The Pennsylvania Railroad
's K4s 4-6-2
"Pacific" (425 built 1914–1928, PRR Altoona, Baldwin
) was their premier passenger-hauling steam locomotive
from 1914 through the end of steam on the PRR in 1957.
Attempts were made to replace the K4s, including the K5
and the T1 duplex locomotive
, but none was really successful, and the K4s hauled the vast majority of express passenger trains until replaced by diesel locomotives
. The K4s was not powerful enough for the weight of trains it was often called upon to haul from the mid 1930s onward, and so they were often double or even triple headed. This was effective, but wasteful in that several crews were needed. The PRR did have the extra locomotives, because many had been displaced by electrification
. Since the PRR had often referred to itself as the Standard Railroad of the World, the K4 has sometimes been referred to as the Standard Passenger Locomotive of the World.
It is recognized as the State Steam Locomotive of Pennsylvania.
The K4s was designed under the supervision of PRR Chief of Motive Power J.T. Wallis
, assisted by Chief Mechanical Engineer Alfred W. Gibbs
and Mechanical Engineer Axel Vogt
, as one of a pair of classes with the L1s 2-8-2
"Mikado", sharing a boiler and other features. A fair amount of inspiration came from the large experimental K29s
Pacific built in 1911 by the American Locomotive Company
. Also influential was Gibbs' design for the successful E6 4-4-2
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