coaxial line


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.


The first transatlantic telegraph cable had been laid in 1858 (see Cyrus West Field). It only operated for a month, but was replaced with a successful connection in 1866. A radio-based transatlantic telephone service was started in 1927, charging £9 (or roughly $45 USD) for three minutes and handling around 2000 calls a year. Although a telephone cable was discussed at that time, it was not practical until a number of technological advances arrived in the 1940s.

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. Transistors were not used, being a recent invention of unknown longevity.

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

There were to be two main cables, one for each direction of transmission. Each cable was produced and laid in three sections, two shallow-water armored sections, and one continuous central section 1500 nautical miles long. The electronic repeaters were designed by the Bell Telephone Laboratories of the United States and they were flexible and were inserted into the cable at 37 nautical mile intervals - a total of 51 repeaters in the central section. The armored cables were manufactured in southeast London at a factory in Erith, Kent, owned by Submarine Cables Ltd. (owned jointly by Siemens Brothers & Company, Ltd, and The Telegraph Construction & Maintenance Company, Ltd).

The cables were laid over the summers of 1955 and 1956, with the majority of the work done by the cable ship Monarch. At the land-end in Gallanach Bay near Oban, Scotland, the cable joined to a coaxial line carrying 900 inland and transatlantic circuits to the International Exchange in London. At the cable landing point in Newfoundland 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 relay link, and in Brunswick, Maine the route joined the main US network and branched to Montreal to connect with the Canadian network.

Opened on September 25 1956, TAT-1 carried 588 London-US calls and 119 London-Canada calls in the first 24 hours of public service. The capacity of the cable was soon increased to 48 channels.

The original 36 channels were 4 kHz. The increase to 48 channels was accomplished by narrowing the bandwidth to 3 kHz. Later, an additional 3 channels were added by use of C Carrier equipment. Time-assignment speech interpolation brought a further increase in the late 1960s.

TAT-1 carried the Moscow-Washington hotline between the American and Soviet heads of state.

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

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