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Unfair Advantage

Today’s stealth technology is close to making every warrior’s ultimate goal of being invisible to the enemy a reality. Using plasma clouds, radioactive paints, light-bending cloth and deadly-silent power plants, the prospect of war could turn into a decidedly one-sided proposition.

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Barricaded behind the rubble of a shattered village, heavily armed fighters watch as enemy troops pick their way down a distant hillside. It is daytime and the glaring sun can easily play tricks on even the most experienced eyes, but the defenders watch in bewilderment as one by one, the approaching soldiers reach up to their helmets, flip a switch and seem to vanish from sight. Without the slightest warning of any sound, there are suddenly a half dozen helicopters, bristling with weapons, hovering above the encampment like a swarm of deadly insects, soundless and fading in and out of sight behind shimmering waves of heat.

Off balance, unsure where to shoot first, one of the better-hidden fighters takes aim at a still-visible foot soldier. The instant his bullet leaves its barrel, a cluster of geo- metrically arrayed microphones on an approaching vehicle triangulates the shock wave and delivers 3D co- ordinates to a soldier's aiming aid. One shot, threat eliminated.

Sounds far-fetched, but the world's major military powers aren't just dreaming about such systems.

Take Michael Callahan of the Pen- tagon's Defense Advanced Research Projects Agency. He is tasked with making the futuristic scenario hap- pen today for the US military. "It is my goal to provide our men and women with an unfair advantage over the enemy," he says.

Up in the Air
While military technology co-opted the term "stealth" 40 years ago, the first large-scale attempt to hide armies and weapons goes back to World War II, with the introduction of patterned camouflage uniforms.

"Stealth," as weapons expert Da- vid Hambling puts it, "comes down to not being spotted by whatever is most dangerous to you."

This is as easy as sticking grass in your helmet for infantry soldiers, but WWII aircraft engineers grap- pled with ways to minimise airframe silhouettes against the daytime sky.

At first they tried painting the underbelly of the airplanes white, or pale blue, to match the sky. They soon realised, however, it was the shadow - not the colour - that made the dark dot in the sky. To get rid of the incriminating shadow, engineers attached fluorescent lights under the fuselage and wings that pilots could dim or brighten to match the time of day. It wasn't perfect, but gave pilots some virtual invisibility.

The quest to make planes invis- ible received an unexpected boost when US space programme scien- tists from NASA noticed that early spacecraft went dead to radar and radio waves upon re-entering the atmosphere. This occurs because the friction heating on re-entry creates

a plasma "bubble" around the craft, making it vanish from radar screens.

Called plasma aerodynamics, the concept seems right out of an episode of "Star Trek," but several inventors say they have a way to cre- ate "cloaking devices" for real.

One suggestion involves an on- board particle accelerator that zaps the atmosphere immediately in front of the aircraft, laying down "a carpet of invisibility" to fly into. Another method advocates us- ing an on-board super-conductor magnetic coil to engulf the craft in a radar-absorbing plasma cloud. A third suggestion involves painting warplanes with radioisotopes that would ionise the surrounding atmo- sphere, creating a plasma sheath.

The beauty of flying your airplane in a plasma sheath is that it also sig- nificantly reduces drag, by as much as 3 percent. The one drawback of painting a fighter, bomber or recon- naissance plane with radioactive isotopes is that they will glow in the dark. There is speculation that some of the glowing in the night skies over the notorious "area 51" in the US state of Nevada, widely speculated as being caused by UFOs, might instead have been the result of the US Air Force's top-secret experi- ments using radioactive paint on U-2 spy planes.

Other stealth approaches involve using high-tech materials that could either scatter incoming radar waves, or even switch their wavelengths, thus confusing the trackers by turn- ing the aircraft's radar signature into random noise.

Lost at Sea
The Swedish Navy leads the way to invisibility on the high seas with its corvette-class Visby warship. Made from the same ultra-hard, carbon- fibre material used in Formula One racing cars, the Visby is light and quick and uses less fuel than more conventional ships in its class.