Prussian S 9 Altona 561 and 562

In search of a very fast steam locomotive for lighter trains, railway inspector Gustav Wittfeld developed the S 9 with the 4-4-4 wheel arrangement, which should not be confused with the S 9 that was mass-produced a few years later. The tender from the Association of German Engineers called for a machine that should be able to pull a 120-tonne train at at least 120 and if possible 150 km/h. The special thing about the two test locomotives was that they had an additional front driver's cab, which was intended for better observation of the route. The engine driver talked to the second driver via voice connection, who was in the rear cab in the usual position together with the fireman. Since the symmetrical wheel arrangement also allowed high reverse speeds, there was also a driver's cab at the end of the tender.

The first vehicle was provided with casing that was wedge-shaped at the front and from which it was hoped that a power saving of 250 to 300 hp would be achieved. There were a few windows in the side walls on both sides of the boiler so that this room could be used as a connecting passage. The tender also had an aisle and allowed to walk into the train. The second locomotive did not have the casing, but also had a wedge-shaped front on the front cab. The saturated engine was one of the few in Germany with three cylinders and compound steam expansion. The center cylinder took on the live steam and the two outer ones served as low-pressure cylinders. While the high-pressure cylinders of locomotives with two and four cylinders have a significantly smaller diameter, all three had the same dimensions here.

During the tests with the first locomotive, one quickly came to the realization that the expectations could not be met. The locomotive had about 1,400 hp, with which the 109-tonne train with three cars could be accelerated to 128 to 137 km/h on different runs. With a train that was twice as long and weighing 224 tonnes, it took more than ten minutes to reach the 110 km/h mark and the maximum speed was 118 km/h.

Since these achievements were not in proportion to the very complex construction, there was no series production. As a result, not only was the casing of the first engine removed, but the front cabs were also removed and the locomotives used like conventional steam locomotives. In addition, an adjustment of the offset between the cylinders was necessary, since at certain speeds there had been very strong shaking movements. A very similar construction, designed at the same time by Henschel, was a tank locomotive with the designation T 16. It had the wheel arrangement 4-6-4T and was intended for uphill stretches in Thuringia. Since it had an axle load of 20 tonnes, it could not be used on most routes and was returned to the manufacturer after a short time. The two S 9 were only used until 1918 and then scrapped.