John Pender - Early Submarine Cables

Early Submarine Cables

The first working submarine cable had been laid in 1851 between Dover and Calais. Its design formed the basis of future cables: a copper conductor, the cable’s core, was insulated with gutta-percha, a type of latex from Malaya which had been found preferable to India rubber for under-water use. The cable was armoured with iron wire, thicker at the shore ends where extra protection from anchors and tidal chafing was needed. Although this basic technology was in place, there was a world of difference between a cross-Channel line of less than twenty-five miles and a cable capable of spanning the Atlantic, crossing the 1,660 nautical miles (3,070 km) between Valentia, on the west coast of Ireland, and Newfoundland in depths of up to two miles (3 km). There were difficulties of scale, and also of electrical management. In long submarine cables, received signals were extremely feeble, as there was no way of amplifying or relaying them in mid-ocean. In 1858, in Newfoundland, using the first Atlantic Cable, it was taking hours and hours to send only a few words, with repeats necessary to try to interpret the weak signals that had to be detected with a candlelit mirror galvanometer on which earth currents registered higher than the actual signals. Three operators at a time had to stand and watch the beam trace on a wall at Newfoundland and make a majority guess about what the intended character was that was coming in.

The original sending voltage applied to the first Atlantic cable in 1858 had been about 600 volts. The British physician, Dr. Whitehouse, made one of the classic mistakes that is still today being made by telecommunications users, when the signals didn't get through, he raised the voltage. Lord Kelvin, the physicist director of the Atlantic Telegraph Company, had reservations, but he was overridden by the non-technical "chief electrician," Dr. Whitehouse. Whitehouse cobbled together apparatus to raise the sending voltage to about 2,000 volts, and the cable's insulation failed and blew apart. After only three months of use and a total of 732 messages, the first cable across the Atlantic Ocean went dead, apparently forever; and with thousands of investors losing their money 'in the sea.'

The Telegraph Construction and Maintenance Company 'Telcon' came up with an improved cable design and built a new cable that was three times the diameter of the failed 1858 cable and weighed in at 9,000 tons in one 2,300-mile (3,700 km) piece. To handle this huge weight of copper and iron, Telegraph Construction and Maintenance Company had to purchase the largest ship in the world at the time, a ship sailors regarded as jinxed, the 700-foot-long (210 m) cargo ship originally named Leviathan, renamed it Great Eastern and fitted it out to be a cable ship.