Military researchers are working on perfecting high-power microwave weapons that can invisibly smash enemy electronics.
Such "directed-energy", or e-weapons, exploit the increasing reliance on electrical and computer systems in almost every aspect of the military.
For that reason the researchers have also been investigating ways to shield their own military systems against enemy attack and even "friendly fire".
The weapons involve generating an extremely short-lived but extremely powerful energy pulse.
Scientists got the idea years ago during high-altitude atomic bomb tests, when they discovered that the blast incidentally produced an electromagnetic pulse which damaged electrical installations over a wide area.
The pulse can wreak havoc without needing physically to destroy anything or harm people.
In a paper detailing the possible ways of using this in a weapon, Australian defence analyst Carlo Kopp wrote: "As a punitive weapon electromagnetic devices are attractive for dealing with belligerent governments.
"Substantial economic, military and political damage may be inflicted with a modest commitment of resources by their users, and without politically damaging loss of life."
High power microwave (HPM) devices involve accelerating an electron beam against a mesh to produce microwave oscillations that can be tuned to release very high power.
In theory, this makes an ideal weapon to use against "hardened" targets such as command bunkers buried underground and protected by masses of reinforced concrete.
These still have to be connected to the outside world - by antennas, cables, air ducts or simple weaknesses in their design which can let in the microwave emissions.
Such weapons could also cover a wider area and knock out in one hit a target that might involve several conventional bombs - such as the various elements of a dispersed, mobile anti-aircraft missile system.
And they can be defensive as well as offensive - they might be mounted on, say, a slow-moving transport aircraft and triggered by an approaching enemy missile.
In the arsenal?
Actual weapon development is largely secret.
US Air Force Colonel Eileen Walling wrote in a research paper three years ago: "Several high power microwave technologies have matured to the point where they are now ready for the transition from engineering and manufacturing development to deployment as operational weapons."
Prior to doing that study Col Walling was director of the air force's HPM programme.
The main research in the United States has been done at the Air Force Research Laboratory's directed energy directorate at Kirtland Air Force Base, New Mexico.
The lab has been awarding contracts to a number of companies to investigate "the lethality of high power microwave (HPM) devices on target systems and the susceptibility/vulnerability of US systems to HPM threats" - to be done by 2005.
Some reports have suggested Britain and the United States now have weapons they could use, most probably in expendable cruise missiles or unmanned drone aircraft.
Dr Malcolm Davis of the Centre for Defence Studies at King's College, London, says the Americans do have an e-weapon that can be used in either a conventional bomb or in a cruise missile.
But both use a high explosive to trigger the energy pulse so can be used only once.
The advantage of a non-explosive type would be that a cruise missile or other unmanned aircraft could fly over a region selecting and irradiating targets with electromagnetic energy - in effect, sweeping the area of electronic capability.
"But I'm not aware that the Americans have perfected any electrically-driven e-bomb technology," he said.
"They have gone down the conventional explosive path because that's quicker and easier to do."
Electrically-powered versions need a very high voltage to generate the microwave output.
Researchers say the problem is not only generating that but controlling it and the associated heat that is produced.
But Dr Davis says the Russians have done a lot of work on such weapons and he has seen a photo of an electrically-driven, shoulder-held microwave weapon - resembling a portable SAM anti-aircraft missile launcher.
It was claimed this could knock down an aircraft up to eight kilometres away.
These claims could be exaggerated, he said - but there was no reason technically why you could not generate a pulse of electromagnetic energy in a particular direction.
As long ago as 1998, a Swedish newspaper reported that its country's military had bought and tested a Russian HPM bomb.
The briefcase-sized device was said to emit short, high-energy pulses reaching 10 gigawatts - equivalent to the output from 10 nuclear reactors.
The German company Rheinmetall Weapons and Munitions has also been researching e-weapons for years and has test versions.
It is reported to be collaborating with Russian institutions in developing an HPM generator that could be fitted into a 155mm artillery shell.
The head of US defence company Raytheon Electronic System's directed energy programmes has predicted that there will be HPM weapons within five years.
A thorough study of the subject recently published by American think-tank the Lexington Institute concludes that such weapons will revolutionise warfare - but not just yet.
"Within the next few years, the first weapons systems built with directed-energy as their kill mechanism will be deployed," it says.
Because they do not hurt people or buildings, e-bombs also hold political advantages.
But all developed countries rely increasingly on sophisticated electronics for communications and control in everyday business, including in their health services.
These are just as vulnerable to e-bombs as military systems - perhaps more so, because they are less likely to have been shielded by design.
"There is a doubt about how much you can use e-weapons, given that people don't want to destroy the computers that run hospitals," said Andrew Brookes, an air specialist at the International Institute for Strategic Studies in London.
"If you've got a power station that supplies an air defence system and a hospital and a school and an old people's home, then strictly speaking it's illegal to attack it because it's a 'dual use' capability."
According to the Wall Street Journal, American defence officials "are leaning against using the e-bomb" in Iraq.
It says they are concerned it could alienate ordinary people and raise significantly the cost of rebuilding the country after a war.