The class 420 trainsets are electric multiple units formed of three cars for 'S-Bahn' commuter services. 480 units were built in eight series in the years 1969 to 1997. They were in operation in the suburban railway networks of Frankfurt am Main, Stuttgart, Munich and Rhine-Ruhr. In the meantime, most of the trainsets were replaced by new class 423 and 422 (Rhine-Ruhr) resp. 430 (Frankfurt, Stuttgart) vehicles.