Bavarian S 3/6

The Bavarian S 3/6, later designated as the class 18^4-5, was probably one of the best-known express steam locomotives in Germany. Developed by the Munich company Maffei, it was not only procured by the Royal Bavarian State Railways from 1908, but even the Deutsche Reichsbahn commissioned new series until 1931.

Although more than 150 km/h had already been achieved with the S 2/6 trial locomotive in 1906, the speed to be reached with the S 3/6 was reduced to 120 km/h, which was more suitable for everyday use. Their performance program stipulated that a train weighing 400 tonnes should reach at least 115 km/h on the level. The same train should still be pulled at 95 km/h at 0.5 percent and at 65 km/h at one percent.

The locomotive was based on the Baden IV f and was given a driving wheel diameter of 1,870 mm as a compromise. This enabled the S 3/6 to cover long distances at a high line speed without excessive wear on the engine, without having to sacrifice too much traction for climbing. As with previous Bavarian express train locomotives, the running gear was built on a bar frame. 

Of the 159 locomotives of series a to o, only 18 locomotives of series d and e were built with wheel diameter of 2,000 mm in order to be able to drive at a constant speed of 120 km/h on flat lines between the largest cities in Bavaria. These were mainly the Munich-Nuremberg and Munich-Augsburg routes, on which there were hardly any significant inclines. They were soon given the nickname “Hochhaxige” (“the high-heeled one”) to distinguish them from the rest of the S 3/6.

Traction was provided by a four-cylinder compound engine, which enabled very smooth running and led to consumption that did not need to fear comparison with the later two-cylinder standard locomotives. Despite the significantly higher maintenance effort due to the internal cylinders, the S 3/6 continued to be procured in several series even after the Deutsche Reichsbahn was founded. This can be explained, among other things, by the fact that the new standard express train locomotive of the class 01 had an axle load of 20 tonnes and many main lines were not strengthened accordingly at the time. With an axle load of 18 tonnes, the last S 3/6 could also be used on almost all main routes until a lighter standard express locomotive became available with the class 03.

After the Second World War, all locomotives came to the Bundesbahn, where they were extensively modernized. Despite their still comparatively very good performance and economy, however, all of them were retired between 1961 and 1965, since a miscalculation during the rebuilding process had meanwhile made it necessary to reduce the boiler pressure and thus the power.