Saxon XII H, HV and H1

Around the turn of the century, class X V locomotives with a 4-4-2 wheel arrangement were developed in Saxony for use in front of express trains. Since these had too little traction in the hilly country, the XII H with a 4-6-0 wheel arrangement was developed a few years later. They were among the first Saxon locomotives to use superheated steam and were built in three different types to compare the suitability of different power plants.

The actual XII H was made in 1906 in six units and had a four-cylinder engine with simple steam expansion, which was rarely found in Germany, as it was also tested a few years later on the Prussian S 10. In line with the spirit of the times, the locomotives were built with a cone-shaped cladding on the smokebox door and a wind cutter on the front of the cab. With a maximum speed of 100 km/h it was possible to tow trains of 300 tonnes. Despite this performance, it turned out that consumption was very high due to the greater heat loss through the four cylinders. In addition, it was later realized that aerodynamic optimizations in steam locomotives only brought measurable advantages at speeds of significantly more than 100 km/h.

From 1908 the XII HV was developed, fitted with a four-cylinder compound engine. In order to be able to make better use of the two-stage steam expansion, the boiler pressure was increased to 15 bars. The aerodynamic optimizations of the XII H were also used on it, but they were dispensed with on the later locomotives and the fairings were later removed from the older locomotives as well. Despite the higher boiler pressure, it turned out that the XII HV had a lower output than the XII H. While the latter could move 300 tonnes at 100 km/h, the compound version only managed 270 tonnes at the same speed. However, significantly lower fuel consumption values were now achieved, which is why series production of the XII HV was started. By 1914, 42 locomotives had been built.

While production of the composite version was already underway, the XII H1 was developed in view of the positive experiences with the P 8 in Prussia. Seven of them were already being built in 1909 and they only had two large cylinders. Despite the same wheel arrangement and similar dimensions, it was structurally less related to the other two variants than to the class X H1 Atlantic locomotive developed at the same time. Thus, it had a larger boiler and had the largest grate surface of all variants, but at the same time it was the lightest.

The result of the two cylinders was a fuel consumption that was between that of the other two versions and running characteristics which could not keep up with locomotives with four cylinders, with significantly cheaper production and simpler maintenance. However, due to its boiler, it was considerably more powerful than its sisters and could tow up to 450 tonnes at top speed. Although there was no series production, this experience was used in the development of the later XII H2 passenger locomotives and the two-cylinder engine was used there in conjunction with smaller coupling wheels, also with the 4-6-0 wheel arrangement.

After the takeover by the Reichsbahn, the three sub-types each received the class designations 17⁶, 17⁷ and 17⁸. Due to their smaller numbers, the XII H and XII H1 were retired by 1928 and 1929, respectively. The decommissioning of the XII HV began as early as 1925, but one could not do without all of them right from the start and kept the last pieces until 1936. Outside of regular operational service, a single XII H with the number 17 604 survived until 1956. It was used as a heating locomotive in Dresden-Altstadt.