With the first generation of E-units, EMC made on step away from the custom-built diesel streamliners towards standardized, mass-produced passenger locomotives. As EMC's new owner GM was convinced that styling was more important than technical advances, they put much effort into the streamlined nose. Technically, they still had many similarities to the earlier, integrated power units of the famous streamliner trains. The designation “E” came from “eighteen hundred”, what was the total number of horsepower per unit.

Power still came from the proven Winton 201-A two-stroke engines. Each unit had two 900 hp engines, which had one generator each and powered two three-axle bogies with an A1A arrangement. Each locomotive was either an A-unit with a cab at one end or a B-unit with no cab at all. Usually, two or three units were coupled together and operated by a single crew to haul a heavy passenger train. In total these had 3,600 or 5,400 hp, what was the typical power range of the big steam passenger locomotives of the time.

In 1937 and 1938, three models were built for three customers which were identical for the most part. The Baltimore & Ohio received six EA and six EB. The E1 was developed for the ATSF, which received eight A-units and only three B-units. These were rebuilt to E8 in 1952 and 1953. For the famous trains “City of San Francisco” and “City of Los Angeles”, two A-units and four B-units of the E2 were jointly owned by the Union Pacific, Chicago & North Western and the Southern Pacific. Five of these were also later rebuilt to E7 or E8. These optically differed from the EA and E1 by having the bulldog nose also seen on later EMD locomotives.