Cheyenne, WyomingOctober 1955

On the evening of October 16, 1955, two men hunting near Cheyenne, Wyoming heard a loud whining sound that they believed came from a strange aircraft. One of the men said he looked up and saw a dark object outlined against the stars, roughly the size of a car and 50 to 60 feet overhead. He described it as traveling west at tremendous speed. The other witness heard the sound for about 45 seconds but did not see the object. Both men later reported the sighting to the Civil Aeronautics Administration tower at Cheyenne airport.

The Air Force investigation that followed found serious problems with the account. The first witness initially claimed he had seen the object, but later retracted that statement and admitted he had only heard the noise. He also needed thick eyeglasses but was not wearing them at the time of the sighting. His description of what he saw kept changing. The second witness showed a tendency toward exaggeration and professed to be a "saucer enthusiast," influencing his account of events. More importantly, investigators interviewed many neighbors and officials in the area who reported hearing or seeing nothing unusual that evening, despite the witnesses' claims that the sound was comparable to four to six jet aircraft at full throttle.

The breakthrough came when investigators learned that Union Pacific locomotive number 987 had passed one and a half miles south of the sighting location at almost exactly the time the men reported. The locomotive consisted of three units containing six diesel-electric engines running at full power to climb the mountains west of Cheyenne. Investigators concluded that sound from the locomotive, carried by south-southeast winds across the cool evening air and amplified by the local topography, would have produced the whining noise the men described. The second witness's mention of the sound resembling "turbine" engines matched the characteristics of diesel-electric engines. An officer at Warren Air Force Base reported that trains passing in that area sometimes sounded odd and loud.

The investigating officer concluded that no actual object was present. The sound the men heard was from the passing train, he wrote, and their overactive imaginations had filled in the visual details. The approving Air Force officer concurred with this assessment. The case was officially marked unidentified, though the file contains the investigative conclusion that a terrestrial explanation existed. This case file comprises 10 pages held by the National Archives.