No railroad was better equipped to shoulder the heavy burden of wartime traffic thanks to the three types of Union Pacific steam locomotives that constituted its front line of defense: the 4-6-6-4 Challenger, arguably the most successful simple articulated ever made; the 4-8-8-4 Big Boy, which easily wore the mantle “world’s largest steam locomotive”; and the 800-class 4-8-4s, among the finest of all Northerns.
UP already had long experience with the Challenger, introduced in 1936 to answer the railroad’s need for horsepower rather than just pulling power. Railroading’s drag-freight era was over; speed was of the essence. The UP’s reigning giant, the 4-12-2, would give way to the 4-6-6-4, with its more flexible wheelbase, lighter-weight rods, and ample boiler. The railroad already had 85 Challengers on the roster in 1944 when it went back to Alco for 20 more, this time for engines with slightly smaller cylinders and a shorter firebox but a boost in boiler pressure from 255 to 280 psi. They were the last of UP’s Challengers.
By 1944, the railroad world had already run out of superlatives for UP’s Big Boy 4-8-8-4s, 20 of which were built by Alco in 1941. They starred in UP publicity and movie-theater newsreels, and why not? Extrapolated from the Challengers, the 4000s operated at the practical limit of boiler pressure, 300 psi. They produced energy in a firebox 8 feet wide and nearly 20 feet long, including the combustion chamber. All this power was delivered to two sets of eight-coupled 68-inch drivers, putting 135,375 pounds of tractive force in the hands of the engineer. The last 5 of the giants arrived in 1944. The Big Boys more than fulfilled their mission, hauling unprecedented volumes of freight east out of Ogden, Utah.
And that brings us to the thoroughbreds of the UP fleet, the 45 members of the FEF (“four eight four”) class. These huge Northerns were comparable to any on American rails — including Santa Fe’s 2900s. The first order of 20 FEF-1s arrived from Alco in 1937, boasting 77-inch drivers, a boiler pressure of 260 psi, and 63,611 pounds of tractive force. They were upsized in subsequent orders, including 15 FEF-2s in 1939 and 10 FEF-3s in 1944, all with 80-inch drivers and 300 psi of boiler pressure but only a slight increase in tractive force. Designed in the era of standard heavyweight cars, they ended up looking fine on the point of streamliners — and troop trains and freights. The last and most famous among them, 844, was never retired and continues to reside in UP’s heritage program.
