Editing Submarine communications cable (section)

==Early history: telegraph and coaxial cables==
===First successful trials===
After [[William Fothergill Cooke|William Cooke]] and [[Charles Wheatstone]] had introduced their [[Cooke and Wheatstone telegraph|working telegraph]] in 1839, the idea of a submarine line across the Atlantic Ocean began to be thought of as a possible triumph of the future.<ref>{{Cite journal |last=Abildgaard |first=M. S. |date=2022 |title=The question of Icebergs: a cryo-history of Arctic submarine cables |url=https://www.cambridge.org/core/journals/polar-record/article/question-of-icebergs-a-cryohistory-of-arctic-submarine-cables/451A8E2657363D298C58EA70D92F6FDB |journal=Polar Record |language=en |volume=58 |pages= |doi=10.1017/S0032247422000262 |bibcode=2022PoRec..58E..41A |issn=0032-2474}}</ref> [[Samuel Morse]] proclaimed his faith in it as early as 1840, and in 1842, he submerged a wire, insulated with tarred [[hemp]] and [[Natural rubber|India rubber]],<ref>{{cite web |title=[Heroes of the Telegraph&nbsp;– Chapter III.&nbsp;– Samuel Morse] |url=http://www.globusz.com/ebooks/Telegraph/00000013.htm |website=Globusz |access-date=2008-02-05 |url-status=dead |archive-date=2008-12-01 |archive-url=https://web.archive.org/web/20081201131615/http://www.globusz.com/ebooks/Telegraph/00000013.htm}}</ref><ref>{{cite web |url=http://inventors.about.com/library/inventors/bl_morse_timeline1.htm |archive-url=https://archive.today/20120709103139/http://inventors.about.com/library/inventors/bl_morse_timeline1.htm |url-status=dead |archive-date=July 9, 2012 |title=Timeline&nbsp;– Biography of Samuel Morse |publisher=Inventors.about.com |date=2009-10-30 |access-date=2010-04-25 }}</ref> in the water of [[New York Harbor]], and telegraphed through it. The following autumn, Wheatstone performed a similar experiment in [[Swansea Bay]]. A good [[insulator (electrical)|insulator]] to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. [[Natural rubber|India rubber]] had been tried by [[Moritz von Jacobi]], the [[Prussia]]n [[electrical engineering|electrical engineer]], as far back as the early 19th century.

Another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842. [[Gutta-percha]], the adhesive juice of the ''[[Palaquium gutta]]'' tree, was introduced to Europe by [[William Montgomerie]], a Scottish surgeon in the service of the [[East India Company|British East India Company]].<ref name=Haigh>{{cite book|last=Haigh |first=Kenneth Richardson |title= Cable Ships and Submarine Cables |year=1968 |publisher=[[Adlard Coles]] |location=London |isbn=9780229973637 }}</ref>{{rp|26–27}} Twenty years earlier, Montgomerie had seen whips made of gutta-percha in Singapore, and he believed that it would be useful in the fabrication of surgical apparatus. [[Michael Faraday]] and Wheatstone soon discovered the merits of gutta-percha as an insulator, and in 1845, the latter suggested that it should be employed to cover the wire which was proposed to be laid from [[Dover]] to [[Calais]].<ref name="guarnieri 7-1">{{Cite journal| last= Guarnieri|first=M.|year=2014|title=The Conquest of the Atlantic|journal=IEEE Industrial Electronics Magazine| volume=8| issue=1 |pages= 53–56/67|doi=10.1109/MIE.2014.2299492|s2cid=41662509}}</ref> In 1847 [[Carl Wilhelm Siemens|William Siemens]], then an officer in the army of Prussia, laid the first successful underwater cable using gutta percha insulation, across the [[Rhine]] between [[Deutz, Cologne|Deutz]] and [[Cologne]].<ref>{{cite journal |title=C William Siemens |journal=The Practical Magazine |date=1875 |volume=5 |issue=10 |page=219}}</ref> In 1849, [[Charles Vincent Walker]], electrician to the [[South Eastern Railway (UK)|South Eastern Railway]], submerged {{cvt|2|mi|0|disp=flip}} of wire coated with gutta-percha off the coast from [[Folkestone]], which was tested successfully.<ref name=Haigh/>{{rp|26–27}}

===First commercial cables===
[[File:British & Irish Magnetic Telegraph Co. Limited 3 shilling stamp c. 1862 remaindered without control number.jpg|thumbnail|right|A [[telegraph stamp]] of the British & Irish Magnetic Telegraph Co. Limited (c. 1862).]]

