Underwater Robots (AUV & ROV): The Ultimate Guide

Salt water is the most hostile place we routinely send robots. It crushes, it corrodes, it blinds. At 1,000 meters the pressure on a housing is roughly 100 atmospheres, about 1,450 psi, enough to implode a thin-walled aluminum tube like a soda can. Radio does not travel through it, so GPS stops at the surface and every navigation trick that a drone or a car relies on is gone the moment the vehicle submerges. Light attenuates in meters, so cameras see a few body-lengths on a good day and nothing in the plume of silt a thruster kicks up. The one signal that does propagate, sound, travels at roughly 1,500 m/s, a million times slower than radio, so a command to a vehicle two kilometers down arrives more than a second later and comes back a second after that. Everything about underwater robotics is shaped by those four facts: pressure, no GPS, no radio, slow sound.

Two machine architectures dominate the field, and they sit at opposite ends of a tradeoff. The ROV (remotely operated vehicle) is tethered: a cable carries power and high-bandwidth data down from a ship or a shore station, and a human pilot flies it with a joystick, watching live video. The AUV (autonomous underwater vehicle) cuts the cord: it carries its own battery, runs its own mission, and comes back hours or days later with data. The tether is both the ROV's strength (unlimited power, real-time control, no autonomy required) and its leash (drag, snag risk, and a support ship burning fuel above it). The AUV trades away real-time human judgment for range and the ability to survey vast areas cheaply. Gliders form a third camp, sacrificing speed and control almost entirely to buy weeks or months of endurance.

This guide treats the underwater robot as what it is: a pressure vessel full of electronics that has to navigate blind, sense through murky water, and survive corrosion, all while a ship overhead costs tens of thousands of dollars a day. We work through the ROV/AUV/glider split, the physics of the environment, how these vehicles navigate without satellites, propulsion and buoyancy, the sonar-first sensing suite, power and endurance, the applications that pay for all of it, the companies that build the hardware, and where the field is heading.

The take: Underwater robotics is defined by what does not work. GPS, radio, and long-range vision all fail underwater, so the entire discipline is about navigating and communicating with the one physical channel that survives, sound, plus dead-reckoning good enough to bridge the gaps. An ROV solves this by keeping a human and a fat data cable in the loop; an AUV solves it by carrying a precision inertial navigation system fused with a Doppler velocity log and occasional acoustic fixes. Choose the tether when you need real-time judgment and power at a fixed worksite; choose autonomy when you need to cover distance or area that a cable cannot reach. Everything downstream, the housing rating, the thruster count, the sonar choice, the battery chemistry, follows from that one decision and the depth you must reach.

Companion reading: drone navigation, GNSS & RTK, robot sensors, SLAM & localization, robot power & batteries, robot actuators, and robot wiring, cables & connectors.

Table of contents

1. Key takeaways
2. ROV, AUV, glider: the three architectures
3. The environment: pressure, corrosion, light, sound
4. Navigation without GPS: INS, DVL, USBL, LBL
5. Propulsion, buoyancy, and station-keeping
6. Sensing: sonar first, cameras second
7. Power and endurance
8. Applications and unit economics
9. The players and their hardware
10. The maker tier: Blue Robotics and open ROVs
11. Where the field is heading
12. Frequently asked questions

ROV, AUV, glider: the three architectures

Everything in underwater robotics starts with whether the vehicle is on a leash.

An ROV is tethered to a surface vessel or platform by an umbilical: a bundle of copper power conductors and fiber-optic data lines wrapped in a strength member. That cable is the whole design philosophy. Power comes down it, so the vehicle can drive heavy thrusters, hydraulic manipulators, cutting tools, and bright lights without carrying a battery. Full-motion video and sensor data come up it in real time, so a human pilot in a control van flies the vehicle by joystick and does the reasoning. The ROV never has to be autonomous because a person is always in the loop. ROVs split into classes by size and power: observation-class or micro-ROVs (a few kilograms to tens of kilograms, camera-and-lights inspection), light work-class, and work-class (thousands of kilograms, hydraulic manipulators, hundreds of horsepower, working on oil-and-gas infrastructure at 3,000+ meters). The tether's cost is drag, weight, and snag risk, plus the expensive ship or tether-management system that must stay on station above the vehicle for the entire dive.

