The EMC AB6 was a type of

diesel locomotive A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving whee ...

built exclusively for the

Chicago, Rock Island and Pacific Railroad The Chicago, Rock Island and Pacific Railroad (CRI&P RW, sometimes called ''Chicago, Rock Island and Pacific Railway'') was an American Class I railroad. It was also known as the Rock Island Line, or, in its final years, The Rock. At the end ...

(the "Rock Island Line") by

General Motors The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...

Electro-Motive Corporation Progress Rail Locomotives, trade name, doing business as Electro-Motive Diesel (EMD), is an American manufacturer of diesel-electric locomotives, locomotive products and diesel engines for the rail industry. The company is owned by Caterpillar Inc ...

and delivered in June 1940. Two examples were built, numbered #750 and #751. They were built for the '' Rocky Mountain Rocket''

passenger train A passenger train is a train used to transport people along a railroad line. These trains may consist of unpowered passenger railroad cars (also known as coaches or carriages) hauled by one or more locomotives, or may be self-propelled; self p ...

, which travelled as a unified train from

Chicago, Illinois (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

, to

Limon, Colorado Limon is a statutory town that is the most populous municipality in Lincoln County, Colorado, United States. The population was 1,880 at the 2010 United States Census. Limon has been called the "Hub City" of Eastern Colorado because Interst ...

, which then divided. One

section Section, Sectioning or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...

went to

Colorado Springs, Colorado Colorado Springs is a home rule municipality in, and the county seat of, El Paso County, Colorado, United States. It is the largest city in El Paso County, with a population of 478,961 at the 2020 United States Census, a 15.02% increase since ...

, and the other to

Denver, Colorado Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...

. 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 E series may refer to: * BMC E-series engine, a series of automobile engines * Electronic E series of preferred numbers, a series of preferred values for electronic components such as resistors, capacitors, inductors, zener diodes * Entwicklung seri ...

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 A V12 engine is a twelve-cylinder piston engine where two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engines are more common than V10 engines. However, they are less common than V8 engines. The f ...

, 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.

References

* * {{EMD cab and cowl A1A-3 locomotives A1A-A1A locomotives AB6 Chicago, Rock Island and Pacific Railroad Passenger locomotives Diesel-electric locomotives of the United States Railway locomotives introduced in 1940 Scrapped locomotives Standard gauge locomotives of the United States