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.
During the merger of Northern Pacific and Great Northern in 1970, the newly formed Burlington Northern assigned GN SDP45s passenger locomotive numbers 9856 through 9863. To protect them from being taken by Amtrak, BN swapped them with F-units. The SDP45s operated for a few more years with their passenger numbers in patched Big Sky Blue and were gradually repainted Cascade Green and black. In April 1974, they were renumbered as freight units 6592 through 6599. As BN units, they remained assigned to Havre, MT until they were retired between 1984 and 1987.