The VirtuSphere is not the only device that allows users to walk inside a virtual world. Because the goal of VIRTE is to develop and evaluate a mix of technologies, an NRL group led by Jim Templeman is working on a system called Gaiter that extrapolates the path of a user in a completely different way. To enter Gaiter, I strapped on a head-mounted display and a flak jacket, as well as forearm and shin guards. All these accessories, plus a model rifle, were tagged with retroreflectors, which can reflect a beam of radiation back to its source regardless of the angle of incidence. Then I was tethered to a harness dangling from the ceiling.

Surrounding me were 10 high-speed cameras that emitted beams of infrared light and captured the reflections. By tracking the motion of my shin guards, the Gaiter system measured my gait--the length and rate of my steps--as I walked in place, lifting my feet up and down. This measurement determined how quickly I moved in the virtual world; if I stepped high and fast, I could zoom across the simulated landscape. I was immersed in a different program now, a reproduction of an actual urban-combat training site at Fort Benning, Ga. I took a virtual stroll past several blocky, brightly colored buildings. When I pointed my rifle or extended my arms, I could see their animated duplicates on the display. I could even knock down simulated chairs or tables in my path.

The major drawback of these systems is their expense. The VirtuSphere, for example, costs between $50,000 and $100,000. (The company hopes to sell an entertainment version to arcades for $20,000.) Cheaper, simpler platforms may suffice for virtual exercises involving large numbers of marines. NRL neuroscientist Roy Stripling is developing a system, informally called Pod 1, that has no complex mechanism for incorporating locomotion--you just press a switch on the rifle's barrel to move back and forth in the virtual world--yet it provides a very lifelike simulation by accurately tracking the twists and turns of the user's torso, head and rifle, which are all marked by red LEDs and monitored by an array of cameras.

Using this system to navigate the Fort Benning program, I managed to enter one of the blocky buildings, climb the stairs to the second floor and stumble into a firefight with the enemy, a squad of computer-generated thugs. In real life I would've been cut to pieces, but the program was set to God mode, making me impervious to their bullets. I closed in on my opponents and shot them point-blank. But when I tried to leave the building, I couldn't find the stairway in the maze of dark rooms now littered with virtual corpses. I was just about to panic when K. C. Pflu¿ger, a marine reservist and independent contractor, said, "Don't worry, I'll get you." He slipped on a pair of goggles and entered the simulation; moments later his avatar--a grunt in camouflage--appeared on my display and led me downstairs.

By this point I was suffering from simulation sickness, an awful nausea induced by too much virtual reality. The NRL researchers had told me that the experience would give me an appreciation for the rigors of combat, and they were right: I felt a small slice of the fear and a fair amount of the exhaustion. But most of all, I was repelled. Even a virtual war can look ugly and futile. No matter how many simulated opponents you kill, they keep on coming, one after another, an inexhaustible enemy, and the program doesn't end until you take the goggles off.

This article was originally published with the title My Virtual War.

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