The Milwaukee Road used a total of three different locomotives to pull the consist between Chicago and Olympia, WA in the early 50s - two electrics (used on electrified portions of the journey) and the EMD FP7 - a specialized variation of the F7A which was lenghtened to accomodate a larger water resevoir for its steam generators (a necessity for long distance passenger service like that of the Olympian Hiawatha). While E units could also have filled this role (and did, in later years), their A1A truck design (spreading their weight and giving them less traction) made them less than ideal for handling the steep grades of the Milwaukees route through the Rocky Mountains.