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 Rocket passenger train, which travelled as a unified train from Chicago, Illinois, to Limon, Colorado, which then divided. One section went 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, and 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-series E6B (B unit) but with an operating cab, headlight, pilot, and other features to enable it to operate as an independent locomotive.

Rock Island No. 751 at Joliet, Illinois in October 1966
Type and origin
Power typeDiesel-electric
BuilderElectro-Motive Corporation (EMC)
Build date1940
Total produced2
  • New: A1A-3
  • Later: A1A-A1A
Gauge4 ft 8 12 in (1,435 mm) standard gauge
Prime moverEMD 567, 1 off, later 2 off
Engine typeV12 Two-stroke diesel
Performance figures
Power output
  • New: 1,000 hp (750 kW)
  • Later: 2,000 hp (1,491 kW)
OperatorsRock Island
Numbers750 and 751
DeliveredJune 1940
DispositionBoth scrapped 1973–74

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.


  • Marre, Louis A. (1995). Diesel Locomotives: The First 50 Years. Kalmbach Publishing Co. p. 123. ISBN 0-89024-258-5.
  • Marre, Louis A. (1982). Rock Island Diesel Locomotives 1930–1980. Cincinnati, Ohio: Railfax, Inc. pp. 93–94. ISBN 0-942192-00-1.
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