I was working the midnight shift on a gov. installation. Security work. My partner and I were on a routine patrol of the perimeter fence line of the installation. We had stopped to observe a northern section of the fence line. I noticed a dim light in the distance, that seemed to be above the ground level and tree line. So we stayed in the vehicle and observed the light configuration as it grew nearer to our position. It was a dark moonless night, and you couldn't see your hand in front of your face. The one light that we first observed had gotten larger, and it was soon apparent that the craft had a glowing globe on each of its corners. As the craft continued to approach, the air seemed to get muggy and hard to breath. It was like a dead air situation. The craft just kept getting larger and larger, as it approached our position. It seemed like a long time had passed when it finally reached the fence line where we were. The size of that thing was huge, it was at least 300 to 350 ft. in length and at least 125 to 150 ft. wide on the tail end of its triangle shape. The top of the craft was not dome shaped, but it looked like it was a raised structure with portals along its sides, like the port holes in the side of a sailing ship. They were dimly lit and in a neat row close to the mid line of the craft. The bottom of the craft was like a giant convex mirror. Every thing that it passed over was reflected in it like it was high noon on a bright sunny day. I could even see my own reflection along with my partner and the patrol truck in it. And there was no light reflected back from its surface to the surrounding area. The craft was moving at a snails pace of about 5 to 7 miles an hour. If I would have climbed into the bed of the patrol truck, I could have reached up and touched the craft with my hands. The craft drifted over the tree line to our south of our position and we lost sight of it. Since the craft was moving at such a slow rate, we got back into the truck and moved for a better vantage point to see it egress the area. But when we had moved only about 100 yards to the next clearing, or vantage point the craft had vanished. When I reported this incident to my boss, I was told not to repeat it to anyone. He told me that he had seen it to. And hinted to me that if I knew what was good for my job, I didn't see what I saw. And if I where ask by any one about the situation, I was to tell them that all I had seen was a low flying air craft with engine trouble. When I told him that I knew just what I saw, I also told him that I was a licensed pilot, certified by the FAA, And that was no aircraft that was from this earth, he told me to just keep my mouth shut and get out of his office. I can supply additional information in the form of a hand drawn sketch but I'll have to send it snail mail. I have no way to upload it into my computer. The other witness to this sighting, to this day, still refuses to acknowledge any truth to this event for fear of public ridicule.