In August 1850, having earlier obtained a concession from the French government, [[John Watkins Brett]]'s [[English Channel Submarine Telegraph Company]] laid the first line across the [[English Channel]], using the converted [[tugboat]] ''Goliath''. It was simply a copper wire coated with [[gutta-percha]], without any other protection, and was not successful.<ref name=Haigh/>{{rp|192–193}}<ref>The company is referred to as the English Channel Submarine Telegraph Company</ref> However, the experiment served to secure renewal of the concession, and in September 1851, a protected core, or true, cable was laid by the reconstituted [[Submarine Telegraph Company]] from a government [[Hulk (ship type)|hulk]], ''Blazer'', which was towed across the Channel.<ref name=Haigh/>{{rp|192–193}}<ref name=Brett>{{cite journal|last=Brett|first=John Watkins|title=On the Submarine Telegraph|journal=Royal Institution of Great Britain: Proceedings: Vol. II, 1854–1858|date=March 18, 1857 |url=http://www.atlantic-cable.com/Article/Brett/index.htm|access-date=17 May 2013|type=transcript|url-status=dead|archive-url=https://web.archive.org/web/20130517155316/http://www.atlantic-cable.com/Article/Brett/index.htm |archive-date=17 May 2013}}</ref><ref name="guarnieri 7-1"/>

In 1853, more successful cables were laid, linking Great Britain with Ireland, [[Belgium]], and the [[Netherlands]], and crossing [[The Belts]] in Denmark.<ref name=Haigh/>{{rp|361}} The [[British & Irish Magnetic Telegraph Company]] completed the first successful Irish link on May 23 between [[Portpatrick]] and [[Donaghadee]] using the [[collier (ship)|collier]] ''William Hutt''.<ref name=Haigh/>{{rp|34–36}} The same ship was used for the link from Dover to [[Ostend]] in Belgium, by the Submarine Telegraph Company.<ref name=Haigh/>{{rp|192–193}} Meanwhile, the [[Electric & International Telegraph Company]] completed two cables across the [[North Sea]], from [[Orford Ness]] to [[Scheveningen]], the Netherlands. These cables were laid by ''Monarch'', a [[paddle steamer]] which later became the first vessel with permanent cable-laying equipment.<ref name=Haigh/>{{rp|195}}

In 1858, the steamship ''Elba'' was used to lay a telegraph cable from [[Jersey]] to [[Guernsey]], on to [[Alderney]] and then to [[Weymouth, Dorset|Weymouth]], the cable being completed successfully in September of that year. Problems soon developed with eleven breaks occurring by 1860 due to storms, tidal and sand movements, and wear on rocks. A report to the Institution of Civil Engineers in 1860 set out the problems to assist in future cable-laying operations.<ref>{{cite book |title= Minutes of Proceedings of the Institution of Civil Engineers |issue=Volume 20 |page=26}}</ref>

=== Crimean War (1853–1856) ===
In the [[Crimean War]] various forms of [[telegraphy]] played a major role; this was a first. At the start of the campaign there was a telegraph link at Bucharest connected to London. In the winter of 1854 the French extended the telegraph link to the [[Black Sea]] coast. In April 1855 the British laid an underwater cable from Varna to the [[Crimean peninsula]] so that news of the Crimean War could reach London in a handful of hours.<ref>{{cite book | author1=Christopher Andrew |title=The Secret World: A History of Intelligence |publisher=Penguin Books Limited |year=2018 |page=ccxiii |isbn=9780241305225 }}</ref>

===Transatlantic telegraph cable===
{{Main|Transatlantic telegraph cable}}
The first attempt at laying a transatlantic telegraph cable was promoted by [[Cyrus West Field]], who persuaded British industrialists to fund and lay one in 1858.<ref name="guarnieri 7-1"/> However, the technology of the day was not capable of supporting the project; it was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 with the world's largest steamship, the [[SS Great Eastern|SS ''Great Eastern'']], used a more advanced technology and produced the first successful transatlantic cable. ''Great Eastern'' later went on to lay the first cable reaching to India from Aden, Yemen, in 1870.

