An SD9 is a 6-axle road switcher diesel locomotive built by General Motors Electro-Motive Division between January 1954 and June 1959. An EMD 567C 16-cylinder engine generated 1,750 horsepower (1.30 MW). This model is, externally, similar to its predecessor, the SD7, but this model, internally, features the improved and much more maintainable 567C engine. The principal spotting feature are the classification lights on the ends of the locomotive, above the number board. The SD9's classification lights are on a small pod, canted outward. The last phase of construction had a carbody similar to the SD18 and SD24, and used two 48-inch (1,219 mm) cooling fans instead of four 36-inch (914 mm) cooling fans.
Four hundred and seventy-one SD9s were built for American railroads and 44 for export.
Many SD9s both high and short-hood can still be found in service today on shortline railroads and industrial operators. And while most Class 1 roads stopped using these locomotives by the 1970s and 1980s, some remain in rebuilt form on some major Class I railroads, as switcher locomotives..
Nickel Plate Road 349 is preserved at the Mad River & Nickel Plate Railroad Museum. It was retired as Norfolk Southern #52, and was donated to the museum in December 2010. It has been restored to its Norfolk & Western appearance.