The "Rhineland Cable" was Germany’s first long-distance telephone cable. From 1921 onward, the 600-kilometer line linked Berlin with the industrial region of Rhineland-Westphalia. The first segment, from Berlin to Magdeburg, went into service early in November 1913. The cable itself – called at the time an "exemplary product of German telephone technology" – was supplied by Siemens & Halske.
Sights set on "interurban telephony" – Preparatory work begins
Until 1912, almost every long-distance telephone line in Germany was strung overhead. But "interurban telephony" – as it was called in the day – was highly prone to malfunctions. Extreme weather in the winter of 1909, with freezing snow and violent storms, knocked out almost all telecommunications connections on the Berlin-Hannover segment, along with many lines in Northwestern Germany.
Large portions of telecommunications traffic coming out of or through Berlin were out of service for weeks. The Rhineland-Westphalian industrial region was especially hard hit.
It was an intolerable situation. So the Reichspost decided to replace the existing network of overhead lines with more expensive but more reliable underground cables, and planned on an eventual expansion to a widespread long-distance cable network. Yet experience with such long telecommunications cables was still so limited that the idea of a German long-distance network – still less a European one – was audacious indeed.
Around 1900, Siemens & Halske had correctly recognized how much potential the loading coil developed by Michael Pupin held for the technological development of long-distance telephony; the company acquired the German rights to his invention. Extensive research and testing followed until the “pupinization” technique was ready for use on long-distance phone lines. By 1910, theoretical work had advanced to the point that long-distance cables 1,000 kilometers long seemed feasible. Now work could start on the practical groundwork for building the “Rhineland Cable.”
Extension in two stages – first from Berlin to Hanover, then on to Cologne
In the summer of 1912, Siemens & Halske got the order to "deliver the Berlin–Magdeburg telephone cable, including Pupin coils and other accessories, and to perform the work to establish the cable connection." The order marked the beginning of the European telephone cable network.
The telephone cable was produced by Siemens-Schuckertwerke’s Gartenfeld cable plant; it consisted of 52 two-wire lines, 2 or 3 millimeters in diameter, and had a loading coil every 1,700 meters. Since the cable was pulled through cement pipe in trenches, no further protection from chemical or mechanical stresses was needed. The stranded copper lines were simply protected from moisture with a lead sheathing.
The telephone cable was laid in 170-meter segments, starting late in the autumn of 1912. Work began in Brandenburg an der Havel, and first ran towards Berlin. Once the capital had been connected to the line, installation continued westward from Brandenburg. In August 1913, the 150-kilometer connection between Berlin and Magdeburg was finished; the line went into service in early November. By the next year the telephone cable had already reached Hannover. But then World War I halted any further extensions. Work would not resume until the spring of 1920.
The Rhineland Cable would stretch for more than 600 kilometers in all. The final section, between Dortmund and Cologne, went into service in 1922, using cable supplied by Felten & Guilleaume Carlswerk AG (F&G), based in Cologne-Mülheim. The loading coils were supplied by Siemens & Halske. The two cable manufacturers had already joined forces with Deutsche Reichspost and AEG a year earlier to establish the Deutsche Fernkabel Gesellschaft (DFKG) – a joint venture to standardize the expansion of the German long-distance telephone network.