The St. Gallisch-Appenzellische Eisenbahn [de] (SGAE) had opened its line between Winterthur and St. Gallen between October 1855 and March 1856.

[citation needed] The SGAE merged with the Glatthalbahn in 1857 to form the United Swiss Railways, which owned the line through the end of the century.

[4] Electrical operations commenced on 15 May 1927 at 15,000 Volt 16 ⅔ Hz between Winterthur and Rorschach.

The new section was put into operation with the 1466 metre-long, double-track Rosenberg Tunnel on 1 April 1912.

The railway line crosses an area affected by earth creepage in the Steinach valley in Galgentobel.

Thus, later there was an isolated section of double track between Mörschwil and the newly created operations yard at Engwil.

This situation continued until 2008, when the section between Mörschwil and Goldach was rebuilt as double track.