What Is an ROV?

A remotely operated vehicle is an underwater robot on a leash. Power and data run down a tether from a surface vessel or platform, a pilot flies it from a control van, and the whole system exists because there are jobs below the waterline that need a human decision applied through a manipulator arm.

There are more than 5,000 active ROVs in the underwater inspection market as of 2025, which makes them the largest installed base of any subsea vehicle type by a wide margin.¹

The classes

The industry splits them by capability, not size. The two track each other closely anyway.

Observation class vehicles carry a camera, lights and enough thrust to hold position in mild current. They inspect. Small ones are portable enough for two people to deploy off a workboat, and they have taken over a great deal of work that used to need a diver: hull surveys, harbour wall inspection, fish farm net checks.

Work class vehicles carry manipulator arms and tooling, and they need real power to run them. A work-class ROV draws between 100 and 250 horsepower down its umbilical. The Saab Seaeye Leopard, a compact electric work-class vehicle rated to 3,000 metres, produces over 500 kgf of forward thrust from up to eleven thrusters while carrying a 100 kg tool payload. Schilling's UHD sits in the heavier bracket, rated to 4,000 metres as standard with payload capacity up to 300 kg.

Between them sits a middle tier, usually called light work class. Small manipulator, inspection work that occasionally needs a hand.

What the tether actually does

Three jobs, and people usually only think of one.

It carries power. That is the reason work-class vehicles exist at all, because no battery pack yet built survives a twelve-hour shift running hydraulics and thrusters at that draw.

It carries data, and the bandwidth is the part that matters. Fibre in the umbilical means live high-definition video, multiple camera feeds, sonar and sensor telemetry, all arriving at the surface with no meaningful delay. An autonomous vehicle has an acoustic modem and a few hundred bits per second. The difference in what an operator can see is total.

It also physically retains the vehicle. An ROV that loses propulsion is still attached to something. An AUV that stops responding is not.

The tether management system

Dragging a kilometre of cable through the water column would use most of a vehicle's thrust fighting drag, so work-class spreads add a tether management system between the umbilical and the vehicle.

The TMS is a garage. It descends on the heavy armoured umbilical to working depth and then pays out a thin neutrally buoyant tether, and the vehicle flies on that short leash while the TMS carries the load. Without it a 3,000 metre deployment would need three times the thrust.

Who flies them

ROV pilot technicians, working shifts from a container on deck. The job is part flying and part maintenance, and the maintenance half is much larger than outsiders expect. Hydraulics leak. Connectors flood. Thrusters ingest rope.

Training runs through pilot schemes and, for vehicles working alongside divers, the certification regimes that come with IMCA membership. Simulator hours are now standard.

Where the work is

Offshore oil and gas remains the largest single market, but offshore wind is the fastest-growing, now accounting for somewhere between 18 and 29 percent of global ROV demand depending on whose definition you take.²

Beyond energy: cable route survey and repair, harbour and berth inspection, salvage, search and recovery, aquaculture net inspection, scientific sampling, naval mine countermeasures.

What is changing

Two things. Both get their own article on this site.

Hydraulic power is giving way to all-electric vehicles, which remove the oil, the leak points and a large share of the maintenance burden. And residency is changing the deployment model entirely: park the vehicle subsea permanently, run power and fibre from the platform, fly it from an onshore control room, and the surface vessel disappears from the cost line.

Neither changes what an ROV is. Both change what it costs to keep one available, which is the number that actually decides whether a job gets done.