near field produced
by the FCG winding, which is in effect a loop antenna of very small
diameter relative to the wavelength. Whilst coupling efficiency
is inherently poor, the use of a guided bomb would allow the warhead
to be positioned accurately within metres of a target. An area worth
further investigation in this context is the use of low frequency
bombs to damage or destroy magnetic tape libraries, as the near
fields in the vicinity of a flux generator are of the order of magnitude
of the coercivity of most modern magnetic materials.
Microwave bombs have a broader range of coupling modes and given
the small wavelength in comparison with bomb dimensions, can be
readily focussed against targets with a compact antenna assembly.
Assuming that the antenna provides the required weapon footprint,
there are at least two mechanisms which can be employed to further
The first is sweeping the frequency or chirping the Vircator.
This can improve coupling efficiency in comparison with a single
frequency weapon, by enabling the radiation to couple into apertures
and resonances over a range of frequencies. In this fashion, a larger
number of coupling opportunities are exploited.
The second mechanism which can be exploited to improve coupling
is the polarisation of the weapon's emission. If we assume that
the orientations of possible coupling apertures and resonances in
the target set are random in relation to the weapon's antenna orientation,
a linearly polarised emission will only exploit half of the opportunities
available. A circularly polarised emission will exploit all coupling
The practical constraint is that it may be difficult to produce
an efficient high power circularly polarised antenna design which
is compact and performs over a wide band. Some work therefore needs
to be done on tapered helix or conical spiral type antennas capable
of handling high power levels, and a suitable interface to a Vircator
with multiple extraction ports must devised. A possible implementation
is depicted in Fig.5. In this arrangement, power is coupled from
the tube by stubs which directly feed a multi-filar conical helix
antenna. An implementation of this scheme would need to address
the specific requirements of bandwidth, beamwidth, efficiency of
coupling from the tube, while delivering circularly polarised radiation.
Another aspect of electromagnetic bomb lethality is its detonation
altitude, and by varying the detonation altitude, a tradeoff may
be achieved between the size of the lethal footprint and the intensity
of the electromagnetic field in that footprint. This provides the
option of sacrificing weapon coverage to achieve kills against targets
of greater electromagnetic hardness, for a given bomb size (Fig.7,
8). This is not unlike the use of airburst explosive devices.
In summary, lethality is maximised by maximising power output
and the efficiency of energy transfer from the weapon to the target
set. Microwave weapons offer the ability to focus nearly all of
their energy output into the lethal footprint, and offer the ability
to exploit a wider range of coupling modes. Therefore, microwave
bombs are the preferred choice.
Targeting Electromagnetic Bombs
The task of identifying targets for attack with electromagnetic
bombs can be complex. Certain categories of target will be very
easy to identify and engage. Buildings housing government offices
and thus computer equipment, production facilities, military bases
and known radar sites and communications nodes are all targets which
can be readily identified through conventional photographic, satellite,
imaging radar, electronic reconnaissance and humint operations.
These targets are typically geographically fixed and thus may be
attacked providing that the aircraft can penetrate to weapon release
range. With the accuracy inherent in GPS/inertially guided weapons,
the electromagnetic bomb can be programmed to detonate at the optimal
position to inflict a maximum of electrical damage.
Mobile and camouflaged targets which radiate overtly can also
be readily engaged. Mobile and relocatable air defence equipment,
mobile communications nodes and naval vessels are all good examples
of this category of target. While radiating, their positions can
be precisely tracked with suitable Electronic Support Measures (ESM)
and Emitter Locating Systems (ELS) carried either by the launch
platform or a remote surveillance platform. In the latter instance
target coordinates can be continuously datalinked to the launch
platform. As most such targets move relatively slowly, they are
unlikely to escape the footprint of the electromagnetic bomb during
the weapon's flight time.
