An SD9 is a 6-axle 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 cooling fans instead of four 36-inch cooling fans.
Four hundred and seventy-one SD9s were built for American railroads and 44 for export.