The class 270 of the Reichsbahn and later 485 of the Deutsche Bahn designates EMUs for the Berlin S-Bahn, which have been developed since the late seventies. They were ordered because of the problem that the fleet at that time was completely pre-war and a new model presented in 1959 had not gone into series production.

During development, care was taken to ensure that the external dimensions of the new cars corresponded as closely as possible to those of the old ones. This ensured that they could be dispatched in the same way in the company and that nothing had to be changed in the workshops. On the technical side, on the other hand, new achievements were used. Energy consumption was reduced by around 30 percent, primarily through lightweight construction and an electric regenerative brake. 

Although the prototype was presented at the Leipzig Spring Fair in 1980, the pilot series was not built until 1987. Series production took place from 1990 to 1992 with each 158 power cars and trailers instead of the originally planned 300 units. Instead, more examples of the West Berlin class 480 were procured. Nevertheless, the series was still not dispensable after 2010, partly due to failures and problems with newer series.

As a result, some that had already been parked were later reactivated and from 2015 there were even modernization measures. The latter included conversions in the area of radio, passenger information system and drive and brake equipment and should ensure that the vehicles can be used until at least 2023. Due to the additional equipment, the weight increased on individual bogies, which required a conversion of the service compartments. Nevertheless, due to the lack of the new train control system, the trains have not been able to be used on the Stadtbahn since 2018. This was an additional reason why general inspections have not been carried out since 2020 and the trains are to be parked when the deadline expires.

A further development was the Duo-S-Bahn, which was also equipped with underfloor diesel generators to bridge sections without conductor rails. However, since use on main routes together with faster trains would have been difficult and there was no further need, this model did not go into series production.