Union Pacific #481 was built in 1902 as #1902 by Burnham, Williams & Co., in Philadelphia, PA, later part of Baldwin. It is one of an order for twenty Consolidation (2-8-0) type locomotives built as Vauclain compounds (#1901-#1920 renumbered #480-#499 in 1915).

As built, the 1901s had 15½x 30 high pressure and26x 30 low pressure cylinders. However, by the turn of the century, many US railroads were turning away from compounds and were converting those they owned to single-expansion locomotives. So, between 1910 and 1918, the 1901s were progressively simplified with 21x 30 cylinders, #437 in March 1910.

The 1901s were based on the UP's 1640 Vauclaincompounds (you can see one of these on the UP 1640 #437 page of this website) but heavier, 192,670 lbs, 171,870 lbs on its 57" drivers, with boiler tubes lengthened by a foot and grates increased from 33.9 sq ft to 47 sq ft. With a 191.2 sq ft firebox and total heating surface of 2,584 sq ft, they operated at a boiler pressure of 200 psi, delivering 31,719 lbs tractive effort.