Revision as of 18:10, 10 March 2010
Author: Bernard Finn
Communications cables under the seas have played a pivotal role in binding the world together—economically, politically and culturally—in ways that have been both beneficial and detrimental (or, one might say, stabilizing and destabilizing). Technical developments have taken the cables through three distinct eras: telegraphy with single-conductor copper wires, beginning in the 1850s; telephony by means of coaxial cables with repeaters, beginning in the 1950s; and data transmission through optical fibers, beginning in the 1980s.
|1847||John and Jacob Brett suggest trans-Atlantic cable|
|1850||First cable across English Channel, worked briefly|
|1858||First cable across Atlantic, failure within a month|
|1861||British Parliamentary Commission report on submarine telegraph cables|
|1864||Successful Persian Gulf cable to Karachi, following Commission recommendations|
|1866||First successful Atlantic cable, laid by Great Eastern|
|1867||Siphon recorder introduced|
|1873||Duplex introduced in Atlantic cables|
|1901||Pacific cable from Canada to Australia and New Zealand|
|1924||First magnetically-loaded Atlantic cable|
|1958||First trans-Atlantic telephone cable, coaxial with repeaters|
|1965||First transistorized Atlantic telephone cable|
|1970||Communications–grade optical fiber developed at Corning|
|1980||Commitment to single-mode fiber transmission for TAT-8|
|1984||Fiber-optic cable to Isle of Wight, first to carry regular traffic|
|1987||Report of erbium-doped fiber amplifier|
|1988||First trans-Atlantic fiber optic cable|
|1996||Optical amplifier introduced in Atlantic cable (TAT-12)|
|1998||First long-distance cables with wave-length division multiplexing|
The importance that society grants to real-time long-distance communications can be seen in particularly dramatic fashion by a consideration of the history of underseas communications cables. They appeared in three distinct forms: the gutta-percha insulated copper-wire telegraph cables that broke onto the scene in the 1850s, the coaxial telephone cables (with repeaters) that appeared a century later, and the fiber-optic data-transmission cables that first were used in ocean-traversing routes in the 1980s. Public drama typically occurred in the mechanical processes of manufacturing and laying the cables; but for the electricians (later called electrical engineers) comparable hand-wringing events took place in the formal or improvised laboratories where electrical (and still later electro-optical) problems were contemplated and solved. This essay will consider technical achievements associated with the development of these cables, together with a briefer consideration of their consequences for society.
A common characteristic of the three major advances in the history of submarine cables is that they have been demand driven. Indeed, the need for communications has been felt so strongly that new ventures were undertaken as soon as or even before the underlying technology was available. Indeed, the first land lines had barely been laid when, in 1845, John and Jacob Brett proposed that an insulated cable be laid across the English Channel. At the same time they suggested that a considerably longer line be stretched across the Atlantic Ocean.
Stage I: Telegraph cables
There were four critical technical impediments to the realization of this dream, all except one of which were solved in the 1840s. The first was a proper insulating material, pliable enough to be extruded efficiently around the conducting wire yet firm enough to withstand the rigors associated with being laid on the ocean floor. Just such a material—gutta percha, the sap from a tree available in and around the Malay peninsula—was introduced to Britain in 1843 and found to be an excellent insulator by Michael Faraday (and in Germany by Werner Siemens). It became plastic at temperatures of about 50 degrees C and could be molded into any shape desired; it would keep this shape when it was cooled to room temperature where it became rigid, but still flexible enough to bend with the coiled cable.
Second was the technique of manufacturing iron-wire rope, deemed necessary for protecting the insulated cable and giving it strength. An Englishman, Andrew Smith, developed a procedure for manufacturing wire rope, using the traditional rope-walking method, in the 1830s. Early in the following decade Robert Newall, also English, devised a machine to do the same thing in a factory.
Third was the availability of steamships, which could lay the cable along a predetermined line. The steamship as an invention is generally attributed to Robert Fulton earlier in the century, and by the 1840s a few were worthy of open-water use. But the need was for vessels large enough to carry a cable that would stretch across the Atlantic. In fact, none had been built as the decade of the fifties opened, and only a few capable of carrying half the length. The British and American governments gave the telegraph promoters the use of two naval steamships: the British Agamemnon (1852) and the American Niagara (whose first voyage was for the cable enterprise in 1857).