An AUV carries its own energy and intelligence and runs untethered. A survey AUV is typically a torpedo shape, streamlined for efficient transit, with a single stern thruster and control fins. It is programmed with a mission (a lawnmower survey pattern over a patch of seafloor, say), launched, and recovered hours or days later. Between launch and recovery it is on its own: no one is flying it, and for most of the mission no one can even talk to it beyond terse acoustic status pings. That autonomy is what lets one vehicle map hundreds of square kilometers or transit hundreds of kilometers, distances no tether reaches. The price is that everything must be trusted to the vehicle's navigation and mission logic, and if something goes wrong you find out on recovery, or not at all. A distinct sub-type, the hovering AUV, adds thrusters for the low-speed, precise-positioning work of inspection, blurring the line with the ROV.

A glider is an AUV that has almost no propulsion. It changes its buoyancy with a small pump (pushing oil into or out of an external bladder, or moving a piston) to sink and rise, and wings convert that vertical motion into slow forward glide, sawtoothing through the water column at a fraction of a knot. Gliders move internal battery mass to pitch and roll. Because the buoyancy pump runs only briefly per dive cycle, a glider sips power and stays out for weeks to months, covering thousands of kilometers. They carry oceanographic sensors (temperature, salinity, oxygen, currents) and surface periodically to phone home over satellite. Slocum, Seaglider, and Spray are the classic designs. The tradeoff is stark: near-zero speed and almost no maneuvering control, in exchange for endurance nothing else matches.

	ROV (work-class)	AUV (survey)	Glider
Tether	Yes (power + fiber)	No	No
Control	Human pilot, real-time	Preprogrammed / autonomous	Preprogrammed, minimal
Endurance	Ship-limited (days)	Hours to a few days	Weeks to months
Speed	Hover to ~3 kn	~3 to 6 kn	~0.5 kn
Power source	Surface (unlimited)	Onboard battery	Onboard battery
Typical job	Intervention, inspection at a worksite	Wide-area mapping, survey	Long-duration ocean sensing
Payload power	High (tools, manipulators)	Moderate	Very low (sensors only)

Rule of thumb: If a job needs a manipulator, a cutting tool, or a human deciding what to do next while looking at live video, it is an ROV job. If it needs distance or area, it is an AUV job. If it needs to stay out for a month measuring the water, it is a glider job.

The environment: pressure, corrosion, light, sound

Four physical facts drive every design decision.

Pressure. Water adds roughly one atmosphere for every 10 meters of depth, so pressure climbs fast: about 100 atm at 1,000 m, 600 atm at 6,000 m, and over 1,100 atm in the deepest trenches near 11,000 m. Anything holding a one-atmosphere air pocket, the electronics housing, the camera dome, a battery can, is a pressure vessel that must resist implosion, and the wall thickness (and therefore weight) grows with depth rating. Two design schools split here. The traditional approach is a rigid one-atmosphere housing: a titanium or aluminum tube with domed or flat end caps, rated to a crush depth with a safety margin. The alternative is pressure tolerance: fill the enclosure with incompressible oil so internal and external pressure equalize, and there is nothing to crush. Oil-filled, pressure-balanced electronics and oil-filled thrusters let designers skip the heavy vessel entirely, which is how many deep vehicles keep weight down. Syntactic foam (hollow glass microspheres in resin) provides buoyancy that survives depth because it barely compresses.

