EMD SW1

The EMD SW1 was introduced in late 1938 as Electro-Motive Corporation's successor to its earlier SC and SW switcher models. Where those predecessors had relied on engines sourced outside the company, the SW1 marked a significant departure by incorporating EMD's newly developed 567 series prime mover, establishing a powerplant lineage that would define the company's locomotive production for decades. Production began in December 1938 and continued until November 1953, with a gap from March 1943 through September 1945 when wartime restrictions on railroad equipment manufacturing interrupted civilian locomotive production. Approximately 661 units were completed under the SW1 designation, with the total figure sometimes cited as higher when accounting for demonstrator units and closely related variants. The SW1 found buyers among a wide range of railroads across the United States, from major Class I carriers to small industrial and terminal operators. Its modest 600 horsepower output made it well suited for yard switching, industrial plant service, and light branch work rather than road service. Railroads such as the Southern Pacific, Boston and Maine, Chicago Burlington and Quincy, and numerous others placed orders during the production run. Several units also went to steel mills, grain terminals, and other industrial customers, reflecting the locomotive's utility beyond conventional railroad service. The SW1 holds an important place as the foundation of EMD's long-running SW switcher family. It was joined in later years by more powerful variants including the SW7 in 1949 and the SW8 in 1950, and its direct successor in the 600 horsepower class, the SW600, entered production in February 1954 immediately after SW1 output ceased. Numerous SW1 units demonstrated exceptional longevity, with examples remaining in active service well into the 2000s and beyond, and a substantial number have been preserved at railroad museums and heritage operations throughout the country.

The SW1 is powered by a six-cylinder version of EMD's 567 series engine, a two-stroke, mechanically aspirated diesel configured in a 45-degree V arrangement. The cylinders measure 8.5 inches in bore and 10 inches in stroke, yielding 567 cubic inches of displacement per cylinder, which gave the engine family its name. Running at 800 rpm, the six-cylinder variant produces 600 horsepower. Post-World War II production units used the refined 567A variant of the engine, though the external and operational characteristics remained largely consistent throughout the production run. Power is transmitted through a direct current generator to four traction motors arranged in a B-B wheel configuration, with two motors per truck. The locomotive rides on AAR Type A switcher trucks, a standard design common across much of the EMD switcher line. Several visible changes distinguish early SW1 units from later production examples. The earliest locomotives were delivered with a short exhaust stack that proved inadequate for clearing diesel fumes from the crew's line of sight, and these units were subsequently retrofitted with the taller conical stack that became standard on all later deliveries. The cab roof windows above the hood transitioned from a curved profile following the roofline to a flat-topped design around mid-1950. The taper of the hood as it met the cab also changed, from a two-stage taper on earlier units to a single continuous taper on later ones. Lighting evolved as well, with early units carrying a single large headlight and later production switching to twin sealed-beam headlights.