The AC-9 was one of two Southern Pacific Railroad's

articulated An articulated vehicle is a vehicle which has a permanent or semi-permanent pivot joint in its construction, allowing it to turn more sharply. There are many kinds, from heavy equipment to buses, trams and trains. Steam locomotives were sometim ...

steam locomotive classes that ran

smokebox A smokebox is one of the major basic parts of a steam locomotive exhaust system. Smoke and hot gases pass from the firebox through tubes where they pass heat to the surrounding water in the boiler. The smoke then enters the smokebox, and is e ...

forward after 1920. Twelve AC-9 class locomotives were built by

Lima Lima ( ; ), originally founded as Ciudad de Los Reyes (City of The Kings) is the capital and the largest city of Peru. It is located in the valleys of the Chillón, Rímac and Lurín Rivers, in the desert zone of the central coastal part of ...

in 1939 and were Southern Pacific's largest and heaviest steam engines, partly a consequence of low quality coal these engines were designed to burn. The AC-9s were partially streamlined (the only articulated steam engines to be so equipped), having "skyline casings" inspired by Lima's GS series of

4-8-4 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of four leading wheels on two axles, eight powered and coupled driving wheels on four axles and four trailing wheels on two axles. The type wa ...

's, also made for Southern Pacific, and were equipped with coal tenders, unlike the cab forwards. The

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

was

2-8-8-4 A 2-8-8-4 steam locomotive, under the Whyte notation, has two leading wheels, two sets of eight driving wheels, and a four-wheel trailing truck. The type was generally named the ''Yellowstone'', a name given it by the first owner, the Northern Pa ...

, which was nicknamed "Yellowstone". Between 1939 and 1953, all the twelve AC-9 engines were in service between

Tucumcari, New Mexico Tucumcari (; ) is a city in and the county seat of Quay County, New Mexico, United States. The population was 5,278 at the 2020 census. Tucumcari was founded in 1901, two years before Quay County was established. History In 1901, the Chicago, ...

El Paso, Texas El Paso (; "the pass") is a city in and the county seat, seat of El Paso County, Texas, El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the United States Census Bureau, U.S. Census Bureau w ...

, and

Tucson, Arizona , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...

, where they mainly pulled freight trains and occasionally also passenger trains such as the ''

Golden State Limited The ''Golden State'' was a named passenger train between Chicago and Los Angeles from 1902–1968 on the Chicago, Rock Island and Pacific Railroad (“Rock Island”) and the Southern Pacific Company (SP) and predecessors. It was named for Cal ...

''. Between May and August 1950, they were converted to burn oil instead of coal, and in spring 1953 eleven of them moved to Southern Pacific's Modoc line between Sparks, Nevada, and

Alturas, California Alturas (Spanish for "Heights"; Achumawi: ''Kasalektawi'') is a city and the county seat of Modoc County, California. Located in the Shasta Cascade region of Northern California, the city had a population of 2,715 at the 2020 census. Altur ...

, where they worked in freight service from 1953 until retirement in early summer 1956. None were preserved. All were scrapped in 1956 with none survived to preservation.

External links

The Yellowstone Type Locomotive

{{DEFAULTSORT:Southern Pacific class AC-09 Steam locomotives of the United States AC-09 2-8-8-4 locomotives Lima locomotives Simple articulated locomotives Railway locomotives introduced in 1939 Freight locomotives Scrapped locomotives Standard gauge locomotives of the United States