Corrosion and biofouling. Salt water is an electrolyte, so any two dissimilar metals in contact form a galvanic cell and one of them corrodes. Structures use titanium (nearly immune), anodized aluminum, and engineering plastics (acetal, HDPE, PVC). Sacrificial zinc or aluminum anodes are bolted on to corrode preferentially and protect the rest. Anything left in the water for weeks grows biofilm and then barnacles and weed, which add drag and foul sensors, so persistent vehicles and moored equipment carry antifouling coatings, copper guards, or wipers.

Light. Water absorbs and scatters light quickly, and it eats the red end of the spectrum first, which is why deep footage looks blue-green. Practical camera range is a few meters even with powerful lights, and lights make it worse in turbid water by illuminating suspended particles, the underwater equivalent of driving with high beams in fog. This is the fundamental reason underwater robots lead with sonar, not cameras.

Sound. Sound is the only signal that carries any useful distance underwater, and it is slow: about 1,500 m/s, varying with temperature, salinity, and pressure. That variation bends sound rays (refraction), creating shadow zones and range errors, which is why acoustic positioning systems apply a sound-speed profile. The slow speed sets a hard latency floor: a round trip to a vehicle at 3,000 m is about four seconds, so real-time acoustic "flying" is impossible. And the channel is narrow: acoustic modems manage kilobits per second at best over long range, far too little for video. Sound is simultaneously the enabler (it is why we can navigate and communicate at all) and the constraint (it is slow and thin).

Safety rule: Depth rating is not a marketing number. A housing rated to 300 m implodes catastrophically deeper, releasing energy that can destroy neighboring components. Always dive well inside the rating, pressure-test housings after any O-ring service, and treat a flooded compartment on recovery as a full incident investigation, not a wipe-down.

Navigation without GPS: INS, DVL, USBL, LBL

This is the hardest problem in the field and the one that most separates a serious vehicle from a toy. GPS needs radio from satellites, and radio dies within meters of the surface. So an underwater robot navigates by dead reckoning, estimating where it is by integrating how it has moved, and then bounding the accumulating error with whatever absolute fixes it can get. The toolkit mirrors the fusion problem covered in SLAM & localization, adapted to a world with no satellites.

Inertial navigation system (INS). At the core is an inertial measurement unit: gyroscopes measuring rotation and accelerometers measuring acceleration on three axes. Integrate acceleration once for velocity, twice for position, and track orientation from the gyros. The problem is drift: tiny sensor biases integrate into a position error that grows without bound, and a bare IMU can be hundreds of meters off within minutes. High-end subsea INS use fiber-optic gyros (FOG) or ring-laser gyros, far more stable than the MEMS parts in a phone, but even they drift if left to integrate alone. The INS is the fast, smooth backbone of the estimate, and it needs help.

Doppler velocity log (DVL). The DVL is the single most important aiding sensor. It points four acoustic beams at the seafloor and measures the Doppler shift of the returns to compute the vehicle's velocity over the ground in three axes. Feeding true ground speed into the navigation filter dramatically bounds the INS drift: instead of double-integrating noisy acceleration, the filter is corrected by a direct velocity measurement many times a second. An INS aided by a good DVL holds position error to roughly 0.05 to 0.1% of distance traveled, so a vehicle that runs 10 km comes back with an error on the order of 5 to 10 meters. The catch is that the DVL needs to be within "bottom lock" range of the seafloor (tens to a few hundred meters depending on frequency); above that it can track the water layer instead, which is less accurate.

Acoustic positioning: USBL and LBL. To get absolute position (true latitude and longitude in the world, beyond the relative distance travelled from the start) the vehicle needs acoustic fixes from a known reference.

• USBL (Ultra-Short Baseline) puts a transducer array on the support ship's hull. It measures the range and bearing to a transponder on the vehicle by timing an acoustic round trip and comparing phase across the closely spaced array elements. Combined with the ship's own GPS and attitude, it yields the vehicle's absolute position. USBL is quick to deploy (nothing on the seabed) but its accuracy degrades with depth and depends on the ship's motion reference.
• LBL (Long Baseline) drops an array of transponder beacons on the seafloor at surveyed positions, forming a baseline hundreds of meters to kilometers wide. The vehicle ranges to several of them and trilaterates its position, exactly like GPS but with acoustic beacons on the bottom instead of satellites in orbit. LBL gives the highest accuracy (down to centimeters to meters over a work area) and is independent of depth, but it requires the slow, expensive step of deploying and calibrating the beacon field first.

