A tribute to the Union Pacific 4-6-6-4 Challenger locomotive, the 3985 Union Pacific 3985 is a four-cylinder articulated 4-6-6-4 "Challenger"-type steam locomotive built in July 1943 by the American Locomotive Company (ALCO) of Schenectady, New York, for the Union Pacific Railroad. No. 3985 is one of only two Challengers still in existence and the only one to have operated in excursion service. No. 3985 operated in revenue service until 1957. It was then stored in the roundhouse in Cheyenne, Wyo