Prussian S 7

The class S 7 designates slightly different types of express train locomotives of the “Atlantic” type with four-cylinder compound engines. These either had the UIC wheel arrangement 2'B1 with a fixed trailing axle or 2'B1', where the trailing axle was designed as a Bissel axle. 

A variant was developed by Grafenstaden in Alsace and 79 examples were built between 1903 and 1905. Henschel was also involved in the production. What they had in common was the de Glehn design, in which the high and low pressure cylinders each drove an axle and could be controlled separately. These locomotives were in turn divided into two types. On the one hand, the short and wide firebox was completely behind the coupled wheel sets and the leading bogie had an inner frame. On the other, the firebox was long and narrow, allowing it to fit between the wheels. Here the bogie had an outer frame. One thing they had in common was that both versions had a fixed trailing axle. 

The other variant was developed by Hanomag and built 159 times between 1902 and 1907 by this company and by Linke-Hofmann-Busch. In contrast to the Grafenstaden locomotives, these were designed according to the Von Borries design. This means that all four cylinders were fitted on the same length and only worked on the first coupled axle. In addition, the trailing axle was movably mounted on these.

Although these locomotives were only certified for speeds of 100 or 110 km/h, speed records of up to 143 km/h were achieved. It was even possible to exceed the speed of the streamlined S 9 test locomotive with which it was compared. A disadvantage in operation soon became apparent that the adhesive weight of 30 tonnes was no longer sufficient for the increasing loads in express traffic. For this reason, the area of operation of the S 7 shifted towards normal passenger trains after the First World War. In the early 1920s, all locomotives were taken out of service, so that the Reichsbahn no longer included them in their renumbering plan.