The cable will run for more than 50,000 kilometres (31,000 miles) between the US, South Africa, India, Brazil and "other regions", Meta wrote in a blog on Friday.

Global digital communication relies on a vast network of undersea conduits, with roughly 1.2 million kilometres of cable already installed, according to a 2024 report by the US-based Centre for Strategic and International Studies (CSIS).

The links can be short hops between countries or globe-spanning systems linking multiple continents.

Each is made up of multiple pairs of fibre-optic cables in an armoured sheath that may be buried several metres under the sea bed for protection.

Data-hungry digital giants like Meta have in recent years muscled in to the world of subsea cables that was once the province of dedicated telecoms providers.

"At some point when your growth is so big and your demand volumes outweigh other people's, you're incentivised to invest yourself, cut out the middleman," said Alan Mauldin, research director at specialist data firm Telegeography.

Meta said its latest cable project represented a "multi-billion-dollar, multi-year investment" -- a relative drop in the bucket compared to the sector's tens of billions annually in planned artificial intelligence investments.

- Resilient networks -

Google and Meta's pushes, whether joining cable-building consortiums to part-own new infrastructure or going it alone, have been especially intensive given the vast appetite for data of their platforms like YouTube, Facebook or Instagram.

The new "Project Waterworth" cable will be Meta's third as a sole owner, according to Telegeography's listings -- well behind Google with 16.

Meta's first cable, "Anjana" linking the US and Spain, is set to come online early this year.

"Waterworth" is named for a late Meta employee, Gary Waterworth, who worked for five years at the US giant after a career largely spent at Alcatel Submarine Networks (ASN).

The French cable-laying firm is one of only a few worldwide capable of installing the hardware, alongside America's SubCom, Japan's NEC and China's HMN.

Platforms' motives for getting into the cable game also include directly linking their global operations and especially increasing resilience of their networks, Mauldin said.

"One new big, high capacity cable doesn't do you any good... you need to have three or four because if one goes down, two goes down, you can still route the traffic," he noted.

Every year brings around 200 incidents of damage to cables that could otherwise endanger great swaths of economic activity.

Those can stem from natural causes like underwater landslides and tsunamis, or human ones like dragging ship anchors or fishing equipment.

- AI stoking data traffic -

Cables can also be targets for deliberate sabotage and spying.

NATO in January launched dedicated patrols of the Baltic Sea after suspected attacks on telecom and power cables that experts and politicians have blamed on Russia.

Meta's "Waterworth" route avoids geopolitical hotspots like the South China Sea, subject to dispute between Beijing and its neighbours, and the Red Sea, Mauldin pointed out.

The Facebook owner also said the cable project would provide "the abundant, high speed connectivity needed to drive AI innovation".

"AI is the hottest issue in the industry right now," Telegeography's Mauldin said, although its impact on demand for cables and bandwidth remains unclear.

"Training" new AI models could require piping large amounts of data quickly to the sites of computing clusters around the globe, he noted, while AI inference -- its actual responses to users' prompts -- will also have transmission requirements.

"A lot of companies could be emerging in this space, but the big companies, the big hyperscalers seem to have a really big advantage" with existing data centres and networks, Mauldin said.

He pointed to the examples of OpenAI -- massively backed by Microsoft, another player with stakes in undersea cables -- and Anthropic, backed by Google and Amazon.

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