The EMC AB6 was a type of diesel locomotive built exclusively for the Chicago, Rock Island and Pacific Railroad (the "Rock Island Line") by General Motors' Electro-Motive Corporation and delivered in June 1940. Two examples were built, numbered #750 and #751. They were built for the Rocky Mountain Rocketpassenger train, which travelled as a unified train from Chicago, Illinois, to Limon, Colorado, but then divided; with one segment going to Colorado Springs, Colorado, and the other to Denver, Colorado. The Rock Island desired a locomotive that could look like an integrated part of the train during the Chicago-Limon portion of the route, but could then be operated independently to take three cars to Colorado Springs. A regular, cab-equipped A-unit could have been purchased, but that would have ruined the streamlined look of the train, so the RI had EMC build a flat-fronted locomotive based on an E-seriesE6B (B unit) but with an operating cab, headlight, pilot, and other features to enable it to operate as an independent locomotive.
Since the small three- and four-car trains the units would have to haul independently were very light, the AB6 pair were built with only one 1,000 hp EMC 567 V12 engine, and a baggage compartment where the second engine would have been. Later, with increasing trainloads, the baggage compartment was replaced with a second engine.
In 1965, the units had their steam generators replaced with head-end power and were reassigned to push-pull suburban service in the Chicago area. In this form, they lasted until the mid-1970s.
References
Marre, Louis A. (1995). Diesel Locomotives: The First 50 Years. Kalmbach Publishing Co. p. 123. ISBN0-89024-258-5.
Marre, Louis A. (1982). Rock Island Diesel Locomotives 1930–1980. Cincinnati, Ohio: Railfax, Inc. pp. 93–94. ISBN0-942192-00-1.
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