EMC AB6

{{Short description|Unique Diesel Railroad Locomotive}}

{{for|the United States Coast Guard patrol boat|USCGC Kangaroo (1917)}}

{{no footnotes|date=July 2016}}

{{Infobox locomotive

| name = EMC AB6

| powertype = Diesel-electric

| image = CRI&P 751 (AB6) at Joliet, IL on October 16, 1966.jpg

| caption = Rock Island {{Abbr|No.|Number}} 751 at Joliet, Illinois in October 1966

| gauge = {{track gauge|ussg|allk=on}}

| builder = Electro-Motive Corporation (EMC)

| builddate = 1940

| totalproduction = 2

| aarwheels = {{ubl|New: A1A-3|Later: A1A-A1A}}

| enginetype = V12 Two-stroke diesel

| primemover = EMC 12-567, 1 off, later 2 off

| cylindercount = 12

| poweroutput = {{ubl|New: {{convert|1000|hp|kW|abbr=on}}|Later: {{convert|2000|hp|kW|0|abbr=on}}}}

| 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.