Human warfighters are not the sole users of battlefield camouflage, of course. Tanks, infantry fighting vehicles, trucks, Humvees, command tents, and so on typically use paint or fabric schemes, netting, and other covers in an attempt to blend into the background, reduce IR signatures, and escape detection, primarily from aerial reconnaissance – manned or unmanned aircraft – and satellites.

Because military vehicles quickly become covered in dirt, mud, or sand, paint schemes alone provide only marginal protection. Efforts also must be made to reduce reflectivity, so the vehicle does not “shine” or glitter in sunlight, a problem typically increased when the vehicle is wet. Netting, which is continuously being improved in design and materials, has been the best solution to date, although natural cover – from hiding beneath trees or in the shell of a building to covering the vehicle with leaves, branches, or even rubble – remains common.

The addition of IR suppressive materials provides added protection against both air and ground detection, but all such measures still leave the item being covered vulnerable to radar. As a result, the definition of camouflage has now been expanded through the introduction of stealth technologies, such as radar-defeating shapes and materials and electronic disruption of enemy detection and weapons guidance systems. But defeating electronic detection is a far greater challenge than fooling the human eye and brain.

Some of the most advanced, full-enclosure concepts of the old Future Warrior program – often compared to the attire of Imperial Troopers in the Star Wars movies – would have accomplished that by creating a self-contained environment providing heating and cooling, as required, to the wearer while exhibiting only ambient heat signatures externally.

Night vision goggles and weapon scopes, for example, have enabled military operations to continue at night, which historically provided cover to both forces on the move and those seeking rest and resupply. Traditional camouflage is useless against systems that use the heat produced by the human body and military equipment to locate potential targets. While IR-masking materials, from netting that also incorporates camouflage designs and colors for daytime concealment to thermal blankets and other materials, can help protect equipment – from computers to tanks – it is not enough.

That also applies to humans, leading to research into how to block the detection of body heat through special materials for clothing and packs. The problem is doing so without “cooking” the wearer.

Some of the most advanced, full-enclosure concepts of the old Future Warrior program – often compared to the attire of Imperial Troopers in the Star Wars movies – would have accomplished that by creating a self-contained environment providing heating and cooling, as required, to the wearer while exhibiting only ambient heat signatures externally. Such combat suits also might incorporate digital capabilities to change patterns and colors to match the warfighter’s immediate surroundings, in true chameleon fashion, and block advanced detection systems based on anything from heartbeat to breathing to electrical activity in the brain.

At an even greater extreme, some have theorized incorporation of “invisibility” technology into such suits.

The work of Duke University professor David R. Smith, especially during his tour as a program manager at the Defense Advanced Research Projects Agency (DARPA), has been widely publicized, most spectacularly in a cable TV program claiming he had developed an “invisibility cloak.” Currently director of the Center for Metamaterial and Integrated Plasmonics at Duke, Smith tried to set the record straight in a paper entitled “The Science Fact and Fiction of Invisibility.”

While acknowledging that many real science breakthroughs and research efforts have been inspired by science fiction – from authors such as H.G. Wells and Isaac Asimov to the Star Trek TV shows and Star Wars movies – he also noted science fiction can escape the rules of physics and known technology through the simple tactic of making up their own – such as the Heisenberg Compensator, a never-explained device that overcomes one of several major obstacles to allow transporters to work. Real scientists, however, are bound by the laws of physics and current or near-term technology.

However, while theoretically possible, based on the bending of light near massive gravitational sources, such as black holes, creating a portable device carried aboard a ship and being able to turn it on and off, in his words, leaves it “firmly the domain of science fiction.”

DARPA is unique among government agencies in not only being allowed, but encouraged, to pursue concepts and technologies that may not come into regular use for decades – if then. Those have included the Internet, aircraft stealth, unmanned air and ground vehicles, robots, directed energy, artificial intelligence, virtual reality, precision guidance, hypersonic flight, bionic prosthetics, controlling mechanical devices by thought, and flying cars.

During his time with DARPA, Smith led a research team investigating, among other things, invisibility. He has continued that work at Duke, with research into the electromagnetic properties of artificially structured materials – metamaterials – and the theoretical potential to design a material that would render objects invisible.

He also sees some “glimmer of reality” in the cloaking technology used by Star Trek’s Romulans to make their starships not only undetectable by sensors, but also invisible to the naked eye. However, while theoretically possible, based on the bending of light near massive gravitational sources, such as black holes, creating a portable device carried aboard a ship and being able to turn it on and off, in his words, leaves it “firmly the domain of science fiction.”

