What lies beneath the waves? It’s an age-old question since the days when sailors feared mythical sea monsters. These days the threat from submarines and new autonomous underwater drones is all too real.

What needs protecting is traditional maritime shipping but there is a new emphasis on underwater cables that link the digital world across oceans. Near future vulnerabilities may include underwater data centers as the Trump Administration proposes to build two each off the coasts of Maine and Alaska.

The UK said this week it will spend £90 million to create a surveillance network called Atlantic Net that would marry unmanned drones, underwater sensors and AI to detect submarines and other suspicious activity near shipping routes, communications cables and energy networks. Atlantic Net brings various sensors under one umbrella and aims to provide quicker alerts to the UK’s submarine-hunting warships and Astute-class submarines. Atlantic Net is part of a larger initiative called Atlantic Bastion that links to NATO.

“The threats beneath the North Atlantic are changing, and we are changing with them,” said Luke Pollard, UK minister for defense readiness and industry. “This investment gives the Royal Navy new technology to find threats earlier and protect our critical infrastructure.”

New technology for underwater detection may include a hush-hush Optics11 technology developed by the Dutch start-up. Optics11 beams light through optic fiber to detect acoustic vibrations underwater using either static monitoring or towed array sensors. The technology is reportedly more sensitive and has greater resolution than passive sonar using piezoelectric detection. Optics11 is developing a towed array for the Royal Netherlands Navy’s Orka-class submarines. Trials are ongoing with dozens of navies.

“Every navy knows this is the technology of the future,” says Optics11 CEO Paul Heiden. Optics11 can detect an oil tanker at 100 kilometers distance, says Heiden. The Optics11 system is said to be derived from medical technology that is so sensitive it can detect a cell dividing.

The UK also is developing closer military ties with Norway for submarine detection “west of the Bear Gap,” a stretch of the Atlantic Ocean between Svalbard and Norway that’s a known route for Russian submarines. One proposal under consideration is the conversion of 10 fishing trawlers into a flotilla of autonomous vessels equipped with the latest submarine detection tech. The idea harkens back to the use of old British whalers in World War II used as sentinels for UK warships.

Meanwhile in the Pacific Ocean, China earlier this year said it is developing a “Great Undersea Wall” to detect nuclear submarines. A main element of the program appears to be an airborne transient electromagnetic (ATEM) technology that uses a helicopter towing a giant array of coils that emit signals into the water. The main challenge with ATEM is stability as high winds and blade wash can negatively affect the integrity of the data.

Underwater detection of mines has already proven to be vital in the Strait of Hormuz. The U.S. Navy is correcting a shortfall in mine detection resources by spending $53.9 million to develop two remote mine hunting modules that use high resolution imagery and AI to distinguish between potential sea mines and discarded cars, for example. To be built by Advanced Acoustic Concepts, a U.S. subsidiary of global defense giant Thales Group, the mine-hunting modules are slated for a 2029 delivery.