Underwater robot (AUV / ROV)

Ninety-five per cent of the ocean floor has never been seen by human eyes. It is too deep for divers, too hostile for unprotected submarines, and too vast to survey by any technology available a century ago. Yet we have mapped nearly all of the Moon's surface. We know less about the bottom of our own ocean than we do about the surface of Mars.

Underwater robots exist to change that — and to do dozens of practical jobs in the sea while they're at it.

Two families: ROV and AUV

Underwater robots split into two fundamentally different types based on who — or what — is making the decisions.

A ROV (Remotely Operated Vehicle) is connected to a surface ship or platform by an umbilical tether — a cable that carries power down and data up. A human pilot, watching live video, controls the ROV's thrusters, cameras, and manipulator arms in real time. The tether is both its lifeline and its leash: a ROV can work at any depth the cable reaches, but it cannot range far from the ship.

An AUV (Autonomous Underwater Vehicle) carries its own batteries, its own navigation computer, and executes a pre-programmed mission plan entirely on its own. No tether, no live human control — once it submerges, it is on its own until it resurfaces. This allows AUVs to travel hundreds of kilometres, survey large areas of the seabed, or descend to depths where a cable would be impractically long.

Why underwater robotics is uniquely hard

In the ocean, nearly every technology used by land robots stops working. GPS signals do not penetrate water. Radio waves fade within metres. Cameras struggle in the dark, particle-laden deep sea. Pressure at depth is crushing — at 6,000 metres, it is 600 times atmospheric pressure, enough to crumple an unprotected metal canister. Salt water corrodes electronics. Currents move unpredictably.

Navigation underwater relies on acoustic positioning (using sound waves to triangulate location), inertial measurement units (accelerometers that track motion from a known starting point), and Doppler velocity logs (measuring speed relative to the seabed by bouncing sound off it).

A real example

ROV Jason, operated by the Woods Hole Oceanographic Institution (WHOI), has spent thousands of hours exploring hydrothermal vent communities, ancient shipwrecks, and deep-sea ecosystems that no human has ever reached. Its two manipulator arms can collect rock samples, take precise measurements, and deploy instruments. It operates at up to 6,500 metres depth, where the pressure would instantly kill an unprotected diver.

What they do

Underwater robots inspect oil and gas pipelines and offshore wind turbine foundations (most subsea infrastructure is now inspected almost entirely by ROVs). They survey the seabed before undersea cable routes. They recover flight recorders from crashed aircraft. AUVs map the Arctic seafloor under sea ice, monitoring changes in an era of rapid climate shifts.

The deepest point in the ocean — the Challenger Deep in the Mariana Trench — has been visited by more robots than humans.