The ET 165 is a class of pre-war railcars for the Berlin S-Bahn, which to this day has the highest number of railcars in Germany. They were built in a short period of time between 1928 and 1931 and were in daily use until 1997.
The vehicle concept envisaged that two cars, which always remain coupled together in everyday life, form a so-called quarter train and up to four of these quarter trains are connected depending on demand. Since each part had its own power train, the same power-to-weight ratio was available for every train length. Each quarter train consisted of one motor car and one control car. Later, the control cars were replaced by trailers and all existing control cars were converted to trailers. The power supply via third rail had the advantage that the vehicles were supplied directly with 750 volts DC and no longer needed their own transformers. Each of the two bogies of the motor car had two nose-suspended motors connected in series, which were each operated with 375 volts. Furthermore, weight was saved by making the load-bearing parts in a new alloy and the cars were around seven to nine tonnes lighter than their predecessors.
638 motor cars, 465 control cars and 173 trailers were built, which quickly dominated traffic on the Berlin S-Bahn. There were still a few teething problems, such as the wooden doors, which often warped, and the bogies needed improvement, but these were gradually fixed. As a result of the war, some vehicles came to various eastern countries, where some of them remained in use for a long time.
In the post-war period, traffic in both parts of Berlin was rebuilt with these vehicles. In West Berlin in particular, their number fell continuously in the 1970s and 1980s, as large numbers of new vehicles were procured and the existing vehicles were only modernized to a limited extent. Nevertheless, some were still in service after the takeover by Deutsche Bahn AG and were used until 1997 as the class 475/875 together with their sisters from East Berlin.
In the east, a large part of the vehicles had been reconstructed from 1979, as had already happened with the successor class. In addition to the interior design, the front sides were also modernized. The vehicles converted in this way were renamed from class 275 to 2761 and were only retired in 1997 together with the West Berlin vehicles.