Finally there was the need for an instrument that could receive an unamplified signal through almost 2000 miles of wire, together with the concomitant understanding that the signal would be severely distorted because of the capacitance effect of the surrounding water. Nothing like that was available in the 1840s; both would be supplied by William Thomson as on-the-job exercises working as a consultant to the first Atlantic cable venture.
The Bretts laid a cable across the Channel in 1850 which transmitted a few words before it broke; they were successful the next year. More followed, including several (largely successful) attempts in the deeper waters of the Mediterranean, the North Sea, and the Baltic. Most of the laying and manufacturing was done by the British, because of that country’s interest in supporting sea routes (mentioned above) and its monopoly on the supply of gutta percha.
In 1855 Cyrus Field, an American businessman who had made a modest fortune in the wholesale paper business, assumed responsibility for extending a land line to St. John’s, Newfoundland, the main economic value of which was to receive messages from (or deliver them to) ships plying the route between the US and Britain, thus cutting about two days from the delivery time. From the outset Field realized the value of continuing an underwater line eastward. With no technical knowledge of his own, and very little added from consultants, he plunged ahead. What he did have in abundance was the ability to persuade others of the merits of his cause, together with what seemed to be an inexhaustible source of energy. He raised enough money from his New York acquaintances to complete the Newfoundland line, then turned to the British—most particularly the bankers and merchants of Manchester, Liverpool and London.
In what seems an incredibly short period of time (which afforded little opportunity for consideration of possible technical difficulties) a company was formed and 2500 miles of cable was manufactured. Over 300 miles were laid before a break forced a halt to that year’s endeavors.
With more cable, a new attempt was made in 1858. This time the ships met in mid-ocean, having survived one of the worst storms in the North Atlantic on record After three cable breaks (the last after 200 miles had been laid), and with barely enough left, a final laying went flawlessly and an intact cable was in place on August 5.
Success, however, was short-lived. The official electrician, E.O.W. Whitehouse, used pulses in excess of 2000 volts in an attempt to activate standard Morse receivers. The consequence was a failure in the cable insulation and within a month the line was pronounced dead. Fortunately, Thomson had constructed an alternative detector, a “mirror galvanometer.” A small mirror, with magnets glued to its back, was suspended at the center of a coil of wire. An input of only a few volts, when fed through the coil, caused the mirror to twist slightly. This motion was easily detected by viewing the image of a reflected beam of light. A few tests with this instrument before the 1858 cable ceased operation proved its worth.
A Parliamentary committee investigated the causes of this failure and that of a similar cable laid down the Red Sea and across to India the following year. The report, issued in 1861, concluded that, although several mistakes were made, underlying technologies and procedures were sound. In 1864 the India promoters laid a new flawless (but somewhat less ambitious) cable from the head of the Persian Gulf to Karachi. The indefatigable Field returned to London to spearhead the creation of the Atlantic Telegraph Company that, with British capital and technology, in 1865 would lay a cable two-thirds of the way across the Atlantic before it broke (and could not be retrieved with grappling equipment at hand). The Anglo-American Telegraph Company was then formed to lay a new cable, and complete the 1865 cable, in 1866. For both of these efforts the promoters had the advantage of being able to load the full length on the Great Eastern, which had been launched in1858 as an ill-conceived passenger liner for the route to Australia but found a new and profitable life as a cable ship.
These first cables quickly spawned more. By 1873 they reached as far as Singapore, Hong Kong, and Sydney. The islands of the Caribbean were linked together and connected to the mainland; as were the islands of the eastern Mediterranean and those of the East Indies. The Pacific Ocean was crossed in 1901 (by the British) and a second time in 1903 (by the Americans). By way of contrast, the Atlantic embraced a dozen active cables at the turn of the century, and twenty-one in the late 1920s.
