When the 2-4-2T tank locomotives in use on the commuter lines around Copenhagen were not powerful enough anymore, the DSB ordered Borsig to design a more powerful locomotive. To increase pulling power, the SII received a third driving axle and three cylinders, along with a two-axle trailing bogie to carry more supplies. Mainly designed for passenger traffic, it was also to be used for freight trains when needed.
Only the first two were built in Germany by Borsig, 18 more came from Frichs in Denmark. They were rated for 350-tonne passenger trains at 85 km/h, or for 700-tonne freight trains. In the thirties, the locomotives got condensers for use in tunnels in Copenhagen. In the same decade, they got smoke deflectors to increase forward view. They were withdrawn between 1961 and 1970 and today, two are still existing.