Diesel locomotives appeared first in 1913, built for continuous operation and may require the ability to use poor quality fuel in some situations. Some locomotives use a two-stroke diesel engine, but many modern diesel locomotives are designed diesel-electric locomotives; the diesel engine is used to power an electric generator that in turn powers electric traction motors with no mechanical connection between diesel engine and traction. Diesel engines have eclipsed steam engines as the prime mover on all non-electrified railroads in the industrialized world.
