In 1935, EMC built a total of five machines to test the use of large mainline diesel locomotives under everyday conditions. These were two company demonstrators, one for the Baltimore & Ohio and a double set for the Santa Fé. Since there was no production capacity for large diesel locomotives at that time, they turned to General Electric and the St. Louis Car Company.
The basic idea was to install two diesel engines, each with its own generator and about 50 percent more total power, instead of just one diesel engine. Since the engines were less heavily loaded on average, less wear and tear and a longer service life could be expected. If one engine or generator failed, the locomotive could continue to run with the other. The concept of having a driver's cab at each end was new, but was not pursued on later American diesels.
For cost reasons, the two demonstrators had got simple, box-shaped bodies like earlier boxcabs. For the first time, they were given multiple controls, so that both locomotives could be controlled by one driver at the same time. In fact, they were often used together to achieve the same performance as a large steam engine. After extensive testing, they were scrapped in 1938.
The Baltimore & Ohio received a locomotive identical to the first two and was numbered 50. It soon got a slanted fairing on one end, also known as a “Shovel Nose”. This cladding was removed again during World War II. In this form, the locomotive was still used for local freight and passenger trains for a while after the end of the war. It later ended up in the National Museum of Transportation in St. Louis, Missouri and can still be found there today.
The double locomotive of the Santa Fé was managed as one complete unit and received the number 1. It had streamlined shapes, covered bogies and an attractive color scheme. The company's route network had long stretches that led through deserts and mountains and offered good conditions for testing the new technology. Their advantage over steam locomotives was that they were not dependent on water supplies and could cover long distances with one tank of diesel.
The 2,226.6-mile route, which was regularly run with passenger trains, served as preparation for the later operation of the streamlined trains and revealed a few teething problems. The fairing on the bogies soon had to be removed due to repeated overheating problems. The hood over the air intakes above the driver's cabs also impeded cooling, so that additional air intakes on the roof were necessary. The unit was later reinforced with one of the EMC demonstrators. In 1938, one driver's cab was removed and a “Bulldog Nose” formed, as was also found on the later production locomotives. In addition, both bogies each received a leading axle. The locos were returned to EMD in 1953 and converted to booster units.
The locomotives provided many insights which were implemented in the series production of the E series. These were powered by the same Winton engines, initially each with 900 hp, but bogies with a central carrying axle. The multiple control was soon adopted by all manufacturers and is still used today in almost all North American diesel locomotives in a form that has hardly changed.