The Union Pacific Railroad has hosted an excursion program since 1960. The fleet includes two historic steam locomotives and four historic diesel locomotives, accompanied by a fleet of historic passenger cars. Included in the fleet of steam locomotives are Union Pacific 4014, the largest operating steam locomotive in the world, and Union Pacific 844, the only steam locomotive never retired by a North American Class I railroad. Also included are Union Pacific 6936, the only operating example of the longest single-unit diesel locomotive ever built and Union Pacific 949, 951, and 963B, a trio of historic streamlined locomotives. There was also a third steam locomotive: Union Pacific 3985, which operated in excursion service from 1981 to 2010. It was retired from excursion service in January 2020 as a result of its poor condition, and currently remains stored in Cheyenne.