The Submarine Cable System

The Submarine Cable System

This article relates to Twist

Much of Colum McCann's novel Twist takes place on a cable repair ship sent to locate and fix a breakage in the underwater cables conveying the globe's digital information pathways.

For many of us, perhaps because of the metaphorical terms used for internet storage and connection, such as cyberspace and the cloud, when we imagine the path of the world's information superhighway we look to the sky, perhaps envisioning some kind of literal cloud of information crackling above us, or at least high-powered satellite connections. However, on a bit-for-bit basis, even the most advanced satellite technology cannot begin to compete with the good old-fashioned Submarine Cable System, which is made up of hundreds of cables placed across the ocean floor, connecting continents and countries and delivering high-speed data transmissions, primarily internet traffic.

The History of the Submarine Cable System

The first submarine cables were laid for telegraphic transmission. This (now largely obsolete) communication system worked by sending electrical signals using Morse code to convey messages. The first successful transatlantic submarine cable was made from a simple copper wire, and it delivered about 12 telegraphed words per minute. On August 16, 1858, the first official telegram to pass between two continents was a letter of congratulations from the UK's Queen Victoria to the president of the United States, James Buchanan.

Over time, with advances in technology, undersea cables were upgraded and more widely distributed. In September 1956, the technology had advanced enough to link London and North America by telephone, with high-speed coaxial cables that used electrical radio frequency signals and could carry multiple voice channels. In 1988, the first transoceanic fiber-optic cable was installed, linking the US, the UK, and France. These cables revolutionized data transmission because of their volume, speed, and efficiency of data and voice communication. According to the US National Oceanic and Atmospheric Administration, "submarine cables are also an important means of power transmission—particularly in light of the ongoing development of offshore alternative energy generation facilities, such as wind farms."

Most submarine cables are about the width of a garden hose. They each contain bundles of fiber-optic filaments which are very thin, about the diameter of a human hair. There are currently 870,000 miles of fiber-optic lines running along the ocean floor.

How Do Submarine Cables Work?

Sending data through a cable uses the same principle as conducting electricity along a length of metal wire. Traditional cables used two differing electrical currents to transmit binary codes (a collection of 1s and 0s) to encode information. The device that receives the data interprets the code and converts it back into its original format. These days, almost all submarine cables along the ocean floor use fiber-optic technology. This means that instead of using electricity to create binary code signals, they send pulses of light to transmit the binary codes (think of a flashlight turning on and off: when the light is on, you are transmitting a 1; when the light is off, you are transmitting a 0). Because light travels faster than electricity, fiber-optic technology transmits information more rapidly than previous cables could.

Satellites Versus Submarine Cables

Undersea fiber-optic cables can carry far more data at a far lower cost than satellites. Satellites have traditionally been best for reaching regions not yet wired for fiber and distributing content to multiple locations. That said, the newest low earth orbit (LEO) satellites, which are currently being developed, rely on constellations of hundreds or thousands of small satellites orbiting at low altitudes to carry information at a faster rate than previous satellites could offer. As the demand for data roughly doubles every two years, these new options are seen as lucrative for companies and governments.

However, even with the newest advances, according to the NOAA site: "Over 95 percent of international data and voice transfers are currently routed through the many fiber optic cables that crisscross the world's seafloors." As of 2025, 570 active submarine cables are in service, and another 81 are being planned. In February 2025, Meta announced that they plan to construct the world's largest underwater cable network, which will connect the US, India, South Africa, Brazil, and other regions to help support its AI projects. This will involve a 31,000-mile subsea cable. Other companies are also developing projects, so there is no doubt that submarine cables will continue to be important means of transmitting information.

Submarine cable map, courtesy of Telegeography, CC BY-SA 4.0

Filed under Medicine, Science and Tech

This article relates to Twist. It first ran in the May 7, 2025 issue of BookBrowse Recommends.