The S2 was the largest steam locomotive ever with direct axle drive from a turbine. Delivered by Baldwin and Westinghouse in 1944, it was used by the PRR primarily in front of important express trains. Because the turbine was located directly between the second and third coupled axle and drove it via gears, there were only small mechanical losses. With an output of 6,900 hp, it was able to sustain over 100 mph, but the steam consumption of the turbine at low speeds was higher than that of conventional steam locomotives. In connection with the complicated maintenance, this initially led to the decommissioning in 1949 and the subsequent scrapping. 