Transatlantic Telecommunication Via Voice

World’s first purpose-built Cable Layer Ship
Silvertown, 1901

On September 25, 1956 the world’s first submarine transatlantic cable for telephony TAT-1 (Transatlantic No. 1) was inaugurated. It was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland between 1955 and 1956 by the cable ship Monarch. You might wonder that is was only possible to route a call between Europe and the United States before the mid 1950s, well at least by cable. Don’t you at least remember some old black and white movies, where they claimed to make a phone call across the Atlantic? Well you’re right.

But all transatlantic calls prior to 1956 were relayed by radio transmission, which was expensive, unreliable, and often disturbed be interfering noise. But, now you might argue that there has been a transatlantic cable almost 100 years earlier. And again you are right. But, this first transatlantic telegraph cable laid in 1858 by businessman Cyrus West Field was only meant to transmit Morse signals and not such complex signals as the human voice.

The famous cable we are talking about here had 36 voice channels and 51 amplifiers located at a distance of 70 km. In the first 24 hours of use, over 700 calls were performed wherefore the capacity was soon increased.

Even though, the TAT-1 was a great success, it was just the first of a whole series. The system was shut down in 1978 and followed by the TAT-2. The successor of the TAT-1 was upgraded by the capacity as well as a new method called ‘time-assigned speech interpolation’.  This means that channels are only assigned when the caller is actually speaking. More TAT versions later followed, increasing the number of channels making it possible to include more and more countries for faster and safer communications. The current generation of transatlantic communication cables, TAT-14, of course offers digital connectivity based on fiber optics enabling bandwidths of up to 3.2 Tbps (only in theory, in practise 1.87 Tbps can be reached).

At yovisto you might watch an old video from AT&T Archives about long line telephone communications and the technology of submarine telecommunication cables.

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