Mobile or hidden targets which do not overtly radiate may present
a problem, particularly should conventional means of targeting be
employed. A technical solution to this problem does however exist,
for many types of target. This solution is the detection and tracking
of Unintentional Emission (UE). UE has attracted most attention
in the context of TEMPEST surveillance, where transient emanations
leaking out from equipment due poor shielding can be detected and
in many instances demodulated to recover useful intelligence. Termed
Van Eck radiation, such emissions can only be suppressed by rigorous
shielding and emission control techniques, such as are employed
in TEMPEST rated equipment.
Whilst the demodulation of UE can be a technically difficult task
to perform well, in the context of targeting electromagnetic bombs
this problem does not arise. To target such an emitter for attack
requires only the ability to identify the type of emission and thus
target type, and to isolate its position with sufficient accuracy
to deliver the bomb. Because the emissions from computer monitors,
peripherals, processor equipment, switchmode power supplies, electrical
motors, internal combustion engine ignition systems, variable duty
cycle electrical power controllers (thyristor or triac based), superheterodyne
receiver local oscillators and computer networking cables are all
distinct in their frequencies and modulations, a suitable Emitter
Locating System can be designed to detect, identify and track such
sources of emission.
A good precedent for this targeting paradigm exists. During the
SEA (Vietnam) conflict the United States Air Force (USAF) operated
a number of night interdiction gunships which used direction finding
receivers to track the emissions from vehicle ignition systems.
Once a truck was identified and tracked, the gunship would engage
Because UE occurs at relatively low power levels, the use of this
detection method prior to the outbreak of hostilities can be difficult,
as it may be necessary to overfly hostile territory to find signals
of usable intensity. The use of stealthy reconnaissance aircraft
or long range, stealthy Unmanned Aerial Vehicles (UAV) may be required.
The latter also raises the possibility of autonomous electromagnetic
warhead armed expendable UAVs, fitted with appropriate homing receivers.
These would be programmed to loiter in a target area until a suitable
emitter is detected, upon which the UAV would home in and expend
itself against the target.
The Delivery of Conventional Electromagnetic Bombs
As with explosive warheads, electromagnetic warheads will occupy
a volume of physical space and will also have some given mass (weight)
determined by the density of the internal hardware. Like explosive
warheads, electromagnetic warheads may be fitted to a range of delivery
Known existing applications involve fitting an electromagnetic
warhead to a cruise missile airframe. The choice of a cruise missile
airframe will restrict the weight of the weapon to about 340 kg
(750 lb), although some sacrifice in airframe fuel capacity could
see this size increased. A limitation in all such applications is
the need to carry an electrical energy storage device, eg a battery,
to provide the current used to charge the capacitors used to prime
the FCG prior to its discharge. Therefore the available payload
capacity will be split between the electrical storage and the weapon
In wholly autonomous weapons such as cruise missiles, the size
of the priming current source and its battery may well impose important
limitations on weapon capability. Air delivered bombs, which have
a flight time between tens of seconds to minutes, could be built
to exploit the launch aircraft's power systems. In such a bomb design,
the bomb's capacitor bank can be charged by the launch aircraft
enroute to target, and after release a much smaller onboard power
supply could be used to maintain the charge in the priming source
prior to weapon initiation.
An electromagnetic bomb delivered by a conventional aircraft can
offer a much better ratio of electromagnetic device mass to total
bomb mass, as most of the bomb mass can be dedicated to the electromagnetic
device installation itself. It follows therefore, that for a given
technology an electromagnetic bomb of identical mass to a electromagnetic
warhead equipped missile can have a much greater lethality, assuming
equal accuracy of delivery and technologically similar electromagnetic
A missile borne electromagnetic warhead installation will comprise
the electromagnetic device, an electrical energy converter, and
an onboard storage device such as a battery. As the weapon is pumped,
the battery is drained. The electromagnetic device will be detonated
by the missile's onboard fusing system. In a cruise missile, this
will be tied to the navigation system; in an anti-shipping missile
the radar seeker and in an air-to-air missile, the proximity fusing
system. The warhead fraction (ie ratio of total payload (warhead)
mass to launch mass of the weapon) will be between 15% and 30%.
