With 96 examples, the IV K was the most numerous narrow-gauge steam locomotive in Germany. Its special feature is the design based on the Meyer design with two bogies, which was due to the requirements for increased tractive effort. Since the six-coupled locomotives of classes I K and III K that had been used up to that point were no longer sufficient for all operations, the answer was a new locomotive with four coupled axles. In order to achieve good negotiation of curves, the special arrangement of the chassis was used.
In contrast to the Mallet, both parts of the chassis of this type of locomotive were designed as swiveling bogies. Furthermore, the cylinders were on the inside of the bogies, but this was also a compound engine. Due to the arrangement of the cylinders, shorter tubes were sufficient. Otherwise, the IV K shared some assemblies with the III K, which is partly recognizable. The model was immediately convincing, which is why production ran from 1892 to 1921. It was used on all narrow-gauge lines in the Saxon network.
After two locomotives were lost during World War I and three more had to be handed over to Poland, the Reichsbahn took over the rest as class 9951-60. There they also came to the Rügen Light Railway and the Prignitz Light Railway.
After a few units had already been taken out of service in the meantime, another 57 units came to the Reichsbahn of the GDR. There the plan was to replace them in the 1960s with the newly developed diesel locomotives V 3648. However, since the axle loads on these were far above the permitted level and they were therefore not produced in series, the steam locomotives had to remain in use. Only the oldest locomotives were retired during this time. In the period that followed, all remaining locomotives received a thorough modernization, which included, among other things, a new, welded boiler and a welded frame. So it turned out that after the German reunification there were still 13 units in active service. After two of them had been sold, Deutsche Bahn AG took over eleven more in 1994. However, these were no longer used as planned.
