The year was 1975 and I was stationed at the Lima missile launch faucility outside of Sturgis SD/ Vail, South Dakota and Bear Butte South Dakota. Bear Butte has long been a religious spot for Native Americans. I was a Security Police Airman with the Air Force. My Partner and I were in-route to a missile silo just west of Bear Butte. We were 1 mile west of Bear Butte when we saw a cigar shaped UFO with pulsating lights approaching the top of Bear Butte from the north. The UFO stopped and hovered above Bear Butte for about 15 minutes and the slowly moved off toward the south, started to accelerate faster and then with-in seconds the UFO was gone. No sound, no vapor trail, no sonic boom, just gone with-in seconds...