From 1926 until 1930 these locomotives were built by ALCO to pull freight on Union Pacific's lines, a total of 88 were built, at the time these locomotives were the largest rigid wheelbase until the Soviet Union's AA20. From 1953 and 1956, all of these locomotives got retired. Only 1 is around today, Union Pacific No. 9000, the locomotive that was the prototype for its class. It sits at the RailGiants Train Museum at the Fairplex in Pomona California (The same museum that had Big Boy 4014).
