The D-trains were in service between 1920 and 1939. They rode mainly in the middle-distance services. In constrast with the FD-trains who rode in the long-distance services.
D-trains consisted of coaches first, second and third class and eventually a luggage or postal coach. The coaches of D-trains were not always the newest coaches of the DRG. In the beginning they were mainy old former state railway coaches who had their service in D-trains. This were mainly Prussian, Bavarian and Württemberg coaches. After 1928 when the second generation of standard design coaches arrived, these coaches were used for FD-trains, so the first generation (which was built between 1921 and 1926) was going into service in D-trains. This repeated itself when the skirted coaches were introduced, these were taken into service in FD-trains and coaches of the second generation could be seen more and more in D-trains too. Well this was not so strictly as described above, but between 1928 and 1937 they were made so much express train coaches that in for example 1935 D-trains and FD-trains were made use of the same coaches. This was the same when there came more and more skirted coaches into service.
The same was true for the locomotives, in the beginning mostly former state railway locomotives were used for D-trains, these were locomotives from type BR 11 upto 19, see also locomotives epoch II. Which locomotive was used depended on in which former state the particular D-train operated, so a D-train in Bavarian was pulled by a Bavarian locomotive. When there were built more and more standard design locomotives, these were firstly taken into service in FD-trains and later in D-trains.
The average speed of the D-trains was 100-120 km/h. During the DRG era there were many D-trains in service. On many routes in Germany. A couple of D-trains was in service on international routes.