In practice a survey AUV fuses all of this: an INS as the backbone, a DVL for velocity aiding, a pressure sensor for precise depth, an acoustic modem/USBL for occasional absolute fixes, and a GPS fix taken every time it surfaces to reset the whole estimate. The fusion is a Kalman filter that weights each source by its trusted accuracy, the same architecture that runs on drones and cars, just with acoustics standing in for satellites.

War story: An AUV finishes a clean 20 km survey, and the mosaic of the seafloor looks perfect except that a pipeline the operator knows is straight appears to gently bow across the map. The vehicle navigated well; the bow is a sound-speed error. The DVL and USBL both assume a sound velocity to turn travel time into distance, and a wrong sound-speed profile stretches or shrinks the whole survey subtly. The fix is a proper sound-velocity cast before the mission, not a better vehicle. Underwater, the medium is part of the instrument.

Propulsion, buoyancy, and station-keeping

Underwater vehicles are trimmed to float near neutral buoyancy: they weigh almost exactly what they displace, so gravity and buoyancy nearly cancel and the propulsion system only has to fight drag and provide control forces, not hold the vehicle up. Ballast (fixed weights) and syntactic foam (fixed lift) set the gross trim; a slight positive buoyancy is common so a dead vehicle floats to the surface to be recovered. Thrusters do the rest.

Thrusters are propellers driven by electric motors, and underwater they are almost always brushless DC motors run in oil-filled, pressure-balanced housings or fully flooded and potted, because a sealed one-atmosphere motor can would have to be a heavy pressure vessel. For deep motor and drive detail see robot actuators. A ducted propeller (a nozzle around the prop) increases thrust at low speed and protects the blades. The number and arrangement of thrusters defines the vehicle's maneuverability:

• A torpedo survey AUV typically has a single stern thruster for forward drive plus movable fins or a vectored stern for steering. It is efficient in a straight line and turns like a slow aircraft, which is all a lawnmower survey needs.
• A work-class ROV carries six to eight thrusters arranged to give control in all directions plus hover: it must hold station precisely against current while a manipulator does delicate work. Vectored horizontal thrusters plus vertical thrusters let it translate sideways, hold heading, and maintain depth simultaneously.

Station-keeping in current is a real control challenge. Subsea currents push the vehicle and drag the tether, and an ROV pilot (or an autopilot in "auto-position" and "auto-heading" modes) constantly trims the thrusters to stay put. The tether itself is often the dominant disturbance: current on a hundreds-of-meters umbilical exerts far more force than on the compact vehicle, which is why work-class systems use a tether management system (TMS), a "garage" that lowers near the worksite and pays out only a short, slack length of tether to the vehicle, isolating it from the drag of the full umbilical.

Gliders deserve a separate mention because they have no thruster at all. A glider's "propulsion" is a buoyancy engine: a pump moves a small volume of oil to an external bladder to become positively buoyant and rise, then pulls it back to sink, and fixed wings turn that vertical motion into forward glide. Pitch and roll are controlled by shifting internal battery mass. It is the most energy-frugal way to move through water, and the reason gliders endure for months.

Sensing: sonar first, cameras second

Because light fails, underwater perception leads with acoustics. Sonar is to underwater robots what lidar and cameras are to a self-driving car, and the different sonar types map to different jobs.

