In the 1930s, with freight traffic increasing, the Union Pacific
Railroad had to use combinations of its 2-8-8-0 and 2-10-2 locomotives
to get trains over the rugged grades of the Wahsatch Mountains. To stay
competitive, a more powerful locomotive was needed to speed up the
railroad and to reduce the rising cost of helpers and extra trains. The
UP simply needed a locomotive that could climb the Wahsatch faster.
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
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.