Dieselisation
Weighing against the cost of, and inertia against, replacing the large investment that railroads had in existing steam power were the dramatic increases in flexibility and efficiency with diesel. The fastest and most powerful steam locomotives were faster and more powerful than diesels; however, their range of efficient operation was severely limited. Diesels pro-rate their fuel usage to the length of trains, which a steam engine cannot do. Multiple-unit diesel power is scalable to power requirements with one locomotive crew; steam power is not. A high speed Hudson steam locomotive is good for only one situation, high speeds on level grades. The diesel locomotive can be operated by a single person, with no need of a fireman to run the boiler (two person cab crews may be required for other reasons). Also, diesels use much less fuel and no manpower when idling, something locomotives often do. Diesels can be parked running for days unattended, whereas steam engines must be constantly tended to if not completely shut down. Bringing a steam engine boiler up to operating temperature is often regarded as both an art and science, requiring much training and experience. A diesel is much simpler to start and shut down.
GE steam turbine locomotives
During test runs, the locomotives displayed excellent acceleration and an ability to maintain schedules better than conventional steam engines, although they also had serious reliability problems and relatively high maintenance costs. On one occasion, the two locomotives failed while hauling a train from Colorado to Omaha, necessitating a 2800-class Pacific steam locomotive to pull them along with the rest of the train for the remainder of the journey. The locomotives worked on several routes in a variety of different capacities, including both passenger and perishable freight service, although they never entered regular revenue service; in June 1939, the railroad returned them to GE in Chicago for what UP president W. M. Jeffers called "necessary modification and/or reconstruction".