• Multibeam echosounder (bathymetry). A fan of acoustic beams measures the depth to the seafloor across a wide swath beneath the vehicle, building a high-resolution 3D terrain map. This is the workhorse of hydrographic survey and the reason AUVs can map the seabed faster and closer than a ship on the surface.
• Side-scan sonar (imagery). A transducer on each side sweeps grazing acoustic beams outward and records the intensity of the echo, producing a photograph-like acoustic image of the seafloor texture and any objects on it. Side-scan is how you find shipwrecks, mines, pipelines, and debris across a wide swath. Higher frequency gives finer resolution but shorter range, so survey vehicles trade the two by mission.
• Synthetic aperture sonar (SAS). By coherently combining returns as the vehicle moves, SAS synthesizes a much larger effective aperture and delivers centimeter-scale imagery at long range, resolution roughly independent of distance. It is the high end of mine-hunting and detailed survey, and it demands excellent navigation (the platform's own motion must be known precisely to combine the pings).
• Forward-looking sonar. A sonar aimed ahead detects obstacles and structures for navigation and collision avoidance in low-visibility water, and imaging sonars give a live acoustic "video" for close-in inspection where cameras see nothing.
• Sub-bottom profiler. A low-frequency source penetrates the seabed and images the sediment layers below it, used for geotechnical survey, cable-route planning, and archaeology.

Cameras still matter for close-range work: high-definition and stereo cameras on ROVs give the pilot the detailed visual an inspection or intervention needs, paired with powerful LED arrays. Laser scanners and structured-light systems produce fine 3D models of subsea structures at very short range. But vision is a close-quarters tool, used within a few meters, while the vehicle relies on sonar to get there and to build the big picture. The rest of the suite mirrors any robot: a pressure sensor for precise depth, a compass/AHRS, conductivity-temperature-depth (CTD) probes for the water properties (which also feed the sound-speed correction navigation needs), and mission-specific payloads like magnetometers, methane sniffers, or cathodic-protection probes. For the general sensor treatment see robot sensors.

Power and endurance

Power is where the ROV/AUV split shows its consequences most clearly.

An ROV takes power down the tether, so endurance is effectively unlimited: the vehicle can work a full shift and the limit is the ship's schedule and crew, not a battery. This is why heavy intervention (hydraulic manipulators, dredging, cutting) is ROV territory. The cost is that the ship must stay on station the whole time, and offshore vessels run tens of thousands of dollars per day, often well into six figures for a large construction vessel with a work-class ROV spread. Every minute the ROV is down, that meter is running.

An AUV carries its own battery, so its mission is bounded by energy. Modern survey AUVs use lithium-ion packs (the same chemistry family covered in robot power & batteries) in pressure-tolerant, often oil-filled or individually pressure-rated housings, and typical endurance runs from a handful of hours for small vehicles to 20 to 100 hours for large survey AUVs like the Kongsberg HUGIN class. Endurance scales with hull volume (more battery) and inversely with speed (drag rises with the square of speed), so survey AUVs cruise at an efficient 3 to 4 knots. Some large or long-endurance vehicles use higher-energy chemistries; historically aluminum-oxygen and other semi-fuel-cell systems pushed endurance to days, and hydrogen fuel cells have been flown in extra-large vehicles. Gliders, sipping power from the buoyancy engine, run on lithium primary or rechargeable packs for weeks to months and thousands of kilometers.

The recharge and turnaround problem shapes operations. An AUV that runs 24 hours then needs hours of recharge and data offload on deck. Subsea docking stations address this: a resident vehicle lives in a seabed garage, undocks to do a job, and returns to recharge inductively and dump data over a high-bandwidth link, staying deployed for months without a ship. Resident and "vehicle-as-a-service" models built on docking are one of the biggest operational shifts in the field.

Vehicle	Energy source	Typical endurance	Typical speed
Observation ROV	Tether (surface)	Ship-limited	0 to 3 kn
Work-class ROV	Tether (surface)	Ship-limited	0 to 3 kn
Survey AUV	Onboard Li-ion	10 to 100 h	3 to 6 kn
Hovering AUV	Onboard Li-ion	Hours	0 to 2 kn
Glider	Onboard (buoyancy engine)	Weeks to months	~0.5 kn

Applications and unit economics

The demand that funds underwater robotics is concentrated in a few sectors, and offshore energy is by far the largest.

