Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
Steam turbine locomotive
General Electric built two steam turbine-electric locomotives with a 2+C-C+2 (4-6-6-4) wheel arrangement for the Union Pacific Railroad in 1938. These locomotives essentially operated as mobile steam power plants and were correspondingly complex. They were the only condensing steam locomotives ever used in the United States. A Babcock & Wilcox boiler provided steam, which drove a pair of steam turbines which powered a generator, providing power to the electric traction motors that drove the wheels, as well as providing head-end power for the rest of the train. Boiler control was largely automatic, and the two locomotives could be connected together into a "multiple unit", both controlled from a single cab. The boiler was oil-fired, and the fuel was "Bunker C" heavy fuel oil, the same fuel used in large vessels, and also the fuel which was later used in Union Pacific's gas turbine-electric locomotives. Union Pacific accepted the locomotives in 1939, but returned them later that year, citing unsatisfactory results. The GE turbines were used during a motive power shortage on the Great Northern Railway in 1943, and appear to have performed quite well. However, by the end of 1943, the wheels of both locomotives were worn to the point of needing replacement, and one of the locomotive's boilers developed a defect. The locomotives were returned to GE and dismantled.