The Pennsylvania Railroad's S2 class was a steam turbine locomotive designed and built in a collaborative effort by Baldwin Locomotive Works and Westinghouse Electric & Manufacturing Company, as an attempt to prolong the dominance of the steam locomotive by adapting technology that had been widely accepted in the marine industry. One was built, #6200, delivered in September 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 provided by the Westinghouse Electric & Manufacturing Company, geared to the center pair of axles with the outer two axles connected by side rods; the fixed gear ratio was 18.5:1. Such design was to prevent energy loss and S2 achieved a mechanical efficiency of 97% which means only 3% of steam energy was lost within the propulsion equipment. The disadvantage of direct-drive steam turbine was that the turbine could not operate at optimal speeds over the locomotive's entire speed range. The S2 was the largest, heaviest and fastest direct-drive turbine locomotive design ever built. Design specification 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; its construction was also delayed by World War II. Construction of the locomotive took place at the Baldwin plant in Eddystone. Two turbines were fitted, one for forward travel and a smaller one for reversing at speeds up to . Superheated steam at a rate of about 2,000 pounds per hour was directed onto the turbine blades through 4 nozzles; thousands of turbine blades transmitted steam energy to the transmission gear. The maximum rotation speed of the forward turbine is 9,000 rpm, developing 6,900 hp; the reverse turbine generates 1,500 hp at 8,300 rpm. A monitoring system ensured that the forward turbine could only be started when the reverse turbine was switched off. Weight of propulsion equipment was 39,000 lbs., or 5.65 lbs/hp. A large boiler with a Belpaire firebox and long combustion chamber was fitted. An automatic lubrication system was installed, connecting the transmission case, where the driving gear wheels were immersed in a lubricant reservoir filled with lubricating oil. Lubricant goes through all lubrication points, including roller bearings on all axles via the filtered pipes with the help of two steam pumps. A Worthington-pattern feedwater