TAT-1 (Transatlantic No. 1) was the first submarine transatlantic telephone cable system. It was laid between Oban, Scotland and Clarenville, Newfoundland. Two cables were laid between 1955 and 1956 with one cable for each direction. It was inaugurated on September 25, 1956. The cable was able to carry 35 simultaneous telephone calls. A 36th channel was used to carry up to 22 telegraph lines.
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 (about $45 USD, or roughly $550 in 2010 dollars) for three minutes and handling around 300,000 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 1,500 nautical miles (2,800 km) 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 (69 km) intervals - a total of 51 repeaters in the central section. The armored cables were manufactured southeast of London, at a factory in Erith, Kent, owned by Submarine Cables Ltd. (owned jointly by Siemens Brothers & Co, 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 Her Majesty's Telegraph Ship (cable ship) Monarch. At the land-end in Gallanach Bay near Oban, Scotland, the cable was connected to coaxial (and then 24-circuit carrier lines) carrying the transatlantic circuits via Glasgow and Inverness to the International Exchange at Faraday Building in London. At the cable landing point in Newfoundland the cable joined at Clarenville, then crossed the 300-mile (480 km) Cabot Strait by another submarine cable to Sydney Mines, 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 original 36 channels were 4 kHz. The increase to 48 channels was accomplished by narrowing the bandwidth to 3 kHz. Later, an additional three channels were added by use of C Carrier equipment. Time-assignment speech interpolation (TASI) was implemented on the TAT-1 cable in June 1960 and effectively increased the cable's capacity from 37 (out of 51 available channels) to 72 speech circuits.
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.
- "Specimen of the first transatlantic telephone cable, 1956". The Science Museum. Retrieved 4 June 2015.
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- Mattingley, F. (January 1957). "Manufacture of Submarine Cable at Ocean Works, Erith". The Post Office Electrical Engineers' Journal 49 (4): 308.
- "Overall Characteristics of a TASI System" (PDF). September 19, 1961. Retrieved 8 October 2014.
- "Milestones:The First Submarine Transatlantic Telephone Cable System (TAT-1), 1956". IEEE Global History Network. IEEE. Retrieved 3 August 2011.
- TAT-1 Opening Ceremony Includes transcript of the official first telephone call over the cable.
- Reminiscences of TAT-1 by Jeremiah Hayes (in .pdf format)
- 50th Anniversary of laying TAT-1 BBC News
- 50th Anniversary of laying TAT-1 Scotsman