An electromagnetic bomb warhead will comprise an electromagnetic
device, an electrical energy converter and a energy storage device
to pump and sustain the electromagnetic device charge after separation
from the delivery platform. Fusing could be provided by a radar
altimeter fuse to airburst the bomb, a barometric fuse or in GPS/inertially
guided bombs, the navigation system. The warhead fraction could
be as high as 85%, with most of the usable mass occupied by the
electromagnetic device and its supporting hardware.
Due to the potentially large lethal radius of an electromagnetic
device, compared to an explosive device of similar mass, standoff
delivery would be prudent. Whilst this is an inherent characteristic
of weapons such as cruise missiles, potential applications of these
devices to glidebombs, anti-shipping missiles and air-to-air missiles
would dictate fire and forget guidance of the appropriate variety,
to allow the launching aircraft to gain adequate separation of several
miles before warhead detonation.
The recent advent of GPS satellite navigation guidance kits for
conventional bombs and glidebombs has provided the optimal means
for cheaply delivering such weapons. While GPS guided weapons without
differential GPS enhancements may lack the pinpoint accuracy of
laser or television guided munitions, they are still quite accurate
(CEP \(~~ 40 ft) and importantly, cheap, autonomous all weather
The USAF has recently deployed the Northrop GAM (GPS Aided Munition)
on the B-2 bomber, and will by the end of the decade deploy the
GPS/inertially guided GBU-29/30 JDAM (Joint Direct Attack Munition)[MDC95]
and the AGM-154 JSOW (Joint Stand Off Weapon) [PERGLER94] glidebomb.
Other countries are also developing this technology, the Australian
BAeA AGW (Agile Glide Weapon) glidebomb achieving a glide range
of about 140 km (75 nmi) when launched from altitude.
The importance of glidebombs as delivery means for HPM warheads
is threefold. Firstly, the glidebomb can be released from outside
effective radius of target air defences, therefore minimising the
risk to the launch aircraft. Secondly, the large standoff range
means that the aircraft can remain well clear of the bomb's effects.
Finally the bomb's autopilot may be programmed to shape the terminal
trajectory of the weapon, such that a target may be engaged from
the most suitable altitude and aspect.
A major advantage of using electromagnetic bombs is that they
may be delivered by any tactical aircraft with a nav-attack system
capable of delivering GPS guided munitions. As we can expect GPS
guided munitions to be become the standard weapon in use by Western
air forces by the end of this decade, every aircraft capable of
delivering a standard guided munition also becomes a potential delivery
vehicle for a electromagnetic bomb. Should weapon ballistic properties
be identical to the standard weapon, no software changes to the
aircraft would be required.
Because of the simplicity of electromagnetic bombs in comparison
with weapons such as Anti Radiation Missiles (ARM), it is not unreasonable
to expect that these should be both cheaper to manufacture, and
easier to support in the field, thus allowing for more substantial
weapon stocks. In turn this makes saturation attacks a much more
In this context it is worth noting that the USAF's possesion of
the JDAM capable F-117A and B-2A will provide the capability to
deliver E-bombs against arbitrary high value targets with virtual
impunity. The ability of a B-2A to deliver up to sixteen GAM/JDAM
fitted E-bomb warheads with a 20 ft class CEP would allow a small
number of such aircraft to deliver a decisive blow against key strategic,
air defence and theatre targets. A strike and electronic combat
capable derivative of the F-22 would also be a viable delivery platform
for an E-bomb/JDAM. With its superb radius, low signature and supersonic
cruise capability an RFB-22 could attack air defence sites, C3I
sites, airbases and strategic targets with E-bombs, achieving a
significant shock effect. A good case may be argued for the whole
F-22 build to be JDAM/E-bomb capable, as this would allow the USAF
to apply the maximum concentration of force against arbitrary air
and surface targets during the opening phase of an air campaign.
