In the late fifties, Fairbanks-Morse tried to establish a new type of lightweight diesel locomotives for passenger service. Power came from FM's opposed piston diesel engine that delivered 1,600 hp in this case. The prime mover was to be operated at constant RPM, so 400 hp could be used to generate electricity for the train and 1,200 hp were available for traction. The locomotives were optionally offered with contact shoes for operation in non-diesel areas like New York's Grand Central Terminal. The idea was to put one of these locomotives onto each end of a lightweight Talgo train that was to be built in the USA.

The New Haven ordered two for their “John Quincy Adams” train which were classed EDER-7 and got the numbers 3100 and 3101. They had contact shoes, while the two locomotives of the Boston & Maine were diesel-only and numbered 1 and 2. These were used for the train called “Speed Merchant”. The B&M used these units until 1964, but the NH stored their locomotives after a short time and sold their Talgo train to Spain. They were replaced by the EMD FL9 with conventional coaches.