Duplex Locomotive - PRR Class S1

PRR Class S1

The next usage of the duplex type was the Pennsylvania Railroad's single S1, designed to meet a requirement to operate a 1,200 ton (1,100,000 kg) train at 100 mph on level track and able to accelerate to that speed easily. In excess of 4,000 hp (3.0 MW) was necessary for that requirement, and to meet it Baldwin and the PRR created possibly the largest passenger steam locomotive ever built, a 6-4-4-6 locomotive 140 feet 2+1⁄₂ inches (42.736 m) long and weighing 1,060,000 lb (480,000 kg) with tender. It was, in fact, too large to work over the majority of the PRR's system and was placed into service only between Chicago, Illinois and Crestline, Ohio. In service after December 1940, it proved powerful and capable but prone to wheelslip and surging, presaging the problems with later duplex designs. By and large, its flaws were written off as simply the teething troubles of an early, first-cut prototype. It was taken out of service in 1945.