Defence Against Electromagnetic Bombs
The most effective defence against electromagnetic bombs is to
prevent their delivery by destroying the launch platform or delivery
vehicle, as is the case with nuclear weapons. This however may not
always be possible, and therefore systems which can be expected
to suffer exposure to the electromagnetic weapons effects must be
The most effective method is to wholly contain the equipment in
an electrically conductive enclosure, termed a Faraday cage, which
prevents the electromagnetic field from gaining access to the protected
equipment. However, most such equipment must communicate with and
be fed with power from the outside world, and this can provide entry
points via which electrical transients may enter the enclosure and
effect damage. While optical fibres address this requirement for
transferring data in and out, electrical power feeds remain an ongoing
Where an electrically conductive channel must enter the enclosure,
electromagnetic arresting devices must be fitted. A range of devices
exist, however care must be taken in determining their parameters
to ensure that they can deal with the rise time and strength of
electrical transients produced by electromagnetic devices. Reports
from the US indicate that hardening measures attuned to the behaviour
of nuclear EMP bombs do not perform well when dealing with some
conventional microwave electromagnetic device designs.
It is significant that hardening of systems must be carried out
at a system level, as electromagnetic damage to any single element
of a complex system could inhibit the function of the whole system.
Hardening new build equipment and systems will add a substantial
cost burden. Older equipment and systems may be impossible to harden
properly and may require complete replacement. In simple terms,
hardening by design is significantly easier than attempting to harden
An interesting aspect of electrical damage to targets is the possibility
of wounding semiconductor devices thereby causing equipment to suffer
repetitive intermittent faults rather than complete failures. Such
faults would tie down considerable maintenance resources while also
diminishing the confidence of the operators in the equipment's reliability.
Intermittent faults may not be possible to repair economically,
thereby causing equipment in this state to be removed from service
permanently, with considerable loss in maintenance hours during
damage diagnosis. This factor must also be considered when assessing
the hardness of equipment against electromagnetic attack, as partial
or incomplete hardening may in this fashion cause more difficulties
than it would solve. Indeed, shielding which is incomplete may resonate
when excited by radiation and thus contribute to damage inflicted
upon the equipment contained within it.
Other than hardening against attack, facilities which are concealed
should not radiate readily detectable emissions. Where radio frequency
communications must be used, low probability of intercept (ie spread
spectrum) techniques should be employed exclusively to preclude
the use of site emissions for electromagnetic targeting purposes.
Appropriate suppression of UE is also mandatory.
Communications networks for voice, data and services should employ
topologies with sufficient redundancy and failover mechanisms to
allow operation with multiple nodes and links inoperative. This
will deny a user of electromagnetic bombs the option of disabling
large portions if not the whole of the network by taking down one
or more key nodes or links with a single or small number of attacks.
Limitations of Electromagnetic Bombs
The limitations of electromagnetic weapons are determined by weapon
implementation and means of delivery. Weapon implementation will
determine the electromagnetic field strength achievable at a given
radius, and its spectral distribution. Means of delivery will constrain
the accuracy with which the weapon can be positioned in relation
to the intended target. Both constrain lethality.
In the context of targeting military equipment, it must be noted
that thermionic technology (ie vacuum tube equipment) is substantially
more resilient to the electromagnetic weapons effects than solid
state (ie transistor) technology. Therefore a weapon optimised to
destroy solid state computers and receivers may cause little or
no damage to a thermionic technology device, for instance early
1960s Soviet military equipment. Therefore a hard electrical kill
may not be achieved against such targets unless a suitable weapon
This underscores another limitation of electromagnetic weapons,
which is the difficulty in kill assessment. Radiating targets such
as radars or communications equipment may continue to radiate after
an attack even though their receivers and data processing systems
have been damaged or destroyed. This means that equipment which
has been successfully attacked may still appear to operate. Conversely
an opponent may shut down an emitter if attack is imminent and the
absence of emissions means that the success or failure of the attack
may not be immediately apparent.
Assessing whether an attack on a non radiating emitter has
been successful is more problematic. A good case can be made for
developing tools specifically for the purpose of analysing unintended
emissions, not only for targeting purposes, but also for kill assessment.
