They needed a higher gear ratio for faster running, the graduated-release feature on the air brakes, and type F tightlock couplers to keep equipment together in the event of a derailment.

Earlier passenger diesels, like EMD E8, ALCO PA, FM Erie-built and Baldwin Sharknose locomotives, were streamlined cab units designed for visual appeal and the appearance of speed.

Great Northern Railway (GN) purchased the first six SDP40s in 1966, to replace older E-units on their Western Star and smaller regional trains.

Options included Vapor OK-4740 steam generators, water-transfer capability between units, 59:18 gearing for a top speed of 83 mph (134 km/h), and Type-F couplers.

One SDP40, former GN 323, was temporarily renumbered BN 1976 and painted in red, white and blue for the United States Bicentennial in 1976.

In 2023, the museum repainted the locomotive into the Great Northern's simplified orange and green color paint scheme.