The EMC EA/EB is an early passenger train-hauling diesel locomotive built from May 16, 1937, to 1938 by Electro-Motive Corporation of La Grange, Illinois for the Baltimore and Ohio Railroad. They were the first model in a long line of passenger diesels of similar design known as EMD E-units. Each locomotive unit developed 1,800 horsepower (1,300 kW) from two 900 hp (670 kW) Winton 201-A diesel engines, driving the wheels through an electric transmission—the generator driven by each engine provided current for traction motors. The locomotives were of A1A-A1A wheel arrangement—two three-axle trucks of which only the outer two axles were powered. Six two-unit 3,600 hp (2,700 kW) locomotives were produced, each consisting of a lead cab-equipped EA A unit and a cabless booster EB B unit. They were numbered 51 through 56; the A units bore the bare number and the B units the number followed by 'X'.

A diesel locomotive is a type of railway locomotive in which the power source is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels. The most common are diesel-electric locomotives and diesel-hydraulic.