This locomotive was built by the American Locomotive Company in 1943 as part of an order of 105 Challengers for the Union Pacific. #3985 was in front-line service until 1957. She was retired and placed in storage in 1962. In 1975, she was moved to the Cheyenne Depot to be put on public display. A group of Union Pacific employees worked to restore the locomotive to running condition in 1981. In 1990, she was converted from coal to burn a heavy bunker oil. When #3985 is not out pulling tourist trains, she is housed in Cheyenne, Wyoming. #3985 is the largest and most powerful steam locomotive in operation in the world at this time.