The S 2/6 was a one-off that was only intended for testing higher speeds. It was ordered in December 1905 and developed and built within just four months. In terms of wheel arrangement and driving wheel diameter, it corresponds to the Prussian test locomotive S 9, with which high-speed tests had been undertaken shortly before. In contrast to this, however, the S 2/6 was otherwise based on near-series technologies.

In addition to the two coupled wheel sets with 2,200 mm wheels, the measures used in various places to reduce air resistance are distinguishing features of the locomotive. Other express locomotives of the time also had a cone-shaped smokebox door and a driver's cab tapered at the front, but there was a smooth transition from the boiler to the driver's cab. The streamlined cladding of the chimney, steam dome and cylinders went even further.

With a large grate area compared to other locomotives, a very good evaporation performance was obtained. Together with the four-cylinder compound engine, a calculated indicated output of up to 2,200 hp was achieved during test drives. On July 2, 1907, with four wagons with a total weight of 150 tonnes it traveled at a speed of 154.5 km/h. This value was a world record and caused a stir internationally.

Immediately after the test runs, the S 2/6 was put into regular use, where it was able to reach a speed of 120 km/h with trains weighing 360 tonnes. In operation in Bavaria, it was particularly unpopular with the planning staff because it was a one-off and its characteristics differed greatly from the other locomotives used. Compared to the S 3/6, the S 2/6 had more power, but with only two coupled axles it could generate less traction, which made planning the simultaneous use of both locomotives very difficult.

In 1910 the locomotive was relocated to the Palatinate network, which belonged to Bavaria, and was more popular there. On the Reichsbahn it would have become class 15, in which it would have been the only locomotive with a 4-4-4 wheel arrangement. However, after returning to Bavaria, it was decommissioned, refurbished and taken to the Nuremberg Transport Museum in 1925, where it is to this day.

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.

Later state after the rebuilding

Locomotive Magazine, August 1934

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.