On this day 186 years ago, Samuel Morse received US Patent No. 1647A for his “American Electro-Magnetic Telegraph”. Morse’s groundbreaking invention paved the way for rapid long-distance communication across the oceans.Today, modern fibre-optic cables handle more than 95% of all international data traffic. Though the history of how the ocean floor was wired is vast and storied, the British Empire’s use of this emerging technology in the late 19th and early 20th centuries to further its expansionist ambitions marked a defining chapter.This is how Britain built the world’s first communications empire, turning undersea cables into invisible instruments of imperial control and geopolitical leverage.Communications and the ‘All-red Line’In the early 19th century, the British Empire found it nearly impossible to implement a unified governance model across the vast expanse of its colonial holdings.The speed of information was bound to a ship traversing the vast oceans. Historian Daqing Yang said in a 2009 paper: “Geographical limits of empires were determined by the possibility for effective communication.” Though the telegraph began to shrink this vastness, it was initially confined only to overland communications.The year 1851 saw a giant leap. The Submarine Telegraph Company, a British firm, laid the world’s first ever successful undersea cable, across the English Channel. A French fisherman, however, severed it shortly after its first transmission.Story continues below this adIt was not until 1866 that a lasting transatlantic cable was laid down across the ocean by American businessman Cyrus W Field, the founder of the Atlantic Telegraph Company. Quick to identify the advantages of rapid communications, the British initiated an aggressive campaign to wire the globe, handing over the task of building and developing these wires to domestic companies.This resulted in the eventual formation of the “All-Red Line” — the nervous system of the British Empire, named so owing to the red ink used to indicate colonial territory on maps at the time. World cable map from 1901. Source: William Clauson-Thue, The ABC Universal Commercial Electric Telegraphic Code, 5th ed. (London: Eden Fisher and Co., 1901)By 1892, the British controlled 66% of the world’s cable networks spanning almost 164,000 km, according to a 2025 paper, Undersea cables and the extension of Empire.Story continues below this adSoon enough, other powers such as the US, Japan and the Dutch also began laying their own undersea cables, says the paper, authored by Motohiro Tsuchiya (Graduate School of Media and Governance) and Kristi Govella (Oxford School of Global and Area Studies).By 1908, the British share of undersea networks was at 56.2% (2,65,971 km). The country with the second largest share in that year was the US, with a 92,434 km network, according to the paper.The network was often routed through British-controlled territories and cable stations rather than along the shortest geographical paths, reducing dependence on foreign powers and enhancing the security of imperial communications.Cables were drawn from the Strait of Gibraltar into the Mediterranean, routed through Malta and the Suez Canal, into the Red Sea, across the Indian Ocean to Bombay, and stretched as far as Hong Kong, says the paper.Story continues below this adLondon effectively monopolized global information flows forcing rival nations to navigate a communications system strictly governed by the British Crown.Communications and tactical dominanceThe All-Red Line empowered the British in multiple ways. Information flowed in and out of London at an unprecedented rate. Financial institutions heavily leveraged this system to instantly exchange information on weather patterns, shipping routes and fluctuating prices of cargo at various ports, according to Undersea cables and the extension of Empire. A map of undersea internet cables today. TeleGeographyMilitarily, the system allowed the rapid deployment of the British forces. Story continues below this adIt was not until 1914, however, that the true tactical value of this infrastructure was displayed. One of the very first acts by the British after the eruption of World War I was to deploy a cable ship to dredge up and sever Germany’s transatlantic telegraphic cables. Though Germany responded similarly, the strength and size of the British telegraph network was maintained during both World Wars.Undersea cables in modern timesToday, the geopolitical logic of the All Red-Line has carried forth. Undersea cables remain the vital yet invisible backbone of critical infrastructure like the Internet.Modern geopolitical tensions are evident in the competition between the US and China, with both powers closely scrutinising and competing over undersea cable projects in the Indo-Pacific. More than a century after they first emerged as tools of empire, these networks continue to shape regional alignments and strategic partnerships.Story continues below this adA key differentiator between the 19th-20th century networks and today is the arrival of private tech monoliths. US-based hyperscalers like Meta and Amazon have emerged as chief players in the construction, leasing and operation of most submarine cables. States continue to co-operate with such companies to ensure national strategic interests are protected.