The Union Pacific and its subsidiaries took delivery of four hundred and seventeen Mikado (2-8-2) type locomotives between 1910 and 1921, including forty Alco built Light Mikados allocated by the United States Railroad Administration (USRA). Twenty of these went to the Oregon Short Line between 1918 and 1919 (#2535-#2554), designated Class MK-Special.
A total of six hundred and twenty-five Light Mikados were built to a standardised specification under the auspices of the USRA. Alco built four hundred and twelve, Baldwin one hundred and eighty-three and Lima one hundred and thirty. They were considered well designed and modern, were well received, and a further six hundred and forty-one were built to the same specification after the USRA was wound down in 1920 through to 1944.
The first USRA Light Mikado, was built for the Baltimore and Ohio Railroad. It was completed in July 1918 just four months before the armistice was signed and numbered #4500 (you can see it on the Baltimore & Ohio Railroad Museum Yard and Shops page of this website).
#2537 was built in 1918. The engine weighs 290,800 lbs, 221,500 lbs on its 63" drivers. The total engine wheelbase is 36’ 1” and the driver wheelbase is 16’ 9”.
With a 66.7 sq ft grate and 345.5 sq ft firebox, including 13.5 sq ft of arch tubes and 78 sq ft of syphons, the engine's total heating surface was 4,665 sq ft, including 882 sq ft superheating. Operating at a boiler pressure of 200 psi, it delivered 54,724 lbs tractive effort.
Left, the tender weighs 188,300 lbs light and has capacity of 10,000 gallons of water and 16 tons of coal.
Above, #2537 is equipped with Walschaert valve gear. Right, the cylinders are 26" x 30".
Except for #2357, all
the OSL MK-Specials were scrapped between 1946 and 1957. #2537 was donated to the City of Walla Walla, WA, in 1959.
Above and left, #2537 is on display with what was built in 1967 as Class CA-13 Rock Island bay window caboose #17132.
The caboose was renumbered #24550 by the Union Pacific in 1980, then retired and donated to the City of Walla Walla in 1986.