Union Pacific Big Boy

The Union Pacific Big Boy is a class of articulated steam locomotives built by the American Locomotive Company in Schenectady, New York for the Union Pacific Railroad, twenty in 1941 and five more in 1944, to a design led by Otto Jabelmann of Union Pacific's Research and Mechanical Standards section. They used a 4-8-8-4 wheel arrangement found on no other locomotive class and were built to haul long freight trains over the mountain grades between Ogden, Utah and Green River, Wyoming, sustaining 60 miles per hour once past the grades where earlier locomotives had needed helper engines. Revenue service ended in July 1959 as diesel power took over; eight Big Boys survive in museums, and No. 4014 was restored to operating condition in 2019, when it was recognized as the largest, heaviest and most powerful operating steam locomotive in the world.