The TA was a small series of six four-axle diesel-electric passenger locomotives ordered by the Rock Island for their “Rock Island Rocket” trains. They were built at the same time as the EA, E1 and E2, but did not have the middle carrying axle in their bogies and only had a single 16-cylinder 1,200 hp engine. The “T” in the type designation stood for “twelve hundred”.

The six locomotives of the Rock Island carried a livery in maroon, light red and silver. When new rolling stock was introduced for the Rocket trains, the locomotives could still be used on their own and came into local and suburban service. They were finally retired in 1957 and 1958 and scrapped. Although no other customers did order the TA, it can be seen as an important step between the customer-tailored diesel locomotives and the later standard types.