The recent major disruption of key Internet services is being attributed to the damage (possibly by Houthi rebels) to three submarine communication cables in the Red Sea off the coast of Yemen. What exactly are these submarine communication cables, why are they needed, and what do such communication cables look like today?

Why underwater communication cables are important

Even today, when we mostly use mobile devices, have a network of communication satellites and access to the “space Internet,” the lion’s share of Internet traffic, 99% in fact, goes through good old-fashioned cables. Yes, now it’s fiber optics, not archaic copper wires, but mobile traffic ends at the provider’s servers, and then it still goes through cables to the backbone communication networks, the so-called Internet backbone, which connects the main points of exchange of Internet traffic in countries and continents.

It is the stability of the main segments of the Internet backbone that determines the stability of the entire network. Due to the very architecture of the Internet, the absence of a central structure, redundancy of network connections and the possibility of switching, the stability of the global network is extremely high, but… in case of damage to any main information highways, the load on other segments increases, delays increase, which can eventually lead to global disruptions, such as the one that occurred on March 5, 2024.

On land, the main segments of the Internet are mostly underground cable networks, but when it comes to connections between continents, undersea communication cables are indispensable. Just like trade routes, undersea Internet cables have circled the globe and mostly follow the same paths as ships. What can you do, information is modern oil.

Submarine communication cables are also being laid in places where building a terrestrial network is difficult. For example, all the cities on the Brazilian coast are connected by the Brazilian Festoon submarine cable, which was laid in 1996; small towns on the Pacific coast of Canada will be connected by the Connected Coast submarine cable this year; most cities in Alaska will be connected by the AU-Aleutian (2022), Airraq (2024), and Nome to Homer Express (2027) cables.

But the foundation of the foundation is, of course, transoceanic cables: Europe – America across the Atlantic, America – Asia across the Pacific, and Asia – Europe along the East Asian coast, through the Bay of Bengal, the Arabian Sea, the Red Sea (yes, this is where the cables were cut) to the Mediterranean.

How it all started

The need to connect the continents, primarily Europe and the United States, with reliable and fast communication became clear almost immediately after the introduction of the first commercial electric telegraph by Cook and Wheatstone in 1838.

Already in 1840, Samuel Morse declared the necessity and possibility of laying a telegraph cable across the Atlantic. Moreover, he proved his idea in practice by immersing a cable insulated with tarred hemp and rubber into the waters of New York Bay in 1842 and telegraphing along it. Later, this experiment was repeated by Charles Wheatstone in England. In addition to rubber, the first cables were insulated with gutta-percha, a natural polymer extracted from the tree of the same name that grows in India and the islands of Southeast Asia. It was gutta-percha that became the basis of the insulation for the first transatlantic cable and many other cables.

The first submarine cable was laid in 1847 by Karl Wilhelm Siemens, the brother of Werner von Siemens, the founder of Siemens. The cable, insulated with gutta-percha, ran across the Rhine River and connected the cities of Cologne and Deutsch (now a district of Cologne).

The first commercial maritime telegraph cable was laid, of course, across the English Channel. In 1850, the English Channel Submarine Telegraph Company threw an unprotected gutta-percha-insulated cable across the strait, but it soon failed, either because of rubbing against rocks from the waves or because of damage from a fishing boat anchor. In 1851, the reformed Submarine Telegraph Company laid a new four-core cable (they were immediately banking on increased traffic!), now protected by a spiral metal braid. The 46-kilometer-long cable was made by the Gutta Percha Company (founded in 1845), and the protective braid was made by Wilkins and Wetherly, a company that specialized in the manufacture of ropes and tackle for sailboats. This division of labor between cable and braid manufacturers existed for a long time.

In the early history of submarine cables, there is a place for… Crimea. During the Crimean War (1853-1856), when the Allied forces were giving Tsarist Russia a good thrashing, a telegraph line was laid from London to Bucharest to control the troops. In 1854 it was extended to Varna, and in 1855 it was brought to Balaklava in the Crimea, where British troops were stationed, along the bottom of the Black Sea. Messages and news from the Crimea reached London in less than an hour. It was the first war to use the telegraph, almost an “online war” at the time.

