  the pennsylvania railroad's class s2 was a steam turbine locomotive. one was built, #6200, delivered in 1944. the s2 was the sole example of the 6-8-6 wheel arrangement in the whyte notation, with a six-wheel leading truck, eight driving wheels, and a six-wheel trailing truck. the s2 used a direct-drive steam turbine; the turbine was geared to the center pair of axles with the outer two axles connected by side rods. the disadvantage was that the turbine could not operate at optimal speeds over the locomotive's entire speed range. the s2 was the largest direct-drive turbine locomotive design ever built. the locomotive was to be a 4-8-4, but wartime restrictions on light steel alloys increased weight until six-wheel leading and trailing trucks were needed. two turbines were fitted, one for forward travel and a smaller one for reversing at speeds up to 22 mph. a large boiler with a belpaire firebox and long combustion chamber was fitted. the turbine exhaust was piped through a set of four nozzles in the smokebox, providing an even draft for the fire and exiting through a unique quadruple stack. a worthington-pattern feedwater heater was fitted for increased 
Baldwin_locomotives Experimental_locomotives Individual_locomotives_of_the_United_States Passenger_locomotives Pennsylvania_Railroad_locomotives Scrapped_locomotives Standard_gauge_railway_locomotives Steam_locomotives_of_the_United_States Steam_turbine_locomotives Unique_locomotives