Union Pacific 9000 Class

The Union Pacific 9000 Class was a class of 88 three-cylinder 4-12-2 steam locomotives built by the American Locomotive Company between 1926 and 1930. It was the only class ever built with a 4-12-2 wheel arrangement, nicknamed the Union Pacific type after its sole operator, and the largest rigid frame locomotive ever made, about 102 feet long. The locomotives used the Gresley conjugated valve gear licensed from the London and North Eastern Railway, but the inside cylinder made maintenance expensive and the long rigid wheelbase needed gentle curves. Only the prototype, number 9000, survives, preserved at the Railway and Locomotive Historical Society museum at Pomona, California.