Offshore energy inspection and intervention. Oil-and-gas platforms, subsea wellheads, pipelines, and risers need constant inspection and occasional repair, all at depths and durations no diver can reach. Work-class ROVs do drilling support, valve operation, and construction; observation ROVs and AUVs do pipeline surveys, running along thousands of kilometers of pipe checking for spans, leaks, and cathodic-protection health. Offshore wind has become a fast-growing second market: turbine foundations, scour protection, and inter-array cables all need survey and inspection, and the sheer number of structures in a wind farm favors efficient autonomous vehicles.

Hydrographic and geophysical survey. Charting the seafloor for navigation, cable and pipeline route planning, and offshore construction. AUVs flying close to the bottom with multibeam and side-scan produce far higher resolution than a surface ship, which matters for engineering-grade survey.

Defense. Mine countermeasures (MCM) is the signature military application: AUVs with side-scan and synthetic aperture sonar hunt for mines, keeping sailors and ships out of the danger area. The REMUS family is widely used for exactly this. Larger programs push toward big autonomous vehicles for long-range surveillance, seabed warfare, and undersea logistics.

Science. Oceanographic research uses gliders for sustained water-column measurement (temperature, salinity, oxygen, carbon), AUVs for under-ice survey and deep mapping, and ROVs on research ships for deep-sea biology and geology. Institutions like Woods Hole and MBARI have driven much of the vehicle innovation.

Aquaculture and coastal. Fish-farm net inspection, mooring checks, and hull cleaning are a growing use for small ROVs, where a light, cheap vehicle replaces a diver for routine visual jobs.

The economics come down to comparing the robot against its alternatives: a saturation diver (extremely expensive and dangerous, depth-limited), a manned submersible (costly, limited), or a surface ship dragging sensors (slow, low-resolution). An AUV that surveys a pipeline in one pass replaces days of slower work and removes people from hazard. The dominant line item almost everywhere is the support vessel, so the strategic direction of the whole industry is to reduce or remove the ship: over-the-horizon control, uncrewed surface vessels launching the underwater robot, and resident subsea systems that need no ship at all.

Rule of thumb: In offshore work the vehicle is rarely the expensive part. The day rate of the ship and crew above it dominates the cost, so anything that shortens the dive, removes the tether-management overhead, or eliminates the ship entirely is where the money and the engineering go.

The players and their hardware

The industry splits into ROV builders, AUV builders, large-vehicle and surface-autonomy players, and the maker tier.

ROVs. Saab Seaeye is a leading builder of electric work-class and observation ROVs. Oceaneering is the largest ROV operator, running a huge fleet of work-class vehicles (its Millennium and Nexxus classes) in service to offshore energy, and it also builds AUVs. Forum Energy Technologies (Perry/Sub-Atlantic) and Kystdesign are significant ROV manufacturers. Historically many work-class ROVs were hydraulic; the trend is toward all-electric vehicles for efficiency, controllability, and lower maintenance.

Survey AUVs. Kongsberg builds the HUGIN family, the benchmark deep-water survey AUV, carrying HISAS synthetic aperture sonar and rated to thousands of meters, plus the smaller MUNIN. HII (Huntington Ingalls, which acquired Hydroid in 2020) builds the REMUS family, from the man-portable REMUS 100 up through larger MCM and survey vehicles, the workhorse of naval mine countermeasures. Teledyne Marine (which includes Gavia and the Webb Slocum glider) spans small AUVs, gliders, DVLs, and sonars. ECA Group builds AUVs and MCM systems.

Large and extra-large vehicles. Boeing and HII developed Orca, an extra-large uncrewed undersea vehicle for the US Navy, capable of long autonomous transits with a modular payload bay, the kind of vehicle meant to operate for weeks without a mother ship. Anduril (which acquired Dive Technologies) is pushing autonomous undersea vehicles for defense. Cellula Robotics builds long-range hydrogen-fuel-cell AUVs.

