EMD SD7
An SD7 is a 6-axle diesel locomotivebuilt by General Motors Electro-Motive Division between May 1951 and November 1953. It had an EMD 567B 16-cylinder engine producing for its six traction motors. 188 were built for United States railroads. This was the first model in EMD's SD "(Special Duty)" series of locomotives, a lengthened B-B GP7 with a C-C truck arrangement. The two extra axles and traction motors are useful in heavy, low speed freight service. EMD continues to produce SD series locomotives to this day. Many SD7s both high and short-hood  can still be found in service today on shortline railroads and industrial operators, although 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.. Design and Production. The SD7 was conceived as a modification of the GP7 with two additional powered axles, one for each truck. Providing two more axles served two purposes: it gave the locomotive more tractive effort compared to the 4 axle GP7, and distributed the locomotive's weight more evenly. EMD produced its first examples of the SD7 in  May 1951, using the 567B engine. Starting in August 1953 a total of 26 SD7s were produced which used either the 567BC engine or the 567C engine. SD7's were originally set up to run long hood forward, usually noted by the letter "F" painted adjacent to the top step of the long hood boarding steps. Many were later changed or upgraded to run short hood forward as is today's Association of American Railroads standard. EMD ended production in November 1953, and began producing the SD7's successor, the SD9, in January 1954.