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Little History:

  The AC-9 was one of two Southern Pacific Railroad's articulated steam locomotive classes that ran smokebox forward after 1920. Twelve AC-9 class locomotives were built by Lima 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's, also made for Southern Pacific, and were equipped with coal tenders, unlike the cab forwards. The wheel arrangement was 2-8-8-4, which was nicknamed ''Yellowstone''.


Original Design.