PRR Q1
The PRR also desired to apply the duplex principle to freight haulage, and the Q1 was the first experiment in that direction. It was a 4-6-4-4 fast freight locomotive delivered in May 1942. Like the B&O's George H. Emerson it had the second pair of cylinders facing backwards, and all were fitted with standard Walschaerts valve gear. The wheels were of 77 inches (2.0 m) diameter (ill suited for freight hauling) and the engine was streamlined more like a passenger engine.
Read more about this topic: Duplex Locomotive