===British dominance of early cable===
[[File:Telegraph QE3 19.jpg|thumb|upright=1.15|Operators in the submarine telegraph cable room at the [[General Post Office|GPO]]'s Central Telegraph Office in London c. 1898]]

From the 1850s until 1911, British submarine cable systems dominated the most important market, the [[North Atlantic Ocean]]. The British had both supply side and demand side advantages. In terms of supply, Britain had entrepreneurs willing to put forth enormous amounts of capital necessary to build, lay and maintain these cables. In terms of demand, [[British Empire|Britain's vast colonial empire]] led to business for the cable companies from news agencies, trading and shipping companies, and the British government. Many of Britain's colonies had significant populations of European settlers, making news about them of interest to the general public in the home country.

British officials believed that depending on telegraph lines that passed through non-British territory posed a security risk, as lines could be cut and messages could be interrupted during wartime. They sought the creation of a worldwide network within the empire, which became known as the [[All Red Line]], and conversely prepared strategies to quickly interrupt enemy communications.<ref name="kennedy197110">{{cite journal | jstor= 563928 | title=Imperial Cable Communications and Strategy, 1870–1914 | url= https://archive.org/details/sim_english-historical-review_1971-10_86_341/page/728 | author=Kennedy, P. M. | journal= The English Historical Review |date=October 1971 | volume=86 | issue=341 | pages=728–752 | doi=10.1093/ehr/lxxxvi.cccxli.728}}</ref> Britain's very first action after declaring war on Germany in World War I was to have the [[CS Alert (1890)|cable ship ''Alert'']] (not the CS ''[[Telconia]]'' as frequently reported)<ref>Rhodri Jeffreys-Jones, ''In Spies We Trust: The Story of Western Intelligence'', page 43, Oxford University Press, 2013 {{ISBN|0199580979}}.</ref> cut the five cables linking Germany with France, Spain and the Azores, and through them, North America.<ref>Jonathan Reed Winkler, ''Nexus: Strategic Communications and American Security in World War I'', pages 5–6, 289, Harvard University Press, 2008 {{ISBN|0674033906}}.</ref> Thereafter, the only way Germany could communicate was by wireless, and that meant that [[Room 40]] could listen in.

The submarine cables were an economic benefit to trading companies, because owners of ships could communicate with captains when they reached their destination and give directions as to where to go next to pick up cargo based on reported pricing and supply information. The British government had obvious uses for the cables in maintaining administrative communications with governors throughout its empire, as well as in engaging other nations diplomatically and communicating with its military units in wartime. The geographic location of British territory was also an advantage as it included both Ireland on the east side of the Atlantic Ocean and Newfoundland in North America on the west side, making for the shortest route across the ocean, which reduced costs significantly.

A few facts put this dominance of the industry in perspective. In 1896, there were 30 cable-laying ships in the world, 24 of which were owned by British companies. In 1892, British companies owned and operated two-thirds of the world's cables and by 1923, their share was still 42.7 percent.<ref>Headrick, D.R., & Griset, P. (2001). "Submarine Telegraph Cables: Business and Politics, 1838–1939". ''The Business History Review'', 75(3), 543–578.</ref> During [[World War I]], Britain's telegraph communications were almost completely uninterrupted, while it was able to quickly cut Germany's cables worldwide.{{r|kennedy197110}}

===Cable to India, Singapore, East Asia and Australia===
[[File:1901 Eastern Telegraph cables.png|thumb|upright=1.15|Eastern Telegraph Company network in 1901. Dotted lines across the Pacific indicate planned cables laid in 1902–03.]]

