Send a photo from Paris to a friend in New York and it lands before you’ve put your phone down. It feels as if it flew through the air, maybe bouncing off a satellite. It didn’t. For most of the trip, it raced along the floor of the Atlantic Ocean as flashes of light inside one of the world’s undersea internet cables.
These cables carry about 99% of the data that crosses the world’s oceans, yet for most of their length they’re only about as wide as a garden hose. TeleGeography, a firm that maps them, counts 607 cable systems in service and 102 more planned. Together they run for about 1.7 million kilometres, enough to wrap around the Earth more than 40 times.
So let’s follow that photo across the ocean, in (roughly) real time. The times below are rounded estimates for light racing through glass. In real life, your photo also makes a quick stop at the app’s own servers, but the ocean crossing works the same way.
0.000 seconds: You press send
Your photo leaves your phone as radio waves, but only as far as the nearest Wi-Fi router or mobile mast. From there, it becomes pulses of laser light inside glass fibres, each roughly as thin as a human hair.
Light in glass travels at about 200,000 kilometres per second, around two-thirds of its top speed in empty space. That’s fast enough to get from Paris to France’s Atlantic coast in a couple of thousandths of a second. Which is handy, because the coast is exactly where your photo is going.
0.003 seconds: A quiet building by the beach
In the seaside town of Saint-Hilaire-de-Riez, on France’s Atlantic coast, sits a cable landing station run by the telecoms company Orange. It’s where Google’s Dunant cable comes ashore. Dunant is one of 14 cable systems that cross the Atlantic today.
Landing stations rarely look like much. Often they’re plain buildings near a beach, with nothing to tell passers-by that a continent’s data flows through them. Close to shore, cables are wrapped in steel wire armour and buried up to 3 metres under the seabed. That keeps them out of reach of anchors and fishing gear.
0.005 seconds: Down to the deep
From here, Dunant runs about 6,600 kilometres to Virginia Beach in the US. Once it reaches deep water, it simply lies on the ocean floor, several kilometres below the waves. Out there, the cable is only about 25 mm (1 inch) across.
Inside, layers of plastic and steel wire protect the glass fibres at its heart, which can carry hundreds of terabits of data every second. Light fades over long distances, so repeaters along the route boost it. They run on electricity sent down the cable from the shore, at anywhere from 3,000 to 15,000 volts. Each cable is built to last at least 25 years down there.
Myth check: are sharks biting undersea internet cables?
In 2014, an old video of a shark chomping on a seabed cable went viral during the US’s annual Shark Week. Headlines warned that sharks were attacking the internet.
The truth is less dramatic. Sharks did bite some early fibre-optic cables off the Canary Islands in the mid-1980s. The culprit was the small crocodile shark, which swims as deep as 1,900 metres. Engineers toughened the cables’ outer layer and the problem went away.
The International Cable Protection Committee (ICPC) keeps records of cable faults. Fish bites caused less than 1% of them up to 2006, and none at all from 2007 to 2014. Verdict: the sharks are innocent. The real culprits are far more ordinary, as you’ll see below.
0.04 seconds: Your friend’s phone buzzes
About 0.035 seconds after you pressed send, your photo comes ashore in Virginia Beach. A few more thousandths of a second along fibre on land, and it’s in New York. Your friend sees it before you’ve even locked your screen.
For some people, even that is too slow. In 2015, Hibernia Networks opened Hibernia Express, a cable laid along the shortest possible route across the Atlantic. It cost about CAD 400 million. It cut the round trip between New York and London to under 59 milliseconds, more than 6 milliseconds faster than a rival link. Why bother? Financial traders will pay for every millisecond they can save.
And satellites? They’re great for remote places, but they carry only a sliver of international traffic. In the US, they make up just 0.37% of international capacity, according to TeleGeography.
What happens when a cable snaps?
Cables break more often than you’d think. The ICPC counts about 150 to 200 faults a year, roughly three or four every week. Around 70–80% are accidents caused by fishing gear and ships’ anchors. Deliberate damage, despite the headlines, makes up less than 1%.
Most of the time, you won’t notice. Internet companies spread traffic across several cables, so data takes another route while a specialist repair ship heads out. Its crew hooks the broken cable up from the seabed with a grapnel, splices in a new section and lowers it back down.
But when a country relies on a single cable, a break hurts. On 15 January 2022, an undersea volcano erupted near Tonga and shredded an 80-kilometre stretch of its only international internet cable. The repair ship had to come from Papua New Guinea, about 4,700 kilometres away. Tonga was almost cut off from the online world for over five weeks.
Big regions aren’t immune, either. In September 2025, several cables were damaged in the Red Sea, slowing the internet in India, Pakistan and the Gulf. Industry experts believe a ship dragging its anchor was to blame.
From a 16-hour telegram to a cable round the world
None of this is new. In 1858, the first telegraph cable across the Atlantic linked Ireland and Newfoundland. Queen Victoria sent a 98-word greeting to US President James Buchanan, and it took about 16 hours to get through.
That’s roughly six words an hour. At that pace, sending one second’s worth of Dunant’s data would take millions of years. The 1858 cable failed within weeks, after an engineer applied up to 2,000 volts trying to speed it up. A lasting link only arrived in 1866.
Today’s cables keep getting longer. In 2025, Meta announced Project Waterworth, a 50,000-kilometre cable system linking five continents. That’s longer than the distance around the Earth, and parts of it will lie up to 7,000 metres deep.
So, where is the internet?
Next time someone says your photos are “in the cloud”, you’ll know better. They’re stored in data centres. And to get between continents, they travel through undersea internet cables lying in the dark on the ocean floor, guarded from anchors, not sharks.
Did you know the internet ran under the sea? Tell us in the comments which fact surprised you most.
Speaking of the deep sea, find out whether AI can finally help us talk to animals, including the sperm whales clicking away down there. And if you can’t put your phone down long enough to think about any of this, check the 8 signs of phone addiction. Pin this one to remember what’s really under the waves.