The only operating example in the world of the largest steam locomotive ever built thundered her way, in May 2019, from Union Pacific’s Steam Shop in Cheyenne, Wyo., to Ogden, Utah, to take part in ceremonies marking the 150th anniversary of the Golden Spike, which completed the nation’s first transcontinental railroad.
She’s “Big Boy” 4014, built in 1941 by the American Locomotive Co. to UP specifications for hauling heavy trains over the Wasatch Mountains between Ogden and Green River, Wyo., on a 1.14% ruling grade.
Beginning in the late 1930s, a UP design team led by Mechanical Department Research & Mechanical Standards Vice President Otto Jabelmann, working with ALCO, re-evaluated the railroad’s 4-6-6-4 Challenger locomotives. They enlarged the Challenger’s firebox to 235 x 96 inches (157 square feet), increased boiler pressure to 300 psi, added four driving wheels and reduced driving wheel diameter from 69 to 68 inches. The resulting single-expansion, articulated, 975.75-ton (with tender, in working order) 4-8-8-4 featured an axle loading of 67,800 pounds (33.9 tons), and a maximum starting tractive effort of 135,375 pounds with a 4.0 factor of adhesion.
ALCO manufactured 25 Big Boys for UP, 20 in 1941 and five in 1944. They saw service until their fires were dropped for the last time in 1961. Eight survived; UP re-acquired 4014 in 2013 from the RailGiants Museum in Pomona, Calif., and meticulously restored her to operating condition.
The nine-page Railway Age article of Oct. 4, 1941, pp. 519-526 and 528, downloadable from the link below, describes the Big Boy in full technical detail, listing all component suppliers, some of which are still in business. Also available for download are the elevation and cross-section technical drawings, in a single graphic assembled from pp. 522-523.
This iconic locomotive, at this writing on a western tour on UP lines, joins her siblings, 4-6-6-4 Challenger 3985 and 4-8-4 Northern 844, in UP’s steam program.
We salute Union Pacific, its Steam Team and all the suppliers who returned 4014 to glory.