Union Pacific Challenger
UP 3985 running through Alton, Iowa in October 2008
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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 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".
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.
| Class | Quantity | Manufacturer | Serial Nos. | Year | UP No. | Notes |
|---|---|---|---|---|---|---|
| CSA-1 | 15 | American Locomotive Company | 68745–68759 | 1936 | 3900–3914 | Converted to oil fuel in 1941–43; renumbered 3800–3814 in 1944 |
| CSA-2 | 25 | American Locomotive Company | 68924–68948 | 1937 | 3915–3939 | Converted to oil fuel; renumbered 3815–3839 in 1944 |
| 4664-3 | 20 | American Locomotive Company | 69760–69779 | 1942 | 3950–3969 | |
| 4664-4 | 31 | American Locomotive Company | 70158–70162 70169–70182 70678–70683 |
1943 | 3975–3999 | 31 built but only 25 delivered to UP (see below); 3975–3984 converted to oil fuel in 1945; renumbered 3708–3717 in 1952. 3985 in excursion service since 1981. |
| 4664-5 | 20 | American Locomotive Company | 72792–72811 | 1944 | 3930–3949 | 3930/31/32/34/37/38/43/44 converted to oil fuel in 1952 and renumbered 3700–3707. |
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.[1] These were later sold to Clinchfield Railroad in 1947, becoming 670-675.
Two examples survive today: Union Pacific 3985, used for excursion services by Union Pacific and Union Pacific 3977, on static display in North Platte, NE, at Lua error in package.lua at line 80: module 'strict' not found..
External links
- Union Pacific Steam Shop Information on locomotives and excursion schedules.
- UP 3985 Challenger, Steam Locomotive - photos and additional information
- Union Pacific locomotive classes Information on the Challenger and other Union Pacific locomotives
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
