The SDP45 is a six-axle, C-C, diesel-electric locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois. It was a passenger-hauling version of the SD45 on a stretched locomotive frame with an extended, squared-off long hood at the rear, aft of the radiators, giving space for a steam generator for passenger train heating. This steam generator placement followed the pattern set by the SDP35 and SDP40. Original owners The Southern Pacific Railroad ordered their ten on May 9, 1966, with the units being placed in service between May 24 and July 26, 1967, initially on the City of San Francisco between Oakland and Ogden, and eventually used system-wide. As built, each unit carried of fuel and of steam generator water in a partitioned underframe tank. The steam generator was a Vapor Model OK-4740. SP's units had Pyle National Gyralights on the leading end, came with Nathan P-3 horns, and cost $317,156 each (SP's straight SD45's from the same period cost $290,788 each). Ordered with 62:15 gearing with the overspeed set at , the gearing was changed to 60:17 (overspeed at ) during 1968–1969. All except 3201 and 3207 would eventually be re-geared back to 62:15 once they entered commuter service. After Amtrak took over long-distance routes in 1971, various units were leased to Amtrak for West Coast service (primarily on the Coast Starlight) until Amtrak purchased their SDP40F locomotives, while the rest were used in freight service and on Company specials. Beginning in 1973 the SDP45s were used for commuter service on the San Francisco Peninsula Commute, replacing the Fairbanks-Morse Train Masters. SP's commuter service was demanding work and the locomotives required electrical modification to meet those demands. A "Passenger Start" switch was installed inside the cab electrical cabinet; in the "COMM" position the units were held in Parallel, in the "FRT/PASS" position normal transition was made. They stayed on the commute route (often working in freight service on weekends) until 1985 when Caltrain equipment arrived, and they were placed into freight service until their retirement, initially working out of Roseville, then in local and hauler service in the Los Angeles Basin. All were retired between 1986 (3208) and 1990 (3204) and sold for scrap. The Great Northern Railway purchased eight SDP45s in 1967 to replace F-units on the Empire Builder. Normally paired back-to-back, they were also used singly leading F-units. These joined six smaller SDP40 locomotives ordered in