Attacks on undersea cables: a Victorian legacy

By: James Fargher

ETC Cables
The Eastern Telegraph Company’s undersea network, 1901. Source Wikimedia

In October 2015 The New York Times reported on heightened US concerns about Russian submarines near undersea internet cables.[1] Citing unnamed intelligence officials and diplomats, the article highlighted growing fears that Russian submarines could sever the cables which pipe 95% of the internet around the world.[2] The piece prompted a flurry of interest in this possible new threat to global electronic traffic,[3] [4] but attacks on undersea communications cables have actually been a common tactic used in naval warfare since the 19th century. Beginning with the invention of the telegraph, networks of undersea wires have been used by the global powers as nervous systems to link together far-flung military forces, territories, and business interests. Naval attacks on these undersea cables have proven to be a successful tactic in previous conflicts.

Invented by Samuel Morse in 1837, the electrical telegraph was the Victorian equivalent of the Internet. Developed during a time when the maximum speed of information flow was as fast as a galloping horse or the speed of a sailing ship, the telegraph revolutionised the world with the ability to communicate more-or-less instantly. By the 1840s webs of telegraph wires had been laid across Europe and North America,[5] but they were vulnerable to being tapped or severed by armies during wartime. The only real way of preventing attacks on the wires was to lay them as cables along the bottom of the sea, coated with gutta-percha, a tough plastic substance produced from Malaysian trees, to insulate the copper wires from saltwater. [6]

Undersea cables could be intercepted by enemy ships, however, as was demonstrated in 1850 when hours after the first cable was laid across the English Channel, it was inadvertently snapped by an unsuspecting fisherman.[7] Armouring the cables with iron or steel could protect them from sea creatures, but ships’ crews could still haul up the lines and saw through them, potentially cutting off whole territories from the world telegraph network. This threat became increasingly serious throughout the 19th century, with the growing realisation that the Powers were becoming dependent on telegraph wires to project global power.[8] Britain in particular relied on a network of undersea cables to connect London with its sprawling Empire and to coordinate the fleet which was deployed in a series of naval stations around the world.[9] So seriously did the British take the security of the cable network, that Whitehall developed a near-obsession with developing an ‘all-red’ routes of telegraph wires which only touched the seabed or British territory so that they could not be interrupted by the enemy in wartime.[10]

Although the cables remained relatively safe in deep water, such as the mid-Atlantic, they were vulnerable in shallow waters, such as the English Channel, the Mediterranean, and the North Sea where they could be dredged with grappling hooks.[11] The imperial Russian Black Sea fleet, for example, drew up plans to sever the cable running between Gibraltar and Alexandria during an international crisis with Britain over Afghanistan in 1885, which would have severed all electronic communication with India, South Africa, Singapore, and Australasia.[12] Cables were also exposed whenever they surfaced, either at their destinations, such as Porthcurno in Cornwall, or at the electronic booster stations needed to repeat the signals over long distances. These booster stations were often located in the naval bases that Britain established around the world, such as Aden, Simon’s Bay, and Gibraltar, but sometimes were located on undefended islands such as the Falklands.[13] Indeed, following the recommendations first made by the Carnarvon Commission in 1879, huge amounts of money were spent in fortifying the most important stations (Aden in particular), to defend the dockyards and communications nodes.[14]

One of the first instances in which undersea cables were actually attacked came during the 1879-1883 War of the Pacific between Chile and Bolivia and Peru. Chilean naval forces severed the main cable which connected Lima to San Francisco, effectively cutting off Peru from much of the world’s telecommunications and disrupting American and British media coverage of the war.[15] More worryingly for the British, during the 1898 Spanish-American War, the US Navy cut through several British-owned cables connecting Cuba with the international network, despite the fact that Britain remained neutral during the conflict and despite protests from London.[16]

The most well-known case of cable cutting, however, came in 1914, hours after Britain declared war on Germany.  Shortly after the midnight expiration of Britain’s ultimatum to Germany, CS Alert steamed out of Dover and out into the North Sea on 5 August. By morning, she had fished up and severed the five undersea telegraph cables connecting Germany with the outside world.[17] Cut off from her colonies and from neutrals outside of Europe, Germany was forced to rely instead on wireless transmissions to communicate with her naval and colonial forces stationed abroad, as well as with her diplomatic missions overseas. These transmissions were intercepted and decoded by the Admiralty in London,[18] which also dispatched cruisers to systematically knock out the German transmitter stations in Africa and the Pacific and the German squadrons attempting to attack British booster stations.[19] But the most significant achievement came in 1917, when the Admiralty intercepted the famous Zimmerman telegram sent wirelessly from Berlin to the German ambassador in Mexico, with instructions to persuade the Mexican government to declare war on the United States. The decoded message was presented to the Americans, and the Zimmerman telegram became one of key factors which pushed the US Congress to declare war on Germany in April 1917.