Perhaps surprisingly, Smith sees far greater potential for real-world invisibility in a science – rather than magic – based version of Harry Potter’s invisibility cloak. By using the right materials, he wrote, it might be possible to bend light around the cloak – which would create a sphere surrounding the object to be concealed – without requiring a black hole’s gravity well.

“The capabilities and limitations of cloaking will continue to be sorted out in the coming months and years, but there are some issues that are clear from the outset,” Smith wrote. “The cloak is a complicated structure. Not just complicated, but one that requires materials that are not known to exist. This appears to be one difficulty we can surmount by the use of artificial micro- and nano-structures that can substitute for the lack of conventional materials having the right properties. And while the cloaking structures are complex as materials go, they are nevertheless easily fabricated using available technologies.

“There is an inherent limitation in bandwidth. [Light] rays that would normally impinge on the cloaked sphere must instead be swept around the sphere, essentially traversing a longer distance than they would have had they passed directly through a volume of space. For all the rays to arrive in step after swirling around the sphere, they must travel faster than the speed of light in vacuum while in the cloak. This isn’t quite as bad as it sounds … it is possible for electromagnetic waves to exceed the speed of light within a material, but only at a particular wavelength (or, equivalently, frequency). Thus … our cloak can be designed to work optimally at a targeted wavelength or bandwidth, but its performance will degrade sharply away from the optimal bandwidth.”

“The advantage of invisibility comes about when your adversary has no idea you’re there. That is, invisibility is probably best thought of as being a really good form of camouflage – it doesn’t have to be perfect to work.”

If those problems can be overcome, Smith added one element of good news for potential users – “a cloak needn’t accomplish complete invisibility to be potentially useful.”

“Being invisible is only of fleeting value, at best, if your adversary knows you are there. The advantage of invisibility comes about when your adversary has no idea you’re there. That is, invisibility is probably best thought of as being a really good form of camouflage – it doesn’t have to be perfect to work,” he wrote, then cited another unexpected fictional character to demonstrate. “In perhaps one of the most realistic portrayals of invisibility, the alien in the movie Predator possesses a cloaking device that renders it nearly invisible.

“When cloaked, the predator is mostly transparent, but there is a noticeable distortion of the transmitted light that just vaguely outlines the shape of the predator. As depicted in the movie, it is difficult to perceive the presence of the alien unless you know it’s there and it’s in motion. Otherwise, the imperfect cloaking does a pretty good job of keeping the alien well hidden. Although the underlying fictional technology is not described in the movie, the cloaking effect appears to be related to the alien’s armor, which would make it more akin to the material cloak that we think might be possible.”

Contrary to some media speculation following release of his report, Smith said it is extremely unlikely any form of invisibility will be achieved within the next decade.

“The physics of cloaking is sound and cloaks may be fabricated using the artificial materials that have been introduced over the past several years. But there are serious and seemingly unavoidable limitations on cloaking that will impair the performance of any structure we can currently envision making,” he said.

“So when we ourselves project a demonstration will be possible, what we have in mind initially is a very specific sort of structure that will most likely be useable [but not necessarily useful] at very long wavelengths in the electromagnetic spectrum – radio frequencies, for example, where wavelengths are on the order of many centimeters to meters. It may not be quite as exciting as making objects visibly disappear, but it will be an important step. How much further might we go beyond this initial demonstration is an open question, but given the tremendous interest in the area, we can say for certain that the scientific community will do its best.”

“The physics of cloaking is sound and cloaks may be fabricated using the artificial materials that have been introduced over the past several years. But there are serious and seemingly unavoidable limitations on cloaking that will impair the performance of any structure we can currently envision making,” he said.

Overall, then, the future of camouflage for land forces – indeed, all military and paramilitary units – appears on the edge of the first significant change since Ice Age hunters covered themselves with mud and leaves, first to trick game animals, later other humans during combat.

“One last point to consider is that the entire design paradigm that leads to the cloak – starting by transforming space and then determining the equivalent electromagnetic material – represents a new approach to optics,” Smith concluded. “Just five years ago, this idea of transformed optics might have been abandoned because the resulting material requirements would have been considered impractical.

“With the advent of metamaterials, that conclusion has now changed and we can envision entirely new classes of optical devices, invisibility cloaks being just one example. So, while we have been inspired by the invisibility of fictional worlds, perhaps the discoveries that might follow from transformation optics will in turn have an impact in fictional worlds – as well as in the actual world.”

This article was first published in Defense: Land Forces Edition, Fall 2010.