The D IX was built between 1888 and 1899 by Maffei for the Bavarian State Railways, mainly to be used in front of light passenger trains on the Reichenhall-Freilassing-Salzburg route.
The chassis of the engines consisted of two coupled axles with wheels with a diameter of 1,340 mm and a fixed leading axle. Due to the relatively large wheelbase of the driving axles, which were also fixed, there was less than satisfactory running characteristics in curves and increased wear. The two cylinders were located in front of the leading axle, which turned out to be not the most advantageous layout in terms of vibrations and maintenance.
The maximum speed was 65 km/h, which was sufficient on secondary routes at the time. On the level, the locomotives could be fully utilized with trains up to a maximum of 170 tonnes, but at 2 percent only 20 km/h with a train load of 95 tonnes were possible. In view of the increasingly heavier trains, this performance was soon no longer sufficient, and so the D IX were replaced by six-coupled engines of the D VIII type.
They found their new field of application in the suburban lines of Munich, Nuremberg and Augsburg, where almost all of the 55 locomotives made remained in use until after the First World War. They were assigned to class 7071 from 1925, when their ranks had already thinned out. All the rest were decommissioned by 1932.