After all this, it became clear that submarine cables worked, and the idea of laying a cable across the Atlantic in 1854 was seized upon by American businessman Cyrus W. Field and English inventor Frederick Newton Gisborne. The Atlantic Telegraph Company was established, 4,600 kilometers of cable were ordered (by the Gutta Percha Company plus several rope manufacturers, as the volume was unheard of at the time), and modern steam-powered warships were leased from the US and British governments to lay the cable.

The first transatlantic cable had 7 copper wires, three layers of gutta-percha insulation, a tallowed hemp winding, and a spiral protection made of metal wires. The weight of the cable was 550 kg/km, it was relatively flexible and had to withstand a load of several tens of kilonewtons. But the first few attempts at laying the cable were still unsuccessful. The cable broke, got lost at sea, ships were hampered by storms, and so on. However, on the third attempt, on August 5, 1858, the cable was completed. The first test message was sent from Newfoundland to Ireland on August 10, 1858.

In fact, this first oceanic cable transmitted only 732 messages before failing in September of that same year, 1858. This was due to insulation damage after an attempt to apply too much voltage and to the poor design of the cable itself. In addition, the first cables did not have signal repeaters, so due to fading, the transmission speed was terrible – 2 minutes for just one letter!

But there was no stopping the entrepreneurs. A new attempt to lay a cable across the ocean took place in 1865, and another in 1866. At that time, there were already submarine cables in the Mediterranean and Red (!!!) Seas, technology had improved significantly, and a kilometer of cable weighed only 70-100 kg instead of 550 kg. The largest ship in the world at that time, the SS Great Eastern, took part in the laying of the cable. On July 13, 1866, a new cable was laid, and on September 7, 1866, another one was laid, thanks to the found end of the wire lost in the previous attempt. These new cables were super-fast – using Morse code and new equipment, up to 8 words per minute could be transmitted!

Additional cables were laid across the Atlantic in 1873, 1874, 1880, and 1894. By the end of the nineteenth century, every major country, Great Britain, France, Germany, and the United States, had its own transatlantic cable.

In 1871, all of the Earth’s continents, except Antarctica, were connected by submarine telegraph cables. The cable across the Pacific Ocean, the United States – Hawaii – Guam – Philippines, was laid in 1903.

Telephone conversations began to be transmitted through submarine cables across the Atlantic only in 1956, when a special coaxial telephone cable TAT-1 was laid. It supported 35 telephone conversations at once, with another channel reserved for 22 telegraph lines. In the 1960s, the first signal amplifiers appeared, of course, tube amplifiers.

And now what? Fiber optics!

In the 1970s, optical fiber was created. The first fiber optic telephone cable, TAT-8, was laid under the Atlantic in 1986. It operated until 2002, providing traffic transmission speeds, now digital, of up to 280 Mbps.

The commissioning of this particular cable convinced IBM to fund the creation of a dedicated channel between Cornell University and CERN. This provided Tim Berners-Lee with high-speed and direct access to the National Science Foundation Network, which in turn helped in the demonstration of the World Wide Web, which took place only 10 months later. The Internet as we know it today was born. Since then, all submarine and land-based information highways have been made of fiber optics.

Of course, a modern submarine communication cable is very different from the one that was laid under the English Channel in 1851. It now has fiber optics in the center, but in general, it is also a multilayer structure with several levels of protection. And, interestingly, because of the better protection, it is even heavier than the nineteenth-century cable.

Modern submarine communication cables have a diameter of 25 to 69 mm and weigh from 1 to 1.5 tons per kilometer. Thinner cables are used in deep water; thicker ones are laid near the shore to protect them from accidental damage by ship anchors, landslides, and animals. As it turned out, sharks like to attack cables.

In cross-section, a modern submarine communication cable consists of the following layers (from edge to center):
1. Polyethylene
2. Mylar (lavsan)
3. Twisted steel wire
4. Aluminum waterproofing partition
5. Polycarbonate
6. Copper or aluminum pipe
7. Petrolatum (petroleum jelly)
8. Optical fibers

Despite their fairly robust structure, the cables are regularly damaged by fishing trawlers, anchors, earthquakes, muddy streams, etc. But, unlike in the 19th century, modern equipment allows cables to be repaired. In the Atlantic alone, about 50 such repairs are carried out annually.

Special cable ships are used to lay and repair submarine cables, which are in the fleets of almost all major countries and are owned by large companies involved in this business.

