The BB II series locomotives were Mallet steam locomotives of the Bavarian State Railway. Mallet locomotives are a special type of steam locomotive developed by the Swiss engineer A. Mallet in 1884. This design has two independent running gears, each with its own drive. The rear running gear is firmly connected to the locomotive frame. The front running gear, on the other hand, is movably connected to the locomotive via an extended Bissel truck. Characteristic of the Mallet design is also the way the steam engines worked with compound steam system, whereby the rear cylinders were built as high-pressure and the front cylinders as low-pressure cylinders. The steam was first fed into the high-pressure cylinders and then into the low-pressure cylinders. The most famous German locomotive of this type is the Bavarian Gt 2×4/4 from 1913. The US series 4000 (“Big Boy”) of the Union Pacific Railroad (UP), can be seen as a similar design, as it was also an articulated locomotive, however, this was not a compound locomotive, as all steam cylinders were supplied directly from the boiler.(“simple articulated”).

The BB II series locomotives were specially developed for the Bavarian secondary lines with tight curve radii. Although the Deutsche Reichsbahn took over all vehicles in 1925 as class 98.7, almost all of them were scrapped or sold as factory locomotives in the 1930s due to their poor running characteristics.

Our locomotive was built in 1903 and entered service under the number 2527. In 1923 it was taken over by the Reichsbahn as 98 727 and sold to Südzucker-AG, Regensburg in 1942. There she was given the number 4 and the nickname “Zuckersusi” and received a new boiler in 1958. In 1972 it was donated to our museum and is being extensively repaired after a switching accident.