EMC 1800 hp B-B

Electro-Motive Corporation (later Electro-Motive Division, General Motors) produced five 1800 hp B-B experimental passenger train-hauling diesel locomotives in 1935; two company-owned demonstrators, #511 and #512, the Baltimore and Ohio Railroad's #50, and two units for the Atchison, Topeka and Santa Fe Railway, Diesel Locomotive #1. The twin engine power unit layout and multiple unit control systems developed with the B-B locomotives were soon adopted for other locomotives such as the Burlington Route's Zephyr locomotives built by the Budd Company in 1936 and EMC's own EMD E-units introduced in 1937. The B-B locomotives worked as proof-of-concept demonstrators for diesel power with the service loads of full size trains, breaking out of its niche powering the smaller custom Streamliners.

In 1935, EMC was just starting to switch from a design and marketing company to a locomotive-building company, and could not yet produce the locomotives it designed. Construction of carbodies for EMC demonstrators #511 and #512, and B&O #50 was therefore subcontracted to General Electric's factory in Erie, Pennsylvania, and AT&SF #1 to St. Louis Car Company. Like most boxcabs, they initially had control cabs at both ends, a feature that would rarely be repeated in North American locomotives, although it would become common elsewhere. Power was provided by twin 900 hp (670 kW) 12 cylinder Winton 201-A diesel engines in each power unit, exceeding by 50% the most power that could be attained with a single engine at that time. The added "headroom" in power extended the life of mechanical parts, which was a critical issue with early diesel engines in locomotives. The units were built with AAR type B two-axle trucks. As development design locomotives, modifications were frequently made to them to overcome various teething problems; the EMC demonstrators spent considerable time in aluminum paint substituting for the units under modification.