In 1935 EMC manufactured a total of three prototypes of a heavy switcher, which were equipped with the Winton engine, of which the E-series had two. Two of these switchers had a 600 hp in-line 8-cylinder engine, while the third had a 900 hp V12. All had the same frame length, but with the more powerful version, the body was longer. A special feature of the hoods over the machinery was that the ceiling tapered to the driver's cab to improve visibility.

The production locomotives received an S for “six hundred” in the version with 600 hp, while the version with 900 hp received an N for “nine hundred”. There were also two different types of frames, which can be distinguished by the second letter in the type designation. The first version was cast by General Steel Castings and therefore has a C for “cast”, while the other was welded by EMC themselves and therefore has a W for “welded”.

The SC, SW, NC and NW types initially resulted from the combinations of engine and frame. Other versions of the more powerful variant were built, which differed mainly in terms of the electrics and were designated NC1, NC2, NW1 and NW1A. Two more copies were made from the NW4, which were lengthened and had an additional steam generator. These were used by the Missouri Pacific for switching passenger cars. A total of 175 series locomotives were produced up to 1939.

A single one was only given the type designation T and basically consisted of two power trains from the N series, which stood on four two-axle bogies with a driver's cab in the middle. With an output of 1,800 hp, it was intended to transfer freight trains between nearby marshalling yards and was not built in series because the long frame settled over time.