In the 1960s, railroads were looking to replace aging EMD E-units and Alco PAs for passenger service. EMD responded by adding a steam generator compartment to the long hood end of their SD45. This required a longer frame and resulted in the creation of the SDP45. Three railroads originally purchased SDP45s: Southern Pacific, Great Northern, and Erie Lackawanna.
After EL merged into Conrail in 1976, the SDP45s were renumbered as CR 6667 through 6699 and operated for a time in patched EL paint. By the early 1980s, they were all painted into Conrail blue. Conrail mixed the SDP45s with other types of power and used them on a variety of trains. Conrail #6670 resides at the Virginia Museum of Transportation in Roanoke in faded Conrail blue. It was extensively measured and photographed in the development process of our model.