The S3 was one of the first six services of the Rhine-Main S-Bahn system. In a prior test operation it ran between Frankfurt-Höchst and Frankfurt Central Station. The service was then called R3 where the letter "R" stands for regional. After the opening of the Frankfurt Citytunnel the service was renamed to S3 and extended to the new Hauptwache underground station. Further extensions of the tunnel followed in 1983 (Konstablerwache) and 1990 (Ostendstraße and Lokalbahnhof) so that the Südbahnhof (South station) became the service's eastern terminal.