Although the large companies in industry and the mining sector mainly ordered diesel locomotives for shunting and transfer services after the war, steam locomotives continued to be built for these purposes. Since simple locomotives with saturated engines were sufficient here, Krupp included a six-coupled tank locomotive that had already been delivered in 1935 in the post-war program. Since this locomotive was then delivered to a fertilizer factory in Hürth-Knapsack, the type was given the name “Knapsack”.

In terms of size and weight, the locomotives roughly corresponded to the class 89⁰ standard locomotive, in terms of power they were somewhere between its saturated and superheated versions. With a wheel diameter of 1,100 mm, speeds of up to 45 km/h were possible and with an axle load of less than 15 tonnes, it could be used on almost all standard-gauge industrial railways. Of the twelve units sold in Germany, the largest order, five, went to a colliery in Neukirchen-Vluyn. Three more pieces were exported to Turkey.

Today there are still six units, one of which has been in service with the Hespertalbahn since 2000 and was parked at the end of 2016 when the deadline had expired. Currently, the Hespertalbahn states that the locomotive is being refurbished and will undergo a general inspection.

In World War I, the Halberstadt-Blankenburg Railway in the Harz mountains searched for a way to increase freight traffic on their rack lines which had a gradient of up to six percent. So they ordered two heavy 2-10-2T tank locomotives which could operate with adhesion only and so reach higher speeds. For greater safety when running downhill, they got cog wheels for braking which used the existing rack.

The second and fifth driving axles had side play of 30 mm, while the third one had no wheel flanges. To realize a huge power output, the boiler got a huge diameter of 2,000 mm at a tube length of only 3,700 mm. In the result, these two locomotives had no problems at all with the tight curves and could haul 260 tonnes with 12 km/h on six percent.

Two more locomotives were ordered, but without the braking cog wheels since they were found unnecessary after the trials. These had also been removes from the first two. The four got the names “Mammut”, “Wisent”, “Büffel” and “Elch” (mammoth, bison, buffalo and moose), hence the name “Tierklasse” (animal class).

The Reichsbahn numbered them 95 6676 to 95 6679. Since they needed more powerful ten-coupled tank locomotives to replace slow rack locomotives, the Tierklasse was used as an inspiration for the Prussian T 20. In 1949, all came to the East German Reichsbahn, where the boiler of 99 6679 (ex “Elch”) exploded only two years later. Only 95 6676 (ex “Mammut”) is preserved after its 1968 withdrawal and can today be found non-operational at Dresden.

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.