Don't know much about the steamers, but the GP - 9's were unique for more than just dual controls. They also were ordered with larger fuel & water tanks than other Espee passenger geeps. This allowed them to run a round trip to Monterey without having to be refilled, and allowed Espee to retire the last steam - era facilities on the branch. This also let to a unique spotting feature of air reservoirs on the roof, aka ' Torpedo Boat ", and no dynamic brakes; Espee's only GP - 9's set up this way.