Almost everything that crosses an ocean digitally, bank settlements, video calls, cloud backups, the traffic behind an ordinary Google search, travels through a strand of glass on the seabed. Roughly 500 active submarine cables, totalling more than 1.4 million kilometres, carry the overwhelming majority of intercontinental data. Satellites, for all the attention they attract, move only a small fraction, because a single modern cable can carry hundreds of terabits per second at latencies no orbit can match.
The physical object is unglamorous. In deep water a cable is about the width of a garden hose: a few pairs of optical fibre, a copper conductor, steel strength members and polyethylene sheathing. Closer to shore, where trawlers and anchors operate, it gains layers of galvanised steel armour and is buried a metre or more into the seabed by a sea plough towed behind the laying ship. Every 60 to 80 kilometres a repeater boosts the optical signal, powered by up to 10,000 volts of direct current fed down the copper from the landing stations at each end. Those landing stations cluster in predictable places, and Britain is unusually dense with them: Cornwall alone, around Bude and Widemouth Bay, terminates a large share of transatlantic capacity, including Google's Grace Hopper cable, which came ashore there in 2022.
Ownership has shifted in the past decade. Where consortia of national telecoms firms once dominated, Google, Meta, Microsoft and Amazon now fund or wholly own a substantial share of new builds, because their data centres generate the demand. The construction industry itself remains tiny: a handful of firms, among them Alcatel Submarine Networks, SubCom and NEC, manufacture and lay nearly all of it.
Faults are not rare events. The International Cable Protection Committee, the industry body that coordinates protection standards, records roughly 150 to 200 cable faults worldwide each year. The dull majority, somewhere around three quarters, come from fishing gear and ship anchors dragged across shallow routes. The famous shark bites were real, Bell engineers documented attacks on early fibre systems in the 1980s, apparently drawn by electromagnetic fields, but modern armouring has reduced them to a footnote. Earthquakes and submarine landslides do the occasional spectacular damage: a 2006 quake off Taiwan severed multiple cables at once and disrupted traffic across East Asia for weeks.
The repair bottleneck
What turns a routine fault into a strategic problem is the repair system. There are only a few dozen cable ships in the world, and fewer still held on standby under regional maintenance agreements, such as the Atlantic Cable Maintenance Agreement that covers UK waters. When a cable fails, operators locate the break by measuring how far light travels down the fibre before reflecting back, then dispatch a ship that may be days away. The crew drags a grapnel across the seabed to hook the cable, hauls each severed end to the surface, splices in a new section on deck under microscopes, tests it, and lowers the joint back down. A straightforward repair takes one to two weeks; bad weather, deep water or a queue of prior jobs can stretch it to months. The fleet is ageing, and shipyards are not replacing it quickly.
Redundancy usually hides all this from users. Traffic reroutes automatically over surviving cables, which is why a single cut rarely makes news. The danger lies in places where routes bunch together. The Red Sea corridor carries a significant share of Europe-to-Asia traffic through a narrow, shallow channel, and cuts there in early 2024 forced large rerouting. Island economies with two or three cables, or Britain's own dependencies on a limited set of landing corridors, have far less slack.
When cuts stop looking accidental
That fragility is why recent Baltic incidents alarmed governments. In October 2023 the Balticconnector gas pipeline and a nearby telecoms cable were damaged by a dragged anchor; in late 2024 the C-Lion1 cable between Finland and Germany and a Sweden-Lithuania link were severed within days of each other, with investigators tracking commercial vessels whose anchors had travelled along the seabed for tens of miles. Proving intent is hard, an anchor drag looks much the same whether careless or deliberate, and the UN Convention on the Law of the Sea gives coastal states limited powers over foreign ships damaging cables outside territorial waters, under a legal regime little changed since the 1884 cable convention.
Britain has treated the threat as real for some time. A 2017 Policy Exchange report by Rishi Sunak, then a backbencher, called cables "indispensable, insecure"; in 2023 the Royal Navy commissioned RFA Proteus, a converted offshore support vessel, as a dedicated seabed-warfare and surveillance ship, and NATO has since stood up coordination cells for critical undersea infrastructure. None of that changes the underlying arithmetic: a system the modern economy cannot function without still depends on unarmoured glass tubes, a small club of ships, and the hope that most anchors are dropped honestly.
