<P> 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 . </P> <P> 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 . </P> <P> 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 . </P> <P> 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 . </P>

When was the first transatlantic telephone cable service opened