Like the Pontiac GTO, the SD45 was a mid-60s General Motors muscle car. Stuffed under its brick-like hood was the largest diesel motor made up to that time, a turbo-charged, 20-cylinder, 3600 hp, Electro-Motive Division model 645E. The Great Northern took delivery of the first SD45 in May of 1966 and promptly painted the nickname "Hustle Muscle" on its flanks. The name said it all: the SD45 was heavy freight power, intended for long trains and high speeds. And it had the muscular looks to match, with flared radiators capping a long body that filled every inch of its frame - as opposed to its baby brother, the SD40, which had an open "porch" at each end of the engine.
Unfortunately, the 20-cylinder motor turned out to have a major flaw: a tendency to break its own crankshaft. Even so, a large number of Class 1 railroads rostered the engine, with 1,260 units sold between 1966 and 1971. The Santa Fe, Burlington Northern, Pennsy, and Southern Pacific each owned more than 100 of the heavy freighters. Looking at the order quantities, one can see that the SD45 marked the beginning of a large-scale shift toward six-axle freight engines on American railroads. Before the late '60s, adding a third axle to a truck was mainly an expedient to spread out an engine's weight for service on lighter rail, particularly branch lines. But with the SD45 and its contemporaries, railroads began favoring the six-axle engine as a way to get more power on the rails for heavier mainline trains. Despite the initial crankshaft problems, many SD45s served their original owners for decades, as well as successor railroads like Conrail and the BNSF, and later went on to new lives at smaller, secondary roads.