EMD E6A/E6B

The EMD E6 emerged in late 1939 as the seventh generation of Electro-Motive's passenger diesel lineup, a series of locomotives that had been steadily refining the concept of high-speed diesel-powered passenger service since the mid-1930s. Production of the cab unit, designated E6A, began in November 1939 and continued through September 1942, with 91 examples completed. The booster version, the E6B, entered production in April 1940 and ran through February 1942, yielding 26 units. Together these figures account for the roughly 118 A-units and 5 B-units that sources cite for the model, though some variation exists in tallies depending on how certain special variants are classified. The locomotives were built at Electro-Motive's La Grange, Illinois facility, initially under the Electro-Motive Corporation banner before that entity became the General Motors Electro-Motive Division during the production run. Several notable variants were produced alongside the standard E6A and E6B. The Missouri Pacific received a custom unit designated the EMC AA, which carried only a single prime mover and 1,000 horsepower, with a baggage compartment occupying the space where the second engine would otherwise have been installed. The Chicago, Rock Island and Pacific Railroad took delivery of a pair of unusual power cars called the EMC AB6, which were mechanically similar to the single-engine AA concept but wore blunt boxcab noses rather than the streamlined carbody of the standard E6A. These AB6 units worked as boosters on the Rocky Mountain Rocket service, accompanying conventional E6A locomotives between Chicago and Limon, Colorado, where the consist was divided. The E6 shared the distinctive slanted nose profile of its immediate predecessors, the E3, E4, and E5, a design characteristic that later gave these models the informal collective nickname of slant-nose units among enthusiasts and historians. This aesthetic separated them from the subsequent E7 and later E-units, which adopted the rounder bulldog nose more commonly associated with EMD's postwar F-series freight diesels. Despite being superseded relatively quickly by the E7 beginning in 1945, the E6 represented the mature expression of prewar passenger diesel design, and examples served railroads including the Atchison, Topeka and Santa Fe, the Baltimore and Ohio, and the Louisville and Nashville, among others. Two E6A units are known to survive: one former Rock Island locomotive in storage and undergoing restoration, and a Louisville and Nashville unit on static display at the Kentucky Railway Museum in New Haven, Kentucky.

The E6A and E6B were powered by a pair of General Motors 567-series prime movers, each a 12-cylinder, two-stroke diesel engine producing 1,000 horsepower, for a combined output of 2,000 horsepower. Each engine drove its own main generator, which in turn supplied current to the locomotive's DC traction motors. The wheel arrangement was A1A-A1A, meaning each three-axle truck had powered outer axles and an unpowered center axle, a configuration chosen to distribute the locomotive's weight over more rail contact points without requiring additional traction motors. This arrangement was well suited to the lightly laid trackage and sensitive passenger equipment of the era, reducing the risk of track damage while maintaining adequate tractive effort for high-speed service. The carbody of the E6 followed the streamlined aesthetic conventions of the late 1930s, with a nose that was notably more angled and tapered when viewed in profile compared to the designs that would follow after World War II. The cab units stretched to a length that accommodated two complete engine and generator sets within a single carbody, along with the engineer's cab, dynamic brake equipment, and steam generator for passenger car heating. The booster B-units omitted the operating cab entirely, allowing slightly more flexibility in consist arrangements while sharing all major mechanical components with the A-unit. The 567 engine family introduced in this period proved to be an extraordinarily durable design foundation, continuing in various forms to power EMD products for decades after the E6's production concluded.

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