Operators using Thomson’s mirror galvanometer initially were able to receive three words per minute; with practice they raised this to about seventeen. But no permanent record was produced. Thomson’s response was to suspend a coil between the poles of a magnet. Threads from the coil were attached to a slender glass tube that had one end in ink and the other facing a moving paper tape. To reduce friction, the ink was electrified and deposited on the paper in spurts. The coil, which was part of the telegraph circuit, twisted back and forth in response to the signals, and a wavy line appeared on the tape. This “siphon recorder” was initially capable of receiving a dozen words per minute, a number that increased by a factor of three or more by the end of the century. Introduced in 1867, it remained the principal receiving instrument on long submarine lines for half a century. The mirror galvanometer was used as a sensitive test instrument into the 1950s.
Although the telegraph cable industry proved to be fairly conservative, some innovations were adopted over its hundred years of service. Duplex techniques (the ability to send two messages at the same time, in opposite directions) were adapted from land line practice by J. B. Stearns and first applied to an Atlantic cable in 1873. Modifications of the siphon recorder were introduced in the second decade of the twentieth century: the twisting coil, instead of being attached to a siphon was connected by threads to various forms of an electrical relay.
For a half century there were no consequential changes in the design of the cables, except for a sheathing of brass tape applied around the gutta percha to protect it from the toredo, a boring insect common to warm waters. In the 1920s the effects of capacitance were partially offset by “loading” three new cables (in 1924, 1926 and 1928) with wrappings of the just-discovered magnetic materials permalloy or mu-metal. To take advantage of the increased capability, a system of time-division multiplex was introduced. Concentric bands of short conducting segments on a rotating disc made contact through brushes with different message transmissions. The segments were spaced so that only a single band made contact at any moment in time. The disc moved fast enough so that enough “samples” were taken from each message for its basic shape of positive and negative pulses to be preserved. A similar synchronized rotating disc at the other end of the cable separated out the individual messages. Up to eight separate channels could be used (each duplexed) at speeds of up to 60 words per minute each. Finally, as the end of an era unknowingly approached, in 1951-52 Western Union spliced electronic amplifiers into their non-loaded cables at the edge of the continental shelf (these were bulky devices that could not practically be used in deeper waters).
It is not the purpose of this essay to give a detailed account of the social effects of the telegraph cables, though they touched virtually every aspect of life. In the brief moment when the 1858 cable was thought to be successful a variety of optimistic prophesies were put forward, most particularly that by promoting mutual understanding it would help bring peace to the world. Perhaps it would have been better to say that the cables could be used in the cause of peace, while recognizing that they could equally be used as tools for war. What we know now is that these telegraph cables would be employed extensively by news organizations, financial institutions (by connecting domestic networks they made futures trading possible), government diplomatic departments, shipping companies, and commercial enterprises of all sorts. Operation and maintenance of the cables required international agreements, which led to establishment of the International Telecommunications Union in 1865. Personal use was restricted by the expense, but one can argue that psychologically individuals began to feel more intimately connected to other people and events around the globe.
It must be noted that gutta percha was harvested from a mature tree (25-35 years old), and unlike rubber it did not flow easily, which meant that the tree had to be cut down. At 1½ pounds of refined gutta percha per tree, this meant 200 trees per mile of cable. One reasonable estimate has been made that eventually some 100 million trees were needed to satisfy the needs of the cable industry. A mitigating factor is that towards the end of the nineteenth century both the Dutch and the British established plantations to satisfy at least some of the demand.
In the mid -1920s short-wave wireless technology had advanced to the point where it could consistently undersell the cables, most notably with the advent of powerful vacuum-tube transmitters. This might have signaled the demise of the cables but for two factors: one was privacy (anyone could pick up a wireless signal); the other was reliability (wireless transmissions could be interrupted by adverse conditions in the ionosphere). Governments used this excuse to exert pressure on the companies involved (most of which were privately owned) not to allow the cables to die. In Britain the result was a merger of the Maroni Wireless Telegraph Company and the Eastern and Associated Telegraph Companies in 1929 to form what became Cable and Wireless, Ltd. Although there were merger talks in the United States, in the end there were none and the two technologies co-existed until the war brought on new challenges for both.
