During the existence of the Deutsche Reichsbahn-Gesellschaft, there was a large number of developments in the area of railcars and multiple units. While the vehicles from the era of the Länderbahnen (individual state railways in the German states) were mainly built for traffic on branch lines or suburban railways, there were now developments primarily for commuter and intercity traffic. Now only vehicles that were either powered by internal combustion engines or electrically were created.
In the field of internal combustion railcars, initially only small vehicles for branch lines were built in the 1920s, which today would generally be referred to as rail buses. The development of engine technology soon made it possible to build larger and faster railcars for main lines. When considering the possibilities, it became clear that the use of large steam locomotives was hardly economical for very fast passenger transport with low passenger numbers and that express railcars could be the solution.
The rail zeppelin of 1930 was a dead end in development, as an attempt was made to create traction via the air with a propeller. Instead, in the years that followed, different railcars were developed for the speed range between 80 and 160 km/h (50 and 100 mph), most of which had diesel-electric power transmission. Over time, more vehicles with hydraulic power transmission were ready for series production, which, despite their greater complexity, had a weight advantage. The engines were mostly tried to be mounted under the floor in order to be able to use more space for the passenger compartment. A lot of effort was put into their suspension, as the engines were closer to the passenger compartment than on locomotive-hauled trains and the noise and vibrations had to be kept away from the passengers. In addition, as the speed increased, care had to be taken that the engines themselves felt fewer bumps from the rails.
The fastest series-produced multiple units were the “Flying Trains”, which connected the major cities with a maximum operating speed of 160 km/h. Although they were only built in small numbers and, with their limited passenger capacity, could only handle a small part of the traffic between the cities, they were marketed effectively and gained international attention. Some standard railcars were also built for travelling speeds of around 100 km/h, which operated on a large network. With the beginning of the Second World War, series production of the express railcars was discontinued and their further development initially stopped. Despite these circumstances, the production models and some innovative prototypes served as a basis for further developments on both sides of the Iron Curtain after the war.
In the 1920s, in the area of electric multiple units, besides vehicles for suburban traffic there were initially mainly ones for commuter traffic. The ET 85 saw the light of day as a four-axle steam railcar, of which several vehicles were converted to electric power. More railcars were soon built, for example for commuter traffic in the Central German network or in the Giant Mountains, which could also haul multiple passenger cars. It was not until the 1930s that several types of multiple units for intercity traffic were created, which could reach speeds of 120 km/h and were powered by nose-suspended motors.
The three prototypes of the ET 11 were built in 1935 for a planned use of express trains such as the diesel-powered “flying trains”. These 160 km/h two-car railcars were given different types of technical equipment and were successfully tested. Series production of more electric express railcars a larger capacity did not materialize, since at the beginning of the war there was no longer any need for passenger transport at this speed. The vehicles that still existed after the Second World War were indispensable in the years that followed, especially on the Bundesbahn, and were used for a long time. Many sets received new fronts and new multiple units were combined from existing individual cars. Vehicles like the ET 25 or ET 31 were used until the 1980s.