An important factor in assessing the lethal coverage of an electromagnetic
weapon is atmospheric propagation. While the relationship between
electromagnetic field strength and distance from the weapon is one
of an inverse square law in free space, the decay in lethal effect
with increasing distance within the atmosphere will be greater due
quantum physical absorption effects. This is particularly so at
higher frequencies, and significant absorption peaks due water vapour
and oxygen exist at frequencies above 20 GHz. These will therefore
contain the effect of HPM weapons to shorter radii than are ideally
achievable in the K and L frequency bands.
Means of delivery will limit the lethality of an electromagnetic
bomb by introducing limits to the weapon's size and the accuracy
of its delivery. Should the delivery error be of the order of the
weapon's lethal radius for a given detonation altitude, lethality
will be significantly diminished. This is of particular importance
when assessing the lethality of unguided electromagnetic bombs,
as delivery errors will be more substantial than those experienced
with guided weapons such as GPS guided bombs.
Therefore accuracy of delivery and achievable lethal radius must
be considered against the allowable collateral damage for the chosen
target. Where collateral electrical damage is a consideration, accuracy
of delivery and lethal radius are key parameters. An inaccurately
delivered weapon of large lethal radius may be unusable against
a target should the likely collateral electrical damage be beyond
acceptable limits. This can be a major issue for users constrained
by treaty provisions on collateral damage.
The Proliferation of Electromagnetic Bombs
At the time of writing, the United States and the CIS are the
only two nations with the established technology base and the depth
of specific experience to design weapons based upon this technology.
However, the relative simplicity of the FCG and the Vircator suggests
that any nation with even a 1940s technology base, once in possession
of engineering drawings and specifications for such weapons, could
As an example, the fabrication of an effective FCG can be accomplished
with basic electrical materials, common plastic explosives such
as C-4 or Semtex, and readily available machine tools such as lathes
and suitable mandrels for forming coils. Disregarding the overheads
of design, which do not apply in this context, a two stage FCG could
be fabricated for a cost as low as $1,000-2,000, at Western labour
rates. This cost could be even lower in a Third World or newly industrialised
While the relative simplicity and thus low cost of such weapons
can be considered of benefit to First World nations intending to
build viable war stocks or maintain production in wartime, the possibility
of less developed nations mass producing such weapons is alarming.
The dependence of modern economies upon their information technology
infrastructure makes them highly vulnerable to attack with such
weapons, providing that these can be delivered to their targets.
Of major concern is the vulnerability resulting from increasing
use of communications and data communications schemes based upon
copper cable media. If the copper medium were to be replaced en
masse with optical fibre in order to achieve higher bandwidths,
the communications infrastructure would become significantly more
robust against electromagnetic attack as a result. However, the
current trend is to exploit existing distribution media such as
cable TV and telephone wiring to provide multiple Megabit/s data
distribution (eg cable modems, ADSL/HDSL/VDSL) to premises. Moreover,
the gradual replacement of coaxial Ethernet networking with 10-Base-T
twisted pair equipment has further increased the vulnerability of
wiring systems inside buildings. It is not unreasonable to assume
that the data and services communications infrastructure in the
West will remain a "soft" electromagnetic target in the forseeable
At this time no counter-proliferation regimes exist. Should treaties
be agreed to limit the proliferation of electromagnetic weapons,
they would be virtually impossible to enforce given the common availability
of suitable materials and tools.
With the former CIS suffering significant economic difficulties,
the possibility of CIS designed microwave and pulse power technology
leaking out to Third World nations or terrorist organisations should
not be discounted. The threat of electromagnetic bomb proliferation
is very real.
A Doctrine for the Use of Conventional Electromagnetic
A fundamental tenet of IW is that complex organisational systems
such as governments, industries and military forces cannot function
without the flow of information through their structures. Information
flows within these structures in several directions, under typical
conditions of function. A trivial model for this function would
see commands and directives flowing outward from a central decisionmaking
element, with information about the state of the system flowing
in the opposite direction. Real systems are substantially more complex