Stage 2: Telephone cables
The commercial success of trans-Atlantic wireless telephone service, inaugurated in 1927 by AT&T, encouraged the company to consider the possibility of a wire circuit. By 1929 a decision had been made to proceed. The new line would support a single voice channel and would, in effect, represent a modest improvement on the latest loaded telegraph cable. The Depression and the war intervened, however, and when the question was revisited in the late 1940s technological advances opened up an entirely new possibility.
The main advance was in vacuum tubes. Miniature versions had been developed in the late 1930s and had seen extensive wartime service. They were small enough (less than an inch—or 2.5 cm--in diameter) to be employed in amplifiers that could run through the cable-laying machinery, and rugged enough to survive at least 20 years under water without servicing. A second advance was polyethylene, another development of the thirties and an ideal replacement for (and improvement on) gutta percha. An additional difference from the telegraph cables was use of a coaxial design, eliminating the use of the ocean as an electrical ground and return conductor. The relatively slender amplifier was capable of only one-way operation, so two cables would be needed. Agreement was reached with the British General Post Office (GPO), which had developed larger two-way repeaters for shallow water. The result, in 1956-57, was a two-line trans-Atlantic telephone cable (TAT-1) between Oban, Scotland, and Clarenville, Newfoundland (each line with 51 narrow flexible repeaters, approximately one every 30 miles). An extension in shallow water from Clarenville to Sydney Mines, Nova Scotia was a single line with 14 British repeaters. Most of the cable was manufactured in Britain. It was capable of carrying 36 4-kHz channels, or 48 3-kHz (later expanded to 51). Both the American and British sections were laid by the GPO ship Monarch-4, which had been launched in 1947 and had been designed with the anticipated needs of repeaters in mind.
TAT-1 was an immediate success, and was quickly followed by a similarly-designed TAT- 2 in 1959. An improved design, with a high-tensile steel wire strand at the center replacing outer armoring wires, and two-way repeaters, was first used in CANTAT-1 between Scotland and Newfoundland in 1861. It provided 80 channels. That same year AT&T launched the cableship CS Longlines.. In 1963 it laid a single-line TAT-3 between Tuckerton, NJ, and Widemouth Bay, Cornwall, with repeaters every 20 miles and carrying 128 channels. In 1963 Long lines also laid a cable across the Pacific, from Canada to Australia and New Zealand.
A major advance came when transistors had proven themselves stable enough to be buried at sea, unattended for many years. They were used in TAT-5, between New Jersey and Spain in 1970, with repeaters every 10 miles carrying 845 channels. The ultimate in this upward spiral was achieved by TAT-6 (Rhode Island to France) and TAT-7 (New Jersey to Britain) with repeaters every five miles and over 4000 channels each. Other advances included the use of a plow to bury shallow water sections, a practice later extended to deeper waters as well. It is worth noting that such a plow had been developed for use with telegraph cables in the late 1930s.
Although orbiting communications satellites and the new cables can be seen as responses to the post-war internationalist boom, they also provided unanticipated possibilities that were quickly seized on by society. Satellites, with their television capabilities, were especially important for dissemination of cultural programs and news. The cables, arguably, caused a fundamental shift in the management of long-distance diplomacy and military operations. Even minor details could now be controlled by a central command far from the scene of action. In similar ways, the same was true for businesses. Individuals could but marvel at the ease and low cost of international telephone calls.
The coaxial, repeatered cables were challenged almost immediately by synchronous satellites, which became commercially viable with Intelsat I (“Early Bird”) in 1965. But the costs weren’t all that different, and especially for telephone conversations the cables more than held their own because the time taken for the signal to get up to the satellite and down was a quarter second in each direction and thereby introduced an annoying half-second delay between speaking a word and hearing a response. Also, as in the previous era, cables were more secure. There emerged a rough division in which most of the telephone traffic used cable, television used satellite, and data was split between them.