Throughout the 1860s and 1870s, British cable expanded eastward, into the Mediterranean Sea and the Indian Ocean. An 1863 cable to Bombay (now [[Mumbai]]), India, provided a crucial link to [[Saudi Arabia]].<ref>{{cite news |url=http://www.telegraphindia.com/1080203/jsp/frontpage/story_8856997.jsp |title=The Telegraph&nbsp;– Calcutta (Kolkata) &#124; Frontpage &#124; Third cable cut, but India's safe |publisher=Telegraphindia.com |date=2008-02-03 |access-date=2010-04-25 |url-status=live |archive-url=https://web.archive.org/web/20100903041957/http://www.telegraphindia.com/1080203/jsp/frontpage/story_8856997.jsp |archive-date=2010-09-03 }}</ref> In 1870, Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872, these four companies were combined to form the mammoth globe-spanning [[Cable & Wireless plc|Eastern Telegraph Company]], owned by [[John Pender]]. A spin-off from Eastern Telegraph Company was a second sister company, the Eastern Extension, China and Australasia Telegraph Company, commonly known simply as "the Extension." In 1872, Australia was linked by cable to Bombay via Singapore and China and in 1876, the cable linked the British Empire from London to New Zealand.<ref>"Landing the New Zealand cable", pg 3, ''[[The Nelson Mail|The Colonist]]'', 19 February 1876</ref>

===Submarine cables across the Pacific, 1902–1991===
The first trans-Pacific cables providing telegraph service were completed in 1902 and 1903, linking the US mainland to Hawaii in 1902 and [[Guam]] to the [[Philippines]] in 1903.<ref>{{cite web|url=http://www.brainyhistory.com/events/1903/july_4_1903_69271.html |title=Pacific Cable (SF, Hawaii, Guam, Phil) opens, President TR sends message July 4 in History |publisher=Brainyhistory.com |date=1903-07-04 |access-date=2010-04-25}}</ref> Canada, Australia, New Zealand and Fiji were also linked in 1902 with the trans-Pacific segment of the [[All Red Line]].<ref>{{cite web |url= http://www.canadainternational.gc.ca/australia-australie/bilateral_relations_bilaterales/history-histoire.aspx?lang=eng |title= History of Canada-Australia Relations |publisher= Government of Canada |access-date= 2014-07-28 |url-status= dead |archive-url= https://web.archive.org/web/20140720185110/http://www.canadainternational.gc.ca/australia-australie/bilateral_relations_bilaterales/history-histoire.aspx?lang=eng |archive-date= 2014-07-20 }}</ref> Japan was connected into the system in 1906. Service beyond Midway Atoll was abandoned in 1941 due to World War II, but the remainder stayed in operation until 1951 when the FCC gave permission to cease operations.<ref>{{cite web |title=The Commercial Pacific Cable Company |url=http://atlantic-cable.com/CableCos/ComPacCable |publisher=Atlantic Cable |work= atlantic-cable.com |access-date=September 24, 2016 |url-status=live |archive-url = https://web.archive.org/web/20160927110415/http://atlantic-cable.com/CableCos/ComPacCable |archive-date=September 27, 2016 }}</ref>

The first trans-Pacific telephone cable was laid from Hawaii to Japan in 1964, with an extension from Guam to The Philippines.<ref>{{cite web |title=Milestones:TPC-1 Transpacific Cable System, 1964 |publisher=Engineering and Technology History WIKI |work=ethw.org |url=http://ethw.org/Milestones:TPC-1_Transpacific_Cable_System,_1964 |access-date=September 24, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160927020609/http://ethw.org/Milestones:TPC-1_Transpacific_Cable_System,_1964 |archive-date=September 27, 2016 }}</ref> Also in 1964, the [[Commonwealth Pacific Cable System]] (COMPAC), with 80 telephone channel capacity, opened for traffic from Sydney to Vancouver, and in 1967, the South East Asia Commonwealth (SEACOM) system, with 160 telephone channel capacity, opened for traffic. This system used microwave radio from Sydney to Cairns (Queensland), cable running from [[Cairns]] to [[Madang]] ([[Papua New Guinea]]), [[Guam]], Hong Kong, [[Kota Kinabalu]] (capital of [[Sabah]], Malaysia), Singapore, then overland by microwave radio to [[Kuala Lumpur]]. In 1991, the [[NPC (cable system)|North Pacific Cable system]] was the first regenerative system (i.e., with [[repeater]]s) to completely cross the Pacific from the US mainland to Japan. The US portion of NPC was manufactured in Portland, Oregon, from 1989 to 1991 at STC Submarine Systems, and later [[Alcatel Submarine Networks]]. The system was laid by Cable & Wireless Marine on the ''[[Cable Ship|CS]] Cable Venture''.{{citation needed|date=December 2024}}