Surface autonomy and hybrids. Saildrone builds wind-and-solar-powered autonomous surface vehicles that carry sensors for ocean data, defense, and mapping missions lasting months, an adjacent approach that solves endurance by staying on the surface where it can harvest energy and use satellite comms. Uncrewed surface vessels are increasingly paired with underwater robots as their launch, recovery, and communications relay.

Navigation and sensor suppliers. The subsystems are their own industry: Sonardyne, iXblue/Exail, and Kongsberg for INS and acoustic positioning (USBL/LBL); Teledyne RDI and Nortek for DVLs; Kongsberg, EdgeTech, Klein, and Norbit for sonars; and SubConn/MacArtney and Teledyne Impulse for wet-mateable connectors. A vehicle integrator assembles these into a platform, and the wiring and connector discipline is unusually demanding because every penetration is a potential flood path.

Robotics leaderboards on data.robo2u.com track the humanoid, quadruped, and drone categories most closely; the marine sector is more fragmented and defense-heavy, so vehicle specs there come largely from the manufacturers named above.

The maker tier: Blue Robotics and open ROVs

A decade ago building an underwater robot meant a large budget and machine-shop access. Blue Robotics changed the entry point by manufacturing affordable, depth-rated components: the T200 thruster (a brushless motor in a flooded, pressure-tolerant housing that became a de facto standard), penetrators and enclosures, pressure sensors, and the BlueROV2, a compact observation-class ROV kit rated to a few hundred meters that thousands of hobbyists, researchers, and small commercial operators use. The BlueROV2 typically runs the open-source ArduSub firmware (part of the ArduPilot project), giving it stabilized flight, depth and heading hold, and integration with the QGroundControl interface, the same autonomy stack lineage used across drones and rovers.

This tier matters beyond hobbyists. It put a capable, repairable, sub-$10k ROV in reach of aquaculture operators, university labs, search-and-rescue teams, and inspection contractors who could never justify a work-class system. The open firmware means the vehicles are hackable and extensible, which has seeded a generation of engineers who learned marine robotics on a BlueROV2 before moving to the professional systems. The lesson mirrors what happened in aerial drones: a low-cost open platform expands the whole field by lowering the first step. Chinese consumer-ROV makers (QYSEA and others) have similarly pushed small camera ROVs into the recreational and light-commercial market.

Where the field is heading

Several trends are reshaping underwater robotics through the late 2020s.

Getting rid of the ship. The support vessel is the cost, so the industry is attacking it from every angle: uncrewed surface vessels that launch and recover the underwater robot and relay its data, over-the-horizon piloting where an operator onshore flies a resident ROV through a satellite link, and resident subsea systems where a vehicle lives in a seabed docking station for months, undocking on command and recharging inductively. Removing people and ships from the offshore worksite is the central economic story.

More autonomy, less piloting. ROVs are gaining autopilot functions (auto-track a pipeline, auto-fly an inspection path) so one operator supervises rather than joysticks every move, and AUVs are gaining onboard perception to adapt a mission in real time (re-survey an interesting target, avoid an obstacle) instead of blindly executing a preplanned track. The reinforcement-learning and perception techniques maturing elsewhere in robotics are slowly reaching a domain that has been conservative because failures are expensive and unrecoverable.

Better navigation and comms. Terrain-relative navigation (matching live sonar to a prior seabed map to fix position without acoustic beacons) and improving acoustic and optical modems are chipping away at the no-GPS, low-bandwidth constraints. Optical (blue-green laser) communication offers megabit links at short range for docking and data offload.

Manipulation and intervention autonomy. Autonomous and semi-autonomous manipulation (turning a valve, connecting a hose, cleaning a structure) is a hard frontier because it combines the underwater environment with contact-rich control. Progress here would let vehicles do intervention work that today requires a skilled pilot on a work-class ROV.