Stage 3: Fiber optics
Both coaxial cables and satellites were threatened by a new technology called fiber optics. On land, in the 1960s, AT&T was on the verge of deploying a network of microwave–carrying pipes to replace the existing tower-based through-the-air system when it became clear that optical fibers would be cheaper and more flexible. Most important, as forms of electromagnetic radiation light rays surpass microwaves in having a much greater frequency (pulses per second) and thus a much greater information capacity . Critical work was done at Corning Glass Works, where a team was formed in 1967 with the goal of creating a type of glass that would retain at least one percent of light through a kilometer of fiber. This was achieved in 1970. Further advances followed--at Corning and at other laboratories that joined in the quest. By the end of the decade practical optical communications lines were being deployed across the landscape.
There were still significant challenges to be overcome, however, before the underwater coaxial cables would have to surrender their preeminence. Problems were addressed on an international stage, with critical contributions coming from numerous sources, most particularly AT&T, MIT, Nippon Telegraph and Telephone (NTT), GPO, Standard Telephones and Cables. Fibers don’t transmit all wavelengths with equal transparency; any given chemical composition has particular optimal frequency ranges; and lasers, which were used as light sources, have their own special ranges. Getting a match between the two was not important for relatively short land lines, but it was crucial for sending signals through thousands of miles of cables without requiring impractical numbers of amplifiers. Fortuitously, in the mid-1970s J. Jim Hsieh at MIT Lincoln Laboratory developed a laser and Masaru Horiguchi at NTT produced a fiber that had just such a match. As a consequence, in 1978 a commitment was made by AT&T, GPO and Standard Telecommunications Laboratories that TAT-8, scheduled for a decade later, would be fiber-optic and not coaxial. They also decided to use a narrow band of frequencies (single mode), confined by a very slender fibers.
The first submarine fiber cable (five miles with no repeaters) was laid in the English Channel between Portsmouth and the Isle of Wight in 1984. It was followed two years later by a cable across the Channel to Belgium (over 70 miles with three repeaters) which could carry 11,500 telephone circuits on the fiber pairs. TAT-8 went into service in 1988, a three-fiber cable (two operational, one back-up) from the United States to Britain and France via a branch point in the Atlantic. It successfully carried the equivalent of 40,000 telephone conversations.
There was, at the time, no way of amplifying light directly. Instead, a light signal was converted to an electrical signal, which was amplified and turned back to light. This complex arrangement was relieved by the invention of a light amplifier, a laser using glass doped with erbium, by David Payne at the University of Southampton in 1987 and developed separately by Emmanuel Desurvire at Bell Labs. With contributions from several other laboratories, in what continued to be a global effort, practical optical amplifiers were developed with the added revolutionary feature that they could handle several frequencies at the same time. They were applied to TAT-12 in 1996 (which was a US-British-French enterprise), giving it a capability of transmitting five gigabites per second of information over each of two fibers. When combined with TAT-13, it formed a loop structure, with traffic moving in opposite directions over the two cables, thus making it possible to re-route traffic and minimize disruption in the event of damage to one of the fibers.
By the new millennium a network of communications fibers embraced the globe, and competing companies continued to lay the relatively inexpensive cables in response to an expanding market. They were so successful that within a few years supply exceeded demand, and the cost to consumers dropped precipitously. Another consequence was that some companies overextended themselves and were forced into merger or bankruptcy. The situation was not helped as the consequences of a world-wide recession began to be felt in 2008, and at the time of this posting (2010) it is difficult to predict how the interplay between supply and demand will play out. It seems safe to say, however, that optical fibers will reign supreme as conveyors of information for a reasonable number years.
The growth of the fiber network coincided with the rise of the world wide web, making possible the enormous expansion of services that has made the internet of such overwhelming importance to social, political and economic affairs around the globe. It is a history that is still being written.
The author would like to thank members of the STARS Editorial Board for review and constructive criticism of this article, with special thanks to David Hochfelder for helpful comments and suggestions.
References of Historical Significance
References for Further Reading
About the Author(s)
Bernard Finn is curator emeritus at the Smithsonian Institution, where for over forty years he was curator of the historical electrical collections. He developed a special interest in submarine telegraphy, which has been reflected in collecting activity (both objects and documents), publications, exhibitions, and advisory roles.