Arthur H. Fetter, the General Mechanical Engineer, had been designing locomotives for the Union Pacific since 1918, and had been responsible for the development of its 4-8-2 "Mountain" and 4-10-2 "Overland" locomotives as well as many other innovations and improvements to UP motive power. Fetter suggested a high speed articulated locomotive to reduce the reciprocating weight of a compound and to increase the 50 mph speed limit of the railroad's most powerful locomotives, the rigid wheeled 4-12-2s.
Fetter had a long standing working arrangement with the American Locomotive Company and he often collaborated with ALCO's engineers on locomotive designs. For the new more powerful locomotive he and the ALCO engineers started with the 4-12-2. They decided that the leading four wheel truck would be needed for better side control. They split the six sets of drivers into two groups of three and replaced the two 27" outside cylinders and the one 31" middle cylinder with four 22" x 32" cylinders. Two inches were added to the diameter of the boiler and the pressure was raised from 220 psi to 255 psi. The firebox was enlarged and they added a four wheel trailing truck to carry its added weight.
The first 4-6-6-4, UP number 3900, was received from ALCO at Council Bluffs on August 25, 1936, and after a brief ceremony it headed west pulling a refrigerator train.
During a meeting in 1936, in which Otto Jabelmann, the VP of Research, and William Jeffers, the Executive VP of the Union Pacific System listened to J. W. Burnett, the General Superintendent of Motive Power and Machinery, propose a test run for the new locomotive. Burnett had decided to operate it unassisted from Ogden to Wahsatch and then run fast over to Green River before turning back to Ogden with another train. Burnett said "that is a challenge for any locomotive" and Jeffers replied "it certainly is...let's call them "Challengers". After the meeting Jeffers sent a memo to the Advertising Department in which he said he wanted the name "Challenger" used in all press releases about the new locomotive.
The Union Pacific Railroad would buy a total of 105 "Challengers" and eight other railroads would use the other 147 of the total 252 that were built. The Baldwin Locomotive Works built 27 of the 4-6-6-4s. The American Locomotive Company built the rest.
Information for this introduction to Challengers provided by Richard Duley.
|Railroad Line||Quantity, Builder|
|Clinchfield||12 ALCO, 6 from D&RGW|
|Delaware & Hudson||40 ALCO|
|Denver & Rio Grande Western||6 ALCO, 15 Baldwin|
|Great Northern||2 from SP&S|
|Northern Pacific||47 ALCO|
|Spokane, Portland & Seattle||8 ALCO|
|Union Pacific||105 ALCO|
|Western Maryland||12 Baldwin|
|Western Pacific||7 ALCO|
|No.||Class||F.M. Whyte||Gauge||Railroad Line||Location||Status||Builder Info||Notes|