The S2 was the sole example of the 6-8-6 wheel arrangement in the Whyte notation, with a six-wheel leading truck keeping the locomotive stable at speed, eight powered and coupled driving wheels, and a six-wheel trailing truck supporting the large firebox.

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.

The S2 was the largest, heaviest and fastest 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; its construction was also delayed by World War II.

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.

Apparently, these weren't adequate, so a much-larger pair which look like the "elephant ears" used on New York Central class S1b 4-8-4 Niagara and Union Pacific FEF-3 4-8-4 was added at Altoona Works in December, 1946.

In order to reduce the crew's workload, a "Fluid Pressure Control System" (U.S. patent 2,515,962) designed by Westinghouse engineer Harry C. May was installed on the locomotive.

During a test run officially arranged by PRR on 30 March 1945, S2 #6200 towing a dynamometer car was able to pull a 17-car train over a distance of 48 kilometers (level track) at a speed of 110 mph (180 km/h) between Fort Wayne and Chicago.

Cox, a British locomotive engineer, once traveled on the footplate and reported that "100mph was maintained and exceeded for 12 consecutive minutes".

PRR S2 #6200, as an experimental prototype of a direct-drive steam turbine locomotive, ran 103,000 miles in total before it was completely withdrawn from service in August, 1949 and would soon await the scrapper's torch.

It was similar to both of the original turbine models but the 681 has Lionel's Magne-Traction feature which makes the wheels magnetic.

The 682 was basically a 681 but with valve gear on the wheels and a white stripe painted on both sides.