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.
Electro-Motive Diesel
Passenger trains made little money for the railroads, but replacement of steam engines with reliable Diesel units could provide railroads with a crucial difference for profitability. With standardized production of locomotives, EMC simplified the processes for ordering, manufacturing, and servicing locomotives and introduced economies of scale that would lower unit costs. EMC offered support services including financing, training, and field maintenance that would ease the transition from steam to Diesel and boost their market in the last years before US entry into World War II. The performance of the new 567 engine in passenger locomotives also built confidence in the viability of Diesel power for freight service.