Cables were also regularly cut in the Second World War, although the submarine added a new dimension to cable warfare. As early as 1924, the Admiralty warned the government that submarines were capable of severing even the wires laid along the seabed.[20] Although Allied cables remained relatively safe from attack in the Atlantic during the war, British cables and repeater stations came under attack from the Imperial Japanese Navy in the Indian and Pacific oceans. The British, in turn, developed midget submarines capable of severing communications cables. XE4, for example, successfully cut the cable connecting Saigon with Hong Kong in July 1945.[21]

Since the Second World War, there have been no deliberate instances of navies cutting undersea communication cables, although cables have been tapped by submarines.[22] As attacks in the past have demonstrated, it is relatively easy for small craft to locate and destroy the undersea wires. Even today cables are routinely broken by natural forces and by accident, including an incident in February 2012 when a civilian ship dropped anchor in a restricted zone off Mombasa harbour, slicing through the fibre optic cable providing internet service to all of East Africa.[23] Although undersea cables have not been attacked since 1945, given the modern world’s reliance on undersea wires to carry electronic traffic around the world they could prove to be important strategic targets in future conflicts.



James A. Fargher is a doctoral candidate in the Laughton Naval History Unit in the Department of War Studies, specialising in British naval and Imperial history. See his previous article for Strife on the Origins of British Counterinsurgency Strikes.





[1] David Sanger and Eric Schmitt, ‘Russian Ships Near Data Cables Are Too Close for U.S. Comfort,’ The New York Times, 25 October 2015. Web.

[2] Anthony Cuthbertson, ‘US fears Russian submarines cutting undersea internet cables,’ International Business Times, 26 October 2015. Web.

[3] Peter Cooney, ‘U.S. Concerned by Russian operations near undersea cables: NY Times,’ Reuters, 25 October 2015. Web.

[4] ‘Fears over Russian submarine and spy ship patrols near vital undersea internet cables,’ Daily Mail, 26 October 2015. Web.

[5] Daniel R. Headrick and Pascal Griset, ‘Submarine Telegraph Cables: Business and Politics, 1838-1939,’ The Business History Review 75: 3 (2001), 545.

[6] Paul Kennedy, ‘Imperial Cable Communications and Strategy, 1870-1914,’ The English Historical Review, 86: 341 (1971), 728.

[7] Headrick and Griset, ‘Submarine Telegraph Cables: Business and Politics, 1838-1939,’ 546.

[8] National Archives, Kew, FO 78/1785, Foreign Office Records: Turkey, Turkish & Red Sea Lighthouses, 1859-1863,’ P&O Company Secretary to Lord John Russell, letter, 8 September 1859.

[9] Daniel Headrick, The Tentacles of Progress: Technology Transfer in the Age of Imperialism, 1850-1940 (Oxford: Oxford University Press, 1988), 108.

[10] Archibald Spicer Hurd, ‘An All-British Cable System: Cables as Auxiliary Weapons of Imperial Defence,’ 1899 Foreign and Commonwealth Office Collection,

[11] Kennedy, ‘Imperial Cable Communications and Strategy, 1870-1914,’ 732.

[12] Ibid.

[13] Archibald Spicer Hurd, ‘An All-British Cable System: Cables as Auxiliary Weapons of Imperial Defence,’ 1899 Foreign and Commonwealth Office Collection,

[14] British Library, London, IOR/MSS Eur/D604/62, India Office Records, Letter from the Undersecretary of State for India to the Secretary of State for War, February 1884.

[15] John A. Britton, Cables, Crises, and the Press: The Geopolitics of the New Information System in the Americas, 1866-1903 (University of New Mexico Press, 2013), 72.

[16] Headrick and Griset, ‘Submarine Telegraph Cables: Business and Politics, 1838-1939,’ 565.

[17] Jonathan Reed Winkler, Nexus: Strategic Communications and American Security in World War I (Boston: Harvard University Press, 2009), 5.

[18] William Storey, The First World War: A Concise Global History (London: Rowman & Littlefield, 2014), 108.

[19] Phillip Pattee, ‘British Naval Strategy in the First Months of the Great War,’ Lecture, 1914: Global War & American Neutrality, National World War I Museum, Kansas City. Web.

[20] Daniel Headrick, The Invisible Weapon: Telecommunications and International Politics, 1851-1945 (Oxford: Oxford University Press, 1991), 245.

[21] Paul Akermann, Encyclopedia of British Submarines 1901-1955, (Penzance: Periscope Publishing, 2002), 459.

[22] Olga Khazan, ‘The Creepy, Long-Standing Practice of Undersea Cable Tapping,’ The Atlantic, 16 July 2013. Web.

[23] ‘Ship’s anchor slows down East African web connection,’ BBC News, 28 February 2012. Web.

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