Power type Steam Total produced 105 UIC class (2′C)C2′ h4 | Build date 1936–1944 Configuration 4-6-6-4 | |
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Builder American Locomotive Company (ALCO) | ||
The Union Pacific Challengers were a type of simple articulated 4-6-6-4 steam locomotive built by American Locomotive Company for the Union Pacific Railroad. 105 of these locomotives were built between 1936 and 1943. The Challengers were nearly 122 ft (37 m) long and weighed 314 tons (284,800 kg). They operated over most of the Union Pacific system, primarily in freight service, but a few were assigned to passenger trains operating through mountain territory to California and Oregon. The locomotives were built specifically for Union Pacific and much of the experience gained later went into the design of the "Big Boy".
Contents
The name "Challenger" was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading pilot truck, which helps guide the locomotive into curves, two sets of six driving wheels, and finally four trailing wheels, which support the rear of the engine and its massive firebox. Each set of six driving wheels is driven by two steam cylinders. In essence, the result is two engines under one boiler. The Union Pacific Railroad sponsored development of this type to meet the need for higher speeds in main-line service. Historically, articulated locomotives had been limited to slow speeds by factors inherent in their design. The technical breakthroughs achieved with the Challenger enabled the carrier to develop the Big Boy with the same speed expectations. Speeds in excess of 60 M.P.H., while unheard-of on other railroads using articulated steam locomotives, became commonplace on the Union Pacific.
Construction
The 105 were divided into five orders, which can be put into two groups: the first two orders of "light" Challengers, and the final three of "heavy" Challengers.
As part of Union Pacific's fourth order in 1943, ALCO built 31 locomotives for Union Pacific using the same specifications. However, the War Production Board diverted 6 locomotives after completion to the Denver & Rio Grande Western Railroad via a lease through the War Department's Defense Plant Corporation. Locomotives 3900-3905 formed the Rio Grande's Class L-97. These were later sold to Clinchfield Railroad in 1947, becoming 670-675.
Preservation
Two examples survive today: Union Pacific 3985, which remains in operating condition and is used for excursion services by Union Pacific, and Union Pacific 3977, which is on static display on Cody Park at North Platte, NE. None of the original Challengers that were built for Union Pacific were preserved.
As of November 2016, 3985 is down indefinitely for repairs, placed second in line behind Union Pacific 4014 in the restoration order. 4014 is scheduled to be completed in 2019. Once 4014 is restored, crews will start work on 3985 for a 2-3 year overhaul. 3985 could be back in steam by 2021 (2022 at the latest).