Union Pacifics Northern-type locomotives were built by ALCOs Schenectady Works in three classes between August 1937 and December 1944. The first class, designated FEF-1 (for Four-Eight-Four), consisted of locomotives 800819. Equipped with 77-inch drivers and a 300-psi boiler, these locomotives impressed UP enough to order 15 additional engines between August and October 1939. These locomotives, numbered 820834, featured 80-inch drivers and larger 14-wheel centipede tenders with a 23,500-gallon capacity and were designated FEF-2.

In December 1944, ten additional 4-8-4 locomotives were delivered, numbered 835844. These engines featured low-backpressure double stacks and were designated FEF-3. All three classes developed an impressive 63,800 pounds of tractive effort.

This production run features several historically accurate variations of Union Pacific No. 844 from its early excursion career. These include the locomotive