Transatlantic telecommunications cable

A transatlantic telecommunications cable is a submarine communications cable connecting one side of the Atlantic Ocean to the other. In the 19th and early 20th centuries each cable was a single wire. After mid-century coaxial cable came into use, with amplifiers. Late in the century, all used optical fiber, and most now use optical amplifiers.

When the first transatlantic telegraph cable was laid in 1858 by businessman Cyrus West Field, it operated for only three weeks; subsequent attempts in 1865 and 1866 were more successful. Although a telephone cable was discussed starting in the 1920s, to be practical it needed a number of technological advances which did not arrive until the 1940s. Starting in 1927, transatlantic telephone service was radio-based.

TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. It was laid between Gallanach Bay, near Oban, Scotland and Clarenville, Newfoundland between 1955 and 1956 by the cable ship Monarch. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels. In the first 24 hours of public service there were 588 London–U.S. calls and 119 from London to Canada. The capacity of the cable was soon increased to 48 channels. 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 was finally retired in 1978. Later coaxial cables, installed through the 1970s, used transistors and had higher bandwidth. The Moscow–Washington hotline was initially connected through this system.

All cables presently in service use fiber optic technology. Many cables terminate in Newfoundland and Ireland, which lie on the great circle route (the shortest route) from London, UK to New York City, USA.

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