This event occurred in either April or May of 2000 during a military training excercise. I was nearing the end of my fourth and final year of service as a Tank Crewman in the US Army.I was member of a three man tank crew setting up a "screenline" for the first day of a three day defensive mission. We were part of the OpFor or Opposition Forces that play the role of enemy nations and train other army units every month at Fort Irwin, aka NTC (National Training Center).The purpose of a "screenline" is to have minimal forces (typically three or four vehicles) several kilometers in front of the main force to identify and destroy incoming scouts in the days prior to the main battle. Our tank was to be the farthest forward (east) vehicle in this formation. (see attached map for our position in association of other friendly troop formations).Due to mechanical difficulties (engine replacement) we were stuck in maintainance area (see circle near hill on map) until nearly midnight on the first night. Typically, only one or two scouts will try to penetrate the area at this time. As we finally began to roll east just after midnight, we had to move extremely slow as there was no moonlight and our night vision had to rely on starlight for magnification purposes. The driver has one set of night vision goggles, and the tank commander "Mario" had the other pair. Both myself and the tank commander were standing out the open hatches on top of the tank to help guide the driver forward to our position.About two kilometers into our trip (see first tick mark on our path), I noticed a fairly bright light well ahead of us along the horizon (due EAST). Assuming it was just a bright star, or even a planet I kept it to myself for several minutes as we continued to trudge along at only a couple of mile per hour. As I continued to observe (with the naked eye), the object appeared to slowly be rising from the horizon, as if coming towards us, yet still at a great distance... A few minutes later (see second tick mark), I tapped the tank commander who had the night vision goggles and pointed to the object. He too noticed and both of us began to study the light as it slowly appeared to approach us. Several minutes later, we realized the object was going to be fairly close as it passed by the right side (south) of us. Without telling the driver what was going on (he was a young Private, and we didn't want to look like weirdo's) we instructed him to stop the tank and shut down the engine so we could listen. In the absolute silence of the desert in the early AM, we were unable to hear any sound whatsoever as the object continued to approach. We passed the night vision goggles back & fourth in complete disbelief (and a bit of fear I may add) as the object passed within a few hundred yards of our vehicle. It was only about 30-40 feet off the ground, disk shapped, and through the night vision goggles, you could see a beam circulating beneath the object shining at the ground as it went by.Knowing that there weren't supposed to be any aircraft in the area and seeing that we couldn't identify what we saw, we hesitated to break radio silence for sake of not being taken seriously.However a few minutes later several other units farther back in the formation reported "blue-air" (code name for blue forces aircraft). But, quickly they realized it wasn't a helicopter or airplane. At this time, object was no longer in our field of view, but other units reported loosing sight of object. Nobody indicated seeing it shoot off or anything... it just seemed to vanish. ??Neither tank commander or myself were able to sleep that night. We didn't even move the tank after that point. We simply parked out in the open (on tank trail) and kept our eyes peeled until sunrise. Nothing else was seen.There was lots of talk about it at refuelling/breakfast the next morning, but nobody ever figured out what it was, or could have been. Only thing like it I have ever seen.As for the object itself... As I meantioned, it appeared disk shapped, yet it was very very dark out and whatever light we had seen in the distance that was so bright was no longer visible as it closed on us. I don't remember seeing it turn off, but as it got closer, we could only see it through night vision via the beam coming out the bottom. Absolutely SILENT! Based on the rotating light beam, the object had to be at least 20-30 feet wide, but may have been larger. It passed BETWEEN us and the mountain range we call the South Wall which wasn't more than a kilometer and a half away. This was absolutely not something in the sky per say. It was very low. You could see the light beam hitting the ground beneath it which is why I say it was only 200-300 meters from us. Beam may have been infrared since it couldn't be seen with naked eye.