Diesel locomotive
Diesel locomotives offer significant operating advantages over steam locomotives. They can safely be operated by one person, making them ideal for switching/shunting duties in yards (although for safety reasons many main-line diesel locomotives continue to have 2-man crews: an engineer and a conductor/switchman) and the operating environment is much more attractive, being quieter, fully weatherproof and without the dirt and heat that is an inevitable part of operating a steam locomotive. Diesel locomotives can be worked in multiple with a single crew controlling multiple locomotives in a single train — something not practical with steam locomotives. This brought greater efficiencies to the operator, as individual locomotives could be relatively low-powered for use as a single unit on light duties but marshaled together to provide the power needed on a heavy train. With steam traction a single very powerful and expensive locomotive was required for the heaviest trains or the operator resorted to double heading with multiple locomotives and crews, a method which was also expensive and brought with it its own operating difficulties.
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".