Early Electro-Motive Corporation switchers were built with Winton 201-A engines. A total of 175 were built between February 1935 and January 1939. Two main series of locomotives were built, distinguished by engine size and output: the straight-8, 600 hp (450 kW) 'S' series, and the V12, 900 hp (670 kW) 'N' series. Both were offered with either one-piece cast underframes from General Steel Castings of Granite City, Illinois, denoted by 'C' after the power identifier, and fabricated, welded underframes built by EMC themselves, denoted by 'W'. This gave four model series: SC, SW, NC and NW. Further developments of the 900 hp (670 kW) models gave model numbers NC1, NC2, NW1, and NW1A, all of which were practically indistinguishable externally from the others, as well as a pair of unique NW4 mo