EMD E-unit

EMD E-unit

EMD E-units were a line of passenger train diesel locomotives built by the General Motors Electro-Motive Division (EMD) and its predecessor the Electro-Motive Corporation (EMC). Final assembly for all E-units was in La Grange, Illinois. Production ran from May, 1937, to December, 1963. The name E-units refers to the model numbers given to each successive type, which all began with E. The E originally stood for eighteen hundred horsepower (1300 kW), the power output of the earliest model, but the letter was kept for later models of far higher power ratings.

The predecessors of the E-units were the EMC 1800 hp B-B locomotives built in 1935. These had similar power and mechanical layouts to the E-units, but enclosed in boxcab bodies and with AAR type B two-axle trucks.

EMC also introduced the TA model in 1937, selling six to the Rock Island. This had very similar carbody styling, but otherwise had more in common with UP M-10001, M-10002, and M-10003 through M-10007, in that it was a 1,200 hp (900 kW), single-engined unit on B-B trucks instead of the E-units' A1A-A1A wheel arrangement. It is therefore not part of the E-unit series.

Like many early passenger locomotives, E-units used two engines to achieve the rated power. This was due to the technology of the time limiting the power that could be developed by a single engine. Even so, while E-units were used singly for shorter trains, longer trains needed multiple locomotive units; many railroads used triple units. E-units could be purchased either with or without driving cabs; units with a cab are called A units or lead units, while cabless units are called B units or booster units. B units did contain simple controls for hostling purposes, but they could not be so controlled on the main line. The locomotive units were linked together with MU cables which enabled the crew in the lead unit at the front to control the trailing units. Railroads tended to buy either ABA sets (two driving cab-equipped units facing in opposite directions with a booster in between) or ABB sets (a single driving cab with a pair of boosters). The former did not need to be turned to pull in either direction, but B units were cheaper than A units and they made for a smoother line to the train.