What is Transatlantic communications cable?

Most such cables follow the great circle route from London to New York City because of the high-speed requirements of international financial transactions. Financial trading firms spend billions of dollars annually to get an edge on trading.

This route provides convenient well-supported landings near Halifax (or Moncton), St. John's, Iceland (or Belfast) and Dublin. Many cables are monitored and controlled from such central locations rather than from the endpoints, for quicker response to problems, and because it's cheaper to hire qualified people in these less expensive locations. Iceland, furthermore, has great advantages for communications companies as they are effectively immune from defamation lawsuits for disseminating any adverse information about public events or companies or figures, which is a key driver of day trading and arbitrage activity. Such intermediary points on the great circle route are expected to play an increasingly prominent role in these activities, if only because trading signals originating there reach both London and New York faster than any signal originating in one centre trying to reach the other.

When the first transatlantic telegraph cable was laid in 1858 by businessman Cyrus West Field, it operated for only a month; 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. TAT-1 was finally retired in 1978.

There have been a succession of newer transatlantic cable systems. All recent systems have used fiber optic transmission, and a self-healing ring topology. Late in the 20th century, communications satellites lost most of their North Atlantic telephone traffic to these low cost, high capacity, low latency cables. This advantage only increases over time as tighter cables provide higher speed - the 2012 generation of cables drop the transatlantic latency to under 60 milliseconds, according to Hibernia Atlantic, deploying such a cable that year.