CRI&P's EMC AB6 No. 751 in suburban commuter service at Joliet, IL, October 16, 1966.

(Roger Puta, courtesy Marty Bernard, Public domain, via Wikimedia Commons)


EMC logo.


The EMC AB6 was a type of diesel locomotive built exclusively for the Chicago, Rock Island and Pacific Railroad (the "Rock Island Line") by the Electro-Motive Corporation and delivered in June 1940. Two examples were built, numbered No. 750 and No. 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.

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 and were eventually scrapped.


AB6 751 in later Rock Island livery and in suburban service, 1960's. (, Fair use, 17 U.S.C. § 107, via W. Lenheim Collection)

The Rock Island's AB6 No. 751 in a different paint scheme, now used in commuter service, Chicago, 1970. Photo by Ken Christ. (Audio-Visual Designs, Earlton, NY, Public domain, W. Lenheim Collection)


Type and origin

Power type Diesel-electric
Builder Electro-Motive Corporation (EMC)
Build date 1940
Total produced 2
​• AAR
New: A1A-3
Later: A1A-A1A
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Prime mover: EMD 567, x 1 off, later x 2
Engine type: V12 Two-stroke diesel
Cylinders: 12
Performance figures
Power output New: 1,000 hp (750 kW)
Power Output Later: 2,000 hp (1,491 kW)
Operators: Rock Island
Numbers: 750 and 751
Delivered: June 1940
Retired: mid-1970s
Disposition: Both scrapped 1973–74