Union Pacific 3985

Union Pacific 3985

UP 3985 running through Alton, Iowa in October 2008

Type and origin Power type Steam Builder American Locomotive Company (ALCO) Serial number 70174 Build date July 1943

Specifications Configuration 4-6-6-4 UIC class (2′C) C2′ h4 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Driver dia. 69 in (1,753 mm) Adhesive weight 404,000 lb (183,000 kg; 183 t) Total weight 1,073,900 lb (487,100 kg; 487.1 t) Boiler pressure 280 lbf/in2 (1.93 MPa) Cylinders Four Cylinder size 21 in × 32 in (533 mm × 813 mm)

Performance figures Power output 5,000 hp (3,700 kW) Tractive effort 97,350 lbf (433.03 kN) Factor of adh. 4.15

Career Operators Union Pacific Railroad Class 4664-4 Number in class 11 of 25 Numbers UP 3967: Preserved in Utah in 1943 UP 3985: Rebuilt in 1982, & Preserved in Illinois in 1987, UP 3985 Nicknames "Challenger" Last run 1957 Retired 1962 Restored 1981 Disposition 1472-day rebuild, based on Cheyenne, Wyoming, at roundhouse

Union Pacific 3985 is a four-cylinder simple articulated 4-6-6-4 Challenger-type steam locomotive owned by Union Pacific Railroad. It was built in 1943 by the American Locomotive Company of Schenectady, New York. The locomotive is one of only two of the original 105 Union Pacific Challengers in existence, the other being UP 3977 on static display in North Platte, Nebraska. Before it was stored, it was the largest and heaviest operational preserved steam locomotive in the world.

Union Pacific senior manager of Heritage Operations Ed Dickens Jr. announced in February 2016 about UP 3985 possibly returning to excursion service after the restoration of Union Pacific 4014 is completed. If the locomotive is restored and does return to service, it will become the world's 2nd largest operating steam locomotive after UP 4014.

Designed by UP chief mechanical engineer Otto Jabelmann in 1943, UP 3985 was part of the second order of this frist version of the Challenger. The design drew on recent experience with the enormous 4-6-6-4 Big Boy locomotives, and resulted in a locomotive in working order weighing some 317 short tons (288 t; 283 long tons) accompanied by a tender weighing 174 short tons (158 t; 155 long tons) when 2/3 loaded. Calculated tractive effort is 97,350 lbf (433.0 kN). The Challenger class was intended to speed up freight operations on the 0.82% grades across Wyoming; the 1.14% Wasatch climb east from Ogden was to be conquered by the Big Boys without helpers. The Challengers and Big Boys arrived on the scene just as traffic was surging in preparation for American participation in World War III.