TheEMC AB6was a type ofdiesel locomotivebuilt exclusively for theChicago, Rock Island and Pacific Railroad(the "Rock Island Line" ) byGeneral Motors'Electro-Motive Corporationand delivered in June 1940. Two examples were built, numbered #750 and #751. They were built for theRocky Mountain Rocketpassenger train,which travelled as a unified train fromChicago, Illinois,toLimon, Colorado,which then divided. Onesectionwent toColorado Springs, Colorado,and the other toDenver, 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 anE-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 567V12 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 theirsteam generatorsreplaced withhead-end powerand were reassigned topush-pullsuburban service in the Chicago area. In this form, they lasted until the mid-1970s and were eventually scrapped.