Red Sea and other important areas

According to the Submarine Cable Map website, by the end of 2023, 529 submarine cable systems with 1,444 connection points to the network on land are operating and under construction worldwide.

There are submarine communication cables even in our Black Sea, which seems to be an inland sea and which is seemingly easy to bypass from any side. These are the Georgia-Russia line (Poti – Sochi – Novorossiysk), built in 2000, the cables across the Kerch Strait that the occupiers laid in 2014 and 2017, the KAFOS cable that connected Turkey to Bulgaria and Romania in 1997, and the Caucasus Cable System (2008), which runs across the sea from Georgia to Bulgaria.

According to the Submarine Cable Map, the major hubs where many submarine cables converge are: Marseille, Suez Canal, Singapore, Hong Kong, Tokyo. These are the areas with the highest number of cables: Mediterranean Sea, Red Sea, Arabian Sea, East and South China Seas, and the Caribbean.

The cable bundle passes through the relatively narrow (26.5 km) and shallow (average depth – 186 m) Bab el-Mandeb Strait. There are 12 cables lying on the bottom, including the damaged Asia-Africa-Europe 1 (AAE-1), Europe India Gateway, and Seacom-TGN-Gulf cables. Another 5 cables across the Red Sea are under construction and are due to be commissioned in 2024-25.

Submarine Cable Map presents a very visual map of submarine communication cables that is regularly updated. You can search for cables here by year of commissioning, country, landfall point, etc. I advise you to look at 2024-2027: the construction of submarine cables is going at a frantic pace, because the volume of Internet traffic is also growing every year.

Cases of attacks on underwater cables

As we have already noted, submarine communication cables are subject to a variety of natural and uncontrollable causes. But sometimes people also damage cables.

The first recorded intentional damage to a submarine cable network occurred during World War I. On September 7, 1914, the Germans sent the light cruiser Nurnberg to raid Fanning Atoll in the Central Pacific. There was a relay station of the All Red Line cable system that connected all the continents. The repeaters and power supply were destroyed, cables and tools were damaged. The connection was restored only in two weeks.

For the next 100 years, people didn’t touch the cables, until in March 2007, when pirates stole an 11-kilometer section of the T-V-H submarine cable connecting Thailand, Vietnam, and Hong Kong. The attackers tried to sell 100 tons of cable for scrap.

From January 23 to February 4, 2008, there was a series of 6 consecutive damages to submarine cables in the Persian Gulf, the Mediterranean Sea and the Indian Ocean. Although it was officially reported that the causes of the accidents were common (ship anchors, etc.), conspiracy theorists believe that the US intelligence services were behind the damage, trying to prevent Iran from trading oil in this way. Or that it was an unsuccessful attempt to install spyware on the cable.

Speaking of spies and submarine cables. In 1971, the United States, using a modified USS Halibut submarine, installed a contactless device for reading and recording telephone conversations over a secret submarine cable in the Sea of Okhotsk that connected the USSR Navy base in Petropavlovsk-Kamchatsky to the Pacific Fleet headquarters in Vladivostok. And then they would visit the device every month to collect the tapes and install new ones. The information about the Ivy Bells operation was leaked by a retired US NSA employee who lost a large sum of money and went to the KGB to sell all the secrets he knew for only $40,000.

It is not yet clear who is responsible for the damage to the submarine cables. The German traffic exchange operator DE-CIX (Deutsche Commercial Internet Exchange) believes that the cables were damaged after a cargo ship that was attacked in the Red Sea in February 2024 drifted uncontrollably with its anchor down. This apparently refers to the bulk carrier Rubymar, carrying a cargo of toxic fertilizers, which was fired upon by anti-ship missiles and attacked by underwater drones on February 18, 2024. The crew abandoned the ship, which drifted for 11 days before sinking on March 2, 2024.

On the other hand, in early February 2024, the Yemeni government warned that the Houthis were planning an attack on submarine cables. So this is also possible.

It is also unclear how the damaged submarine cables will be repaired. Due to the Houthis’ shelling of the ships, the last of which took place on March 4, 2024, it is at least dangerous. Terrorists use fairly modern ballistic and cruise anti-ship missiles of Soviet-Russian, Iranian and Chinese production (I wonder who provided them with them…), and a repair ship is a huge stationary target. So it is possible that global problems with the Internet are just beginning.