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TAT-1 (Transatlantic No. 1) was the first submarine transatlantic telephone cable system. It was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland between 1955 and 1956. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.

While the first transatlantic telegraph cable had been laid in 1858 (see Cyrus Field), it had only operated for a month. Attempts in 1865 and 1866 were more successful but although a telephone cable was discussed from the 1920s it needed a number of technological advances that did not arrive until the 1940s to be practical. Until TAT-1 the transatlantic telephone service was radio-based, started in 1927 it cost 9 for three minutes and took around 2000 calls a year.

The developments that made TAT-1 possible were coaxial cable, polyethylene insulation (replacing gutta percha), very reliable vacuum tubes for the submerged repeaters and a general improvement in carrier equipment.

The agreement to make the connection was announced by the Postmaster General on December 1 1953. The project was a joint concern between the General Post Office (UK), American Telegraph and Telephone and the Canadian Overseas Telecommunications Corporation. The share split in the scheme was 40% UK, 50% US and 10% Canada. The total cost was 120 million.

There were to be two main cables, one for each direction of transmission. Each cable was laid in three sections, two shallow water sections and one 1500(?) mile central section. The repeaters were designed by Bell Laboratories to be flexible and were inserted into the cable at 37 nm intervals, there were 51 repeaters in the central section. The armoured cable was manufactured in south east London, England at a factory in Erith, Kent.

The cables were laid over the summers of 1955 and 1956, with the majority of the work done by the cableship Monarch. At the land-end in Scotland the cable joined to an coaxial line carrying 900 inland and transatlantic circuits to the International Exchange in London. At the Newfoundland end the cable joined at Clarenville, then crossed the 300-mile Cabot Strait by another submarine cable to Nova Scotia. From there the communications traffic was routed to the US border by a microwave radio link and in New Brunswick, Maine, the route joined the main US network and branched to Montreal to connect with the Canadian network.

Opened on September 25 1956 in the first 24 hours of public service there were 588 London-US calls and 119 from London to Canada. The capacity of the cable was soon increased to 48 channels.

After the success of TAT-1 there were a number of other TAT cables and TAT-1 was retired in 1978

See the transatlantic telephone cable article for more information on the history of transatlantic cables.

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