===Construction, 19–20th century===
[[File:Bundesarchiv Bild 102-01035, New York, Verlegen von Unterseekabel.jpg|thumb|upright=1.15|right|Landing of an Italy-USA cable (4,704 nautical miles long), on [[Rockaway Beach, Queens]], New York, January 1925.]]
Transatlantic cables of the 19th century consisted of an outer layer of iron and later steel wire, wrapping India rubber, wrapping [[gutta-percha]], which surrounded a multi-stranded copper wire at the core. The portions closest to each shore landing had additional protective armour wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, with the exception of a rather high [[dielectric]] constant which made cable [[capacitance]] high. [[William Thomas Henley]] had developed a machine in 1837 for covering wires with silk or cotton thread that he developed into a wire wrapping capability for submarine cable with a factory in 1857 that became W.T. Henley's Telegraph Works Co., Ltd.<ref>{{cite web |title=Machine used for covering wires with silk and cotton, 1837 |publisher=The Science Museum Group |url=https://collection.sciencemuseumgroup.org.uk/objects/co44548 |access-date=24 January 2020}}</ref><ref name=Bright/> The [[India Rubber, Gutta Percha and Telegraph Works Company]], established by the Silver family and giving that [[Silvertown|name to a section of London]], furnished cores to Henley's as well as eventually making and laying finished cable.<ref name=Bright/> In 1870 [[William Hooper (chemist)|William Hooper]] established [[Hooper's Telegraph Works]] to manufacture his patented [[Vulcanization|vulcanized rubber]] core, at first to furnish other makers of finished cable, that began to compete with the gutta-percha cores. The company later expanded into complete cable manufacture and cable laying, including the building of the first cable ship specifically designed to lay transatlantic cables.<ref name=Bright>{{cite book |last=Bright |first=Charles |year=1898 |title=Submarine telegraphs: Their History, Construction, and Working |location=London |publisher=C. Lockwood and son |isbn= 9781108069489|lccn=08003683 |pages=125, 157–160, 337–339 |url=https://books.google.com/books?id=3DfeAgAAQBAJ&pg=PA157 |access-date=27 January 2020}}</ref><ref>{{cite web |last=Glover |first=Bill |title=History of the Atlantic Cable & Undersea Communications—CS Hooper/Silvertown |publisher=The Atlantic Cable |date=7 February 2019 |url=https://atlantic-cable.com/Cableships/Silvertown/index.htm |access-date=27 January 2020}}</ref><ref>{{cite web |last=Glover |first=Bill |title=History of the Atlantic Cable & Undersea Communications—British Submarine Cable Manufacturing Companies |publisher=The Atlantic Cable |date=22 December 2019 |url=https://atlantic-cable.com/CableCos/BritishMfrs/index.htm |access-date=27 January 2020}}</ref>

Gutta-percha and rubber were not replaced as a cable insulation until [[polyethylene]] was introduced in the 1930s. Even then, the material was only available to the military and the first submarine cable using it was not laid until 1945 during [[World War II]] across the [[English Channel]].<ref>Ash, Stewart, "The development of submarine cables", ch. 1 in, Burnett, Douglas R.; Beckman, Robert; Davenport, Tara M., ''Submarine Cables: The Handbook of Law and Policy'', Martinus Nijhoff Publishers, 2014 {{ISBN|9789004260320}}.</ref> In the 1920s, the American military experimented with rubber-insulated cables as an alternative to gutta-percha, since American interests controlled significant supplies of rubber but did not have easy access to gutta-percha manufacturers. The 1926 development by [[John T. Blake]] of deproteinized rubber improved the impermeability of cables to water.<ref>{{cite journal|last=Blake|first=J. T.|author2=Boggs, C. R.|title=The Absorption of Water by Rubber.|journal=Industrial & Engineering Chemistry |year=1926|volume=18|issue=3|pages=224–232|doi=10.1021/ie50195a002}}</ref>

