| EMC AB6 | |
| Powertype: | Diesel-electric |
| Builder: | Electro-Motive Corporation (EMC) |
| Builddate: | 1940 |
| Totalproduction: | 2 |
| Enginetype: | V12 Two-stroke diesel |
| Primemover: | EMC 12-567, 1 off, later 2 off |
| Cylindercount: | 12 |
| Operator: | Rock Island |
| Fleetnumbers: | 750 and 751 |
| Deliverydate: | June 1940 |
| Retiredate: | mid-1970s |
| Disposition: | Both scrapped 1973–74 |
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.
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.