The class VI K referred to ten-coupled tank locomotives with a gauge of 750 mm, which were originally developed for the army administration during the First World War. A distinction must be made between the 15 locomotives built during the war and the 47 replica and slightly modified examples from the 1920s.

In order to achieve a good ability to negotiate the narrow curve radii of the narrow-gauge railways despite the five coupled axles, the running gear was designed according to the Gölsdorf system with the first, third and fifth axles being laterally movable. The engine was designed with superheated steam created by a smoke tube superheater, and the newer engines also had a copper firebox. 

From 1925, the Reichsbahn designated the locomotives built in 1918 and 1919 as 99 641 to 99 655. The rest were added between 1923 and 1927 and were given the numbers 99 671 to 99 717. With their new operator, the locomotives were also used outside of Saxony, for example in Württemberg and Austria. Some were even shipped directly to the distant regions from the factory.

After the Second World War they got to both parts of Germany, another one was even used in Czechoslovakia until 1962. The Bundesbahn retired the last VI K in 1967. Since the engines were to be used for a longer period of time on the East German Reichsbahn, either a large-scale overhaul or a complete rebuild took place in the 1960s, depending on the condition of the individual locomotives. While welded boilers, water and coal bunkers were installed in the first of these options, the rebuild almost resembled the building of a new engine. The locomotives were put on new frames and the driver's cabs were renewed.

Three examples still exist today, of which road numbers 99 713 and 99 715 have been preserved in working condition in Saxony and are actually operated. The 99 716 has also been used since 1997 and last drove on the Öchsle in Baden-Württemberg, but is no longer roadworthy today.