The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...

s of 4-4-6-4 wheel arrangement built between 1944 and 1945. They were the largest non- articulated locomotives ever built and the most powerful locomotives ever static tested, producing 7,987 cylinder

horsepower Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

(5,956 kW) on the PRR's static test plant. They were by far the most successful duplex type. The duplex propensity to slip was combated by an automatic slip control mechanism that reduced power to the slipping unit. The Q2 locomotive was 78% more powerful than the locomotives that PRR had in service at the time, and the company claimed the Q2 could pull 125 freight cars at a speed of ."4-Cylinder Engine Has 78% More Power."
''Popular Mechanics'', December 1944, p. 13. These were an improved version of the previous Q1 class, which was a 4-6-4-4 dual-purpose engine instead of a 4-4-6-4 freight engine. Despite the overall success, the Q2s were all out of service by 1951. With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s, but with far-higher operating and maintenance costs. The final Q2, 6199's power output is 7,987 hp. All have been scrapped and none were preserved.

References

{{PRR locomotives 4-4-6-4 locomotives Duplex locomotives Experimental locomotives Q2 Steam locomotives of the United States Scrapped locomotives Freight locomotives Standard-gauge locomotives of the United States Streamlined steam locomotives Railway locomotives introduced in 1944