Many early cables suffered from attack by sea life. The insulation could be eaten, for instance, by species of [[Teredo (bivalve)|''Teredo'']] (shipworm) and ''[[Xylophaga]]''. [[Hemp]] laid between the [[Steel wire armoured cable|steel wire armouring]] gave pests a route to eat their way in. Damaged armouring, which was not uncommon, also provided an entrance. Cases of sharks biting cables and attacks by [[sawfish]] have been recorded. In one case in 1873, a whale damaged the Persian Gulf Cable between [[Karachi]] and [[Gwadar]]. The whale was apparently attempting to use the cable to clean off [[barnacle]]s at a point where the cable descended over a steep drop. The unfortunate whale got its tail entangled in loops of cable and drowned. The cable repair ship ''Amber Witch'' was only able to winch up the cable with difficulty, weighed down as it was with the dead whale's body.<ref>[https://books.google.com/books?id=_hwAAAAAMAAJ&pg=PA311 "On Accidents to Submarine Cables"], ''Journal of the Society of Telegraph Engineers'', vol. 2, no. 5, pp. 311–313, 1873</ref>

===Bandwidth problems===
{{unreferenced section|date=December 2024}}
Early long-distance submarine telegraph cables exhibited formidable electrical problems. Unlike modern cables, the technology of the 19th century did not allow for in-line [[repeater]] [[amplifier]]s in the cable. Large [[voltage]]s were used to attempt to overcome the [[electrical resistance]] of their tremendous length but the cables' distributed [[capacitance]] and [[inductance]] combined to distort the telegraph pulses in the line, reducing the cable's [[Bandwidth (signal processing)|bandwidth]], severely limiting the [[Bit rate|data rate]] for telegraph operation to 10–12 [[words per minute]].

As early as 1816, [[Francis Ronalds]] had observed that electric signals were slowed in passing through an insulated wire or core laid underground, and outlined the cause to be induction, using the analogy of a long [[Leyden jar]].<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=Imperial College Press|year=2016|isbn=978-1-78326-917-4|location = London}}</ref><ref>{{Cite journal|last=Ronalds|first=B.F. |date=Feb 2016|title=The Bicentennial of Francis Ronalds's Electric Telegraph| journal=Physics Today|volume=69 |issue=2|pages=26–31 |doi= 10.1063/PT.3.3079|bibcode=2016PhT....69b..26R |doi-access=free}}</ref> The same effect was noticed by [[Latimer Clark]] (1853) on cores immersed in water, and particularly on the lengthy cable between England and The Hague. [[Michael Faraday]] showed that the effect was caused by capacitance between the wire and the [[ground (electricity)|earth]] (or water) surrounding it. Faraday had noticed that when a wire is charged from a battery (for example when pressing a telegraph key), the [[electric charge]] in the wire induces an opposite charge in the water as it travels along. In 1831, Faraday described this effect in what is now referred to as [[Faraday's law of induction]]. As the two charges attract each other, the exciting charge is retarded. The core acts as a [[capacitor]] distributed along the length of the cable which, coupled with the resistance and [[inductance]] of the cable, limits the speed at which a [[signal]] travels through the [[electrical conduction|conductor]] of the cable.

Early cable designs failed to analyse these effects correctly. Famously, [[E.O.W. Whitehouse]] had dismissed the problems and insisted that a transatlantic cable was feasible. When he subsequently became chief electrician of the [[Atlantic Telegraph Company]], he became involved in a public dispute with [[William Thomson, 1st Baron Kelvin|William Thomson]]. Whitehouse believed that, with enough voltage, any cable could be driven. Thomson believed that his [[law of squares]] showed that retardation could not be overcome by a higher voltage. His recommendation was a larger cable. Because of the excessive voltages recommended by Whitehouse, Cyrus West Field's first transatlantic cable never worked reliably, and eventually [[short circuit]]ed to the ocean when Whitehouse increased the voltage beyond the cable design limit.

Thomson designed a complex electric-field generator that minimized current by [[resonance|resonating]] the cable, and a sensitive light-beam [[mirror galvanometer]] for detecting the faint telegraph signals. Thomson became wealthy on the royalties of these, and several related inventions. Thomson was elevated to [[Lord Kelvin]] for his contributions in this area, chiefly an accurate [[mathematical model]] of the cable, which permitted design of the equipment for accurate telegraphy. The effects of [[atmospheric electricity]] and the [[geomagnetic field]] on submarine cables also motivated many of the [[International Geophysical Year|early polar expeditions]].

