undersea cable

undersea cable, fiber-optic cable laid across the ocean floor that transmits information and enables worldwide communications. More than 600 cables with a combined distance of some 1,480,000 km (920,000 miles) stretch across the world.

Mechanics

Cables use fiber-optic technology to operate most efficiently. Lasers on one end of a cable line speedily transfer data along hairlike fiber-optic strands to receptors located on the other end of the cable. The cables are heavily protected and often wrapped in insulating materials such as rubber, steel, or tar. After being insulated, an undersea cable is about 2 to 3 cm (0.8 to 1.2 inches) thick. A common misconception is that satellites transmit most global data, but undersea cables are responsible for about 95 percent of international communications. Satellites are more expensive to manufacture and install in space and are more easily affected by solar flares and other environmental phenomena.

History

American inventor Samuel Morse was one of the first to propose laying a telegraph cable across the Atlantic Ocean in the early 1840s. Starting in 1857, the first of the Atlantic cable expeditions began when the British and the U.S. governments sent ships across the Atlantic to attempt to lay an undersea cable. One of the main financiers of such expeditions was American businessman and “father of the transatlantic cable” Cyrus Field, who himself crossed the Atlantic about 30 times in an effort to coordinate the cable’s success. The endpoints were Ireland and Newfoundland, then a British colony.

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telephone: Undersea cable

Initial attempts failed, during which cable faults led to multiple starts and stops, but in 1858 a cable successfully transmitted messages across the Atlantic Ocean. However, before it had been laid on the ocean floor, the cable was badly damaged by the elements. An unnecessarily high voltage was also run through the cable (an idea implemented by a British engineer), and transmission stopped after just three weeks. Less than 750 messages had been sent. In 1866 another cable was installed successfully, using knowledge gleaned from the short-lived 1858 cable. The cable allowed immigrants in the United States to communicate with their families across the ocean, and in 1881 the news of U.S. Pres. James Garfield’s assassination was immediately relayed to American allies overseas.

Cables continued to improve over time, and in 1956 a coaxial cable, which can transmit signals with low interference, was laid between the United Kingdom and North America. In 1988 the first fiber-optic undersea cable was laid between the United States, the United Kingdom, and France.

Damage and threats

On average, two to four undersea cables break every week, usually because of misplaced anchor drops or fishing equipment mishaps. Undersea events such as earthquakes can also cause breakage. However, such breaks rarely result in significant disruptions because service providers distribute their networks’ capacity over multiple cables in a method called network redundancy.

It is relatively uncommon for cables to be purposely sabotaged in warfare. However, the practice did occur during the Spanish-American War of 1898. The United States severed lines, many of which were British- or French-owned, to prevent Spain from staying in contact with its colonies in the Caribbean. The National Geographic Magazine, in 1901, described the Spanish-American War as “a story of ‘coal and cables.’ ” Britain used the same cable-cutting strategy during World War I to limit communications between Germany and the rest of the world. In retaliation, Germany attacked several Allied cable lines. The “cable wars” continued for the duration of the conflict.

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In February 2022 Russia invaded Ukraine, escalating the Russia-Ukraine War, which had begun in 2014. Starting in October 2023, cables that connected various countries in the Baltic region were unexpectedly damaged, disrupting communications between countries such as Finland and Estonia. The timing of the damage led to widespread suspicion that Russia had been tampering with communications between various Ukrainian allies. However, there is debate about whether the damage was purposeful, and one investigation’s results implied that the damage had been caused by an inexperienced crew.

Big tech’s cable race

Multiple technology companies announced undersea cable projects in 2024 and 2025. Such initiatives aim to increase these corporations’ control over customers’ bandwidth across the world and to ensure capacity for artificial intelligence (AI) initiatives.