B unit
The motive power for the "Rocket" was unusual. The Rock Island assigned an EMC E6 and EMC AB6 to haul the train. The AB6s, unique to the Rock Island and this route, were flat-fronted, similar to a B unit, but with a cab and capable of independent operation. It could operate behind an A unit without ruining the streamlined profile of the train, but then pull the Colorado Springs section after the separation in Limon.