There are many ways your Internet connection can malfunction. At the most mundane level, it could be a loose cable in your living room, a router crash, or an overloaded network. In the most sinister case, disruptions can occur far from home, deep beneath the sea, where the cables that support global Internet service are increasingly seen as vulnerable targets. But Finland is trying to do something using distributed acoustic sensing technology.
Underwater fiber optic cables currently carry approximately 99% of the world’s Internet traffic. The first transatlantic internet cable is being removed after about 40 years, having lain dormant on the seabed since 2002. Today, more than 550 cables lie deep beneath the waves, stretching a combined distance of about 870,000 miles around the world. Incidents resulting in damage to these undersea cables have increased since 2024 and ship anchors snapping internet cables are occurring more often than expected.
Although some of these scenarios are accidents, the recent rise raises concerns about possible state-sponsored sabotage. In some cases, the incidents took place in the Baltic Sea, which borders eight European countries and Russia, prompting Finland to take steps to protect its critical underwater infrastructure.
Listening to threats under the Baltic Sea
Since 2024, at least nine suspicious incidents involving ships pulling anchor have raised fears of sabotage of underwater internet cables. They took place in geopolitically sensitive areas such as the Baltic Sea and waters near Taiwan, raising concerns that these events could be linked to states seeking to disrupt communications and economic activity.
Finnish border guards have worked with the Finnish Navy and telecommunications company Elisa to deploy distributed acoustic sensing (DAS) technology in an effort to protect submarine cables in the Gulf of Finland. Cables suffered multiple cuts in late 2024, causing internet outages between Finland and Estonia, Finland and Germany, as well as Lithuania and Sweden. The DAS system uses a device that continuously sends short pulses of light through the optical fiber of a cable, causing it to act as a vibration sensor.
Underwater activity, such as an anchor dragging on the seabed, disrupts light pulses and can alert operators to a possible incident. The system has successfully completed field testing and will be used to alert Finnish authorities and cable operators of cable-related events so they can respond accordingly. Elisa’s Jouni Petrow described protecting underwater infrastructure as “an important task on a national scale”, with the aim of using technology to ideally inform authorities before damage occurs.
Alternative ways to protect submarine cables
As countries look to improve the security of their submarine fiber optic cables, additional solutions have emerged. Climate tech startup Indeximate, for example, has collaborated with a UK government-backed research organization to develop AI models, trained on ship tracking data, that can determine whether vibrations in DAS data come from ship activity like anchor dragging or natural ocean sounds that can be ignored. This AI system helps reduce false alarms and maintenance costs for cable operators because it does not require any additional hardware placed underwater.
Autonomous underwater vehicles (AUVs) can also be used to help protect underwater cables. Because DAS is a passive technology, it is unable to perform inspections or respond to suspicious activity. AUVs, meanwhile, can actively patrol underwater, scanning for changes in the seabed, examining cables closely, and monitoring for approaching threats. For example, New Zealand robotics company SYOS has developed an underwater AUV capable of monitoring cables alongside DAS. Satellites are also increasingly used to keep the internet up and running when damaged undersea cables interrupt connectivity.
SpaceX, for example, has been deploying thousands of small Starlink satellites into low-Earth orbit since 2019. Space networks can provide a backup if hardlines are cut, maintaining internet service for remote areas and critical sites until damaged cables are repaired. When Tonga’s undersea cable was severed by a volcanic eruption in 2022, SpaceX donated Starlink terminals that allowed the country to stay online for five weeks while repairs were made.
