War is hell. William T. Sherman, the Civil War general, made this statement back in 1880, but it's just as true today. The current conflict in Iraq, now almost three years old, is confronting American soldiers with horrors that we on the home front can only guess at. Recently, however, I got a high-tech glimpse of what the grunts in Iraq must be going through. During a visit to the U.S. Naval Research Laboratory (NRL) in Washington, D.C., I immersed myself in several virtual-reality training systems that can simulate urban combat with uncanny realism by allowing users to walk, march and run inside an electronic battlefield.

The Office of Naval Research is developing these systems as part of a six-year, $40-million program called Virtual Technologies and Environments (VIRTE). Much of the work focuses on the needs of the Marine Corps, which is engaged in some of the bloodiest fighting in Iraq. My first stop at NRL was a small windowless room containing the VirtuSphere, a nine-foot-high hollow ball made of sturdy perforated plastic. The VirtuSphere rests on 26 wheels rising from a stationary platform; the wheels allow the sphere to rotate in place like a giant trackball, turning in any direction. Next to the sphere was its Russian co¿inventor, Nurakhmed Latypov, whose company--also named Virtu¿Sphere--is working with VIRTE to incorporate this contraption into a training system.

Latypov gave me a demonstration. He opened the VirtuSphere's hatch, stepped inside and began running full-tilt like a hamster in an exercise wheel. As the sphere turns, two tracking devices fire ultrasound beams at it from below and measure the Doppler shift of the echoes to determine the speed and direction of its spin. This information goes into a virtual-reality program running on a nearby computer, which calculates what the path of the user would be if he or she were traveling through a simulated landscape instead of scrambling inside the VirtuSphere. The user wears virtual-reality goggles that display the landscape, which advances and recedes as the person moves about. (The system transmits the signal wirelessly to the head-mounted display through the VirtuSphere's perforated shell.) The goggles have accelerometers and magnetometers to detect changes in the orientation of the user's head--if the individual turns left, right, up or down, his or her view of the virtual world pivots accordingly.

The marines are interested in the VirtuSphere because real-life combat training facilities are expensive and often impractical, especially at temporary bases overseas. The Virtu¿Sphere, in contrast, can be taken to the front lines or onboard ships and assembled in a few hours. Conducting maneuvers in the device, however, takes a little practice. When I entered the VirtuSphere, I had trouble keeping my balance. Although it was relatively easy to start walking and change direction, it was harder to slow down and stop. At one point I took a step backward and went tumbling. Still, after a few minutes I felt confident enough to don the head-mounted display and begin my virtual trek.

The first program I tried was a three-dimensional rendering of a proposed sports center to be built in Moscow. (Latypov had previously used the program to assist Moscow's bid for the 2012 Olympics.) In fits and starts, my feet turned the VirtuSphere, propelling me up the stairways and down the corridors of this weirdly barren virtual building. I came to a long hallway lined with identical doors that opened automatically when I approached. "I hope this isn't the women's room," I said as I walked through one of the doorways, but the room was empty.

I finally reached an indoor swimming pool, where I encountered a surprise: animated monsters that looked vaguely like bugs and robots. I was supposed to shoot the monsters using a handheld controller, but I still felt a little unsteady. Perhaps sensing my ineptitude, the program generated a second shooter who appeared on my display as a flickering soldier. As I tried to get out of the line of fire, I heard a shot. I spun around and saw a splatter of blood on the floor. Although the program's graphics were no more sophisticated than those of an ordinary computer game, the simulated violence seemed much more intense and confusing because I couldn't see everything at once. By the time I ended the program and stepped out of the sphere, I was sweating copiously.