Larger autonomous vehicles. Extra-large uncrewed undersea vehicles for defense and, eventually, commercial subsea logistics and long-range survey represent the scaling-up end: vehicles that operate for weeks, carry modular payloads, and change what a single mission can cover.

The through-line is constant. Every advance is measured against the same four adversaries the field started with: pressure, no GPS, no radio, and slow sound. The winners are the teams that navigate blind the most accurately, survive depth the most cheaply, and keep the expensive ship on the horizon or gone entirely.

Frequently asked questions

What is the difference between an ROV and an AUV? An ROV is tethered to a surface vessel by a cable that carries power and data, and a human pilot flies it in real time. An AUV is untethered, carries its own battery, and executes a mission autonomously. The ROV trades range for real-time control and unlimited power; the AUV trades human judgment for the ability to cover distance and area no cable can reach.

Why can't underwater robots just use GPS? GPS relies on radio signals from satellites, and radio is absorbed within a few meters of entering water. So underwater vehicles navigate by dead reckoning (an inertial navigation system integrating motion, aided by a Doppler velocity log measuring speed over the seafloor) and correct that estimate with acoustic positioning (USBL or LBL) and a GPS fix taken each time they surface.

How deep can these robots go? Depth ratings cluster around the applications: coastal and inspection vehicles at 300 m, offshore and survey vehicles at 1,000 to 3,000 m, and full-ocean vehicles at 6,000 m, which covers about 98% of the seafloor. Specialized vehicles have reached the deepest trenches near 11,000 m. The rating is set by the housing's resistance to implosion, and wall thickness and weight grow with depth.

How do underwater robots communicate? Over acoustic modems, which use sound because it is the only signal that travels usefully underwater. The bandwidth is low (kilobits per second) and latency is high (multi-second at depth because sound travels at only about 1,500 m/s), so you cannot stream video acoustically. That bandwidth limit is exactly why ROVs keep a fiber-optic tether for live video and AUVs must run autonomously.

What is a Doppler velocity log and why does it matter? A DVL points acoustic beams at the seafloor and measures the Doppler shift of the echoes to compute the vehicle's velocity over the ground. Feeding true ground speed into the navigation filter bounds the drift of the inertial system, taking position error from hundreds of meters down to roughly 0.05 to 0.1% of distance traveled. It is the single most important aiding sensor for accurate underwater navigation.

Why do underwater robots use sonar instead of cameras? Water absorbs and scatters light, so cameras see only a few meters even with powerful lights, and lights make turbid water worse by illuminating suspended particles. Sound travels far, so sonar (multibeam, side-scan, synthetic aperture, forward-looking) is the primary way these vehicles map the seabed and detect objects. Cameras are used for close-range detail once the vehicle is already there.

What powers a work-class ROV versus an AUV? A work-class ROV draws power down its tether from the surface, so it can run heavy hydraulic manipulators and tools indefinitely, limited only by the ship's schedule. An AUV carries onboard lithium-ion batteries and runs from several hours to around 100 hours depending on size and speed. Gliders use a tiny buoyancy-engine pump and endure for weeks to months.

Who are the main manufacturers? Saab Seaeye and Oceaneering lead ROVs; Kongsberg (HUGIN) and HII (REMUS, formerly Hydroid) lead survey AUVs; Teledyne Marine spans small AUVs and gliders; Boeing/HII Orca and Anduril push large defense vehicles; Saildrone leads autonomous surface vehicles; and Blue Robotics dominates the affordable maker and light-commercial tier with the BlueROV2 and its thrusters.

What is the biggest cost driver in commercial underwater operations? The support vessel. Offshore ships run from tens of thousands to well over a hundred thousand dollars a day, dwarfing the vehicle itself. That is why the whole industry is working to shorten dives, remove the tether-management overhead, pilot resident vehicles from shore, and ultimately eliminate the crewed ship with uncrewed surface vessels and seabed docking stations.