Thomson had produced a mathematical analysis of propagation of electrical signals into telegraph cables based on their capacitance and resistance, but since long submarine cables operated at slow rates, he did not include the effects of inductance. By the 1890s, [[Oliver Heaviside]] had produced the modern general form of the [[telegrapher's equations]], which included the effects of inductance and which were essential to extending the theory of [[transmission line]]s to the higher [[frequencies]] required for high-speed data and voice.

===Transatlantic telephony===
[[File:Submarine Telephone Cables PICT8182 1.JPG|thumb|right|<!--Five is dubious, I count only three – but then again I might be blind...-->Submarine communication cables crossing the Scottish shore at Scad Head on [[Hoy, Orkney|Hoy]], Orkney.]]

While laying a transatlantic telephone cable was seriously considered from the 1920s, the technology required for economically feasible telecommunications was not developed until the 1940s. A first attempt to lay a "[[pupinize]]d" telephone cable—one with loading coils added at regular intervals—failed in the early 1930s due to the [[Great Depression]].

[[TAT-1]] (Transatlantic No. 1) was the first [[transatlantic telephone cable]] system. Between 1955 and 1956, cable was laid between Gallanach Bay, near [[Oban]], Scotland and [[Clarenville, Newfoundland and Labrador]], in Canada. It was inaugurated on September 25, 1956, initially carrying 36 telephone channels.

In the 1960s, transoceanic cables were [[coaxial cable]]s that transmitted [[frequency-division multiplexing|frequency-multiplexed voiceband signals]]. A high-voltage direct current on the inner conductor powered repeaters (two-way amplifiers placed at intervals along the cable). The first-generation repeaters remain among the most reliable [[vacuum tube]] amplifiers ever designed.<ref>{{cite web |url =http://www.iscpc.org/information/Timeline_History.htm |title =Learn About Submarine Cables |publisher =International Submarine Cable Protection Committee |url-status =dead |archive-url =https://web.archive.org/web/20071213042957/http://www.iscpc.org/information/Timeline_History.htm |archive-date =2007-12-13 |access-date =2007-12-30 }}. From this page: In 1966, after ten years of service, the 1,608 tubes in the repeaters had not suffered a single failure. In fact, after more than 100 million tube-hours over all, AT&T undersea repeaters were without failure.</ref> Later ones were transistorized. Many of these cables are still usable, but have been abandoned because their capacity is too small to be commercially viable. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events.<ref>{{cite web |url= http://www.whoi.edu/science/GG/DSO/H2O/EOSarticle/H2O_article_revised_9.pdf |title=The Hawaii-2 Observatory (H2O) |author=Butler, R. |author2 =A. D. Chave |author3= F. K. Duennebier |author4=D. R. Yoerger |author5=R. Petitt |author6=D. Harris |author7=F.B. Wooding |author8 =A. D. Bowen |author9=J. Bailey |author10=J. Jolly |author11=E. Hobart |author12=J. A. Hildebrand |author13=A. H. Dodeman |url-status= live |archive-url= https://web.archive.org/web/20080226234700/http://www.whoi.edu/science/GG/DSO/H2O/EOSarticle/H2O_article_revised_9.pdf |archive-date=2008-02-26}}</ref>

===Other uses===
In 1942, [[Siemens Brothers]] of [[New Charlton]], London, in conjunction with the United Kingdom [[National Physical Laboratory, UK|National Physical Laboratory]], adapted submarine communications cable technology to create the world's first submarine oil pipeline in [[Operation Pluto]] during [[World War II]].

Active fiber-optic cables may be useful in detecting seismic events which alter cable polarization.<ref>{{cite journal |last1=Zhan |first1=Zhongwen |title=Optical polarization–based seismic and water wave sensing on transoceanic cables |journal=[[Science (journal)|Science]] |date=26 February 2021 |volume=371 |issue=6532 |pages=931–936 |doi=10.1126/science.abe6648 |pmid=33632843 |bibcode=2021Sci...371..931Z |s2cid=232050549 |url=https://www.science.org/doi/10.1126/science.abe6648}}</ref>