The Zwillinge (“twins”) were small tank locomotives that were built for the Bavarian and Prussian Heeresfeldbahnen (military field railways). What was special was that, in normal service, two technically identical, otherwise independent locomotives were coupled together back to back. The cab roofs were of different heights to allow for overlap. When the locomotives were used individually, they were also referred to as “Illing”. If necessary, an additional tender was attached.

More than 50 pairs were delivered to the Swakopmund-Windhuk state railway in German South West Africa, where the field railway construction command built a 600 mm gauge line through the Namib Desert. The Japanese Army Field Railway also received a total of 89 pairs in 1905 and 1906. Some Zwillinge from German South West Africa were also sold to Japan when the gauge was changed to Cape Gauge. Only a few examples were used for civilian purposes. The successor was the Brigadelokomotive, which, with four driving axles, was more powerful than a single Illing.