I was stationed at Minot Air Force Base in Minot, North Dakota. While on post one night, about 2300 hours, a sentry noticed something strange in the sky while scanning with his thermal imager. The sentry called myself and my partner over to look and confirm what he was seeing. He described what appeared to be a star moving in the sky high above base. To the naked eye, nothing appeared out of the ordinary. To me this ruled out a satellite because they can be seen without any kind of equipment. The moment I looked through the thermal imager I could make out what did indeed appear to be a star or satellite, however, it was moving all around the sky. Not fast, but slow. Just a solid, white light. I looked again with my own eyes and could not spot it, but with the thermal imager it was very prominent. I watched it for several seconds when to my amazement, it split into two objects. But that wasn't it, soon one of them split again! One object had turned into four objects in a couple minutes time. I had no possible idea what they could be as they were obviously not falling stars or anything of that nature. The four objects moved all around the sky above us, not fast but slow. They were high up and appeared as small, white spots of light. Not being able to see them with the naked eye, but to see them so prominently with the thermal imager, told us they were giving off a great amount of heat. While we were watching the objects I caught movement low on the horizon. I looked down and saw two more flying low across the flight line, moving west to east. They appeared large, and with the thermal imager they were giving off an intense amount of heat. They went out of sight so my partner and I jumped in the vehicle and headed towards the flight line to see if we could get a better look. We got into a better position, got out and started scanning. Before long, we noticed one of the spots of light moving back our way. Coming from the east right towards us. I was watching with one eye in the thermal imager and my other eye open to the sky. As the object moved closer, it got brighter and brighter in the thermal imager. It had to be giving off an incredible amount of heat. As I followed it, it came into the glow of the lights from base. My partner and I could not believe our eyes. It was within about 100 yards, moving smoothly and silently from east to west. It was a large, pyramid shaped craft. The base was towards the ground with the point straight up to the sky. Right off I figured it was roughly two stories high. Each side was maybe 25-30 feet across. It did not spin, it moved perfectly level, not quite over the top of us. It had no features of any kind. I could not make out doors, windows, or lights. I could not see any seams or rivets of any kind. It was completely smooth and featureless. I could not tell what color it was, but the lights from base glow orange and the craft appeared a dull brown, leading me to believe the craft may have been gray in color, or possibly somewhat reflective. What amazed me most was it was absolutely silent. Being as close as it was, we should have heard any kind of engine noise. There wasn't even a rush of air as it moved. It was so smooth and impossibly quiet. We felt no vibrations or anything else as it went by. It made no sudden maneuvers of any kind. It moved off to the west in a straight line and disappeared. We continued to watch objects high in the sky until midnight, 2400. Just as suddenly as they appeared, they disappeared. We watched the rest of the night and saw nothing. We did not lose track of any time. I kept track as we watched. My partner and I were bewildered. I had seen a UFO once when I was younger. It had been quick and shocking, and I had always wished to see one again. I was so excited and yet quite puzzled as to what I saw. My partner was pretty shaken up. The next night, while I was on post, I was watching the sky intently when I noticed an airplane high above base. Judging from the positioning of the blinking lights, it was rather large. It circled high above base for quite some time before moving off and disappearing. Even for an Air Force Base, this did not appear normal to me. For several nights after, we kept our eyes open to the sky but never saw anything else. I had kept a detailed log with descriptions and drawings, but unfortunately it was lost when Minot flooded in 2011. I constantly replay the event in my mind and can see the UFO plain as day. I will never forget it.