Reference
Maritime terms and definitions
Maritime terms: ships and naval architecture, maritime law and security, undersea vehicles and naval warfare, underwater acoustics and sonar, navigation and timing, ocean engineering, diving physiology and aquaculture. These are general reference definitions, not tied to any one report.
200 of 200 terms shown
A
- Additional secondary factor (ASF)
- The extra delay a Loran signal picks up crossing land of varying conductivity. It must be mapped and corrected for accurate positioning.
- Allan deviation (Allan variance)
- A measure of how stable a clock or sensor is over different averaging times, used to compare gyroscopes, accelerometers and oscillators.
- Ambient noise (ocean ambient noise)
- Background sound in the sea from waves, rain, shipping and marine life, against which a sonar must detect targets.
- Anti-submarine warfare (ASW)
- Finding, tracking and attacking enemy submarines, mainly with sonar from ships, aircraft, submarines and sonobuoys.
- Antifouling coating (antifouling, anti-fouling paint)
- Hull paint that stops barnacles, weed and slime from attaching, cutting drag and fuel use.
- Aquaculture (fish farming, mariculture)
- Farming fish, shellfish and seaweed in controlled conditions, on land or in open water. Since 2022 it has produced more aquatic animals than wild capture fisheries.
- Aquaculture Stewardship Council (ASC, ASC certification)
- An independent body that certifies responsibly farmed seafood against environmental and social standards.
- Aquaponics
- A combined system in which fish waste fertilizes plants grown in water, and the plants clean the water for the fish.
- Atom interferometry (atom interferometer, cold-atom interferometry, matter-wave interferometry)
- Measuring acceleration or rotation by splitting a cloud of laser-cooled atoms into matter waves and recombining them; the interference pattern reveals motion with very low drift.
- Atomic clock (chip-scale atomic clock, CSAC, optical clock, optical atomic clock)
- A clock that keeps time from the steady frequency of atomic transitions. Chip-scale versions let vehicles hold accurate time without satellites; optical clocks are more precise still.
- Attritable (attritable aircraft, attritable systems)In Aerospace
- Cheap enough that losing some in combat is acceptable, yet designed to be reused if they survive. Attritable aircraft sit between expendable munitions and costly crewed jets.
- AUKUS Pillar II (AUKUS, Pillar II, Pillar 2, AUKUS Pillar 2)
- The advanced-capabilities track of the Australia-UK-US security pact, covering undersea autonomy, quantum technologies, AI and hypersonics. Pillar I covers nuclear-powered submarines for Australia.
- Autonomous underwater vehicle (AUV, AUVs)
- An untethered robot submarine that runs a mission on its own, without continuous human control, surfacing or using acoustic links to report.
- Auxiliary engine (auxiliary generator, genset)
- A ship's smaller engine-generator set that supplies onboard electricity, separate from the main propulsion engine. It often runs in port unless shore power is used.
B
- Ballast (ballast water, ballast tanks)
- Water or other weight carried low in a ship to keep it stable and trimmed when it is lightly loaded.
- Bathymetry (bathymetric survey, seafloor mapping)
- The measurement and mapping of water depth and seafloor shape, mainly with ship-mounted multibeam sonar.
- Battery energy storage system (BESS, battery storage, grid battery)In Batteries
- A stationary installation of batteries, inverters, controls and safety equipment that stores electricity for later use. Most new grid-scale systems use LFP cells in shipping-container units.
- Beam and draft (beam, draft, draught)
- A ship's beam is its width at the widest point; its draft is the depth of hull below the waterline. Both limit which ports, canals and berths it can use.
- Benthic (benthos, benthic fauna)In Minerals
- Relating to the seafloor and the animals that live on or in it.
- Biofilter (biological filter, nitrification, nitrifying bacteria)
- A filter colonized by bacteria that convert toxic ammonia from fish waste into nitrite and then much less harmful nitrate, a process called nitrification.
- Biofloc technology (BFT, biofloc)
- An aquaculture method that keeps microbial clumps in the water to convert fish waste into protein the animals can eat.
- Biofouling (marine growth, fouling)
- The build-up of algae, barnacles, mussels and other organisms on submerged surfaces, which adds drag and weight and can block intakes and sensors.
- Biosecurity (biosecurity measures)
- Measures that keep diseases and pests out of a farm and stop them spreading within or beyond it.
- Blade rate (blade passing frequency, blade rate frequency)
- The frequency at which propeller blades pass a fixed point, shaft speed times blade count. It shows up as a modulation in radiated noise.
- Blue carbon
- Carbon captured and stored by coastal and marine ecosystems such as mangroves, seagrass meadows and salt marshes.
- Blue economy (ocean economy, blue bonds, blue bond)
- Economic activity based on the oceans, such as shipping, fishing, aquaculture, energy and tourism, ideally managed sustainably.
- Bose-Einstein condensate (BEC)
- A state of matter in which atoms cooled to near absolute zero share one quantum state, used in some advanced atom interferometers.
- Breathing gas mixtures (heliox, trimix, hydreliox, mixed gas diving)
- Diving gases that replace some or all nitrogen: heliox is helium and oxygen, trimix adds nitrogen, and hydreliox adds hydrogen for extreme depths.
C
- Cable plough (plough, cable plow, subsea plough)
- A towed seabed sled that cuts a trench, lays cable into it and covers it in one pass, burying it away from anchors and trawls.
- Cable protection zone (cable protection zones, protection zone)
- A sea area where anchoring, trawling or other seabed activities are restricted to protect submarine cables.
- Cable ship (cable repair ship, cable-laying ship, cable layer, cable vessel)
- A vessel built to lay, recover and repair submarine cables, with cable tanks, bow sheaves, cable engines and a jointing room for splicing.
- Capacity factorIn Batteries
- A plant's actual output over a period divided by what it would produce running at full power the whole time. Solar typically reaches ≈10–25%; storage owners use it to describe utilization.
- Carrier-phase positioning (carrier phase, carrier-phase differential GPS, CDGPS, RTK, real-time kinematic, ambiguity resolution)
- High-precision positioning that measures the phase of the radio carrier wave, not just its code. Resolving whole-cycle ambiguity gives centimeter accuracy.
- Cathodic protection (sacrificial anode, impressed current cathodic protection, ICCP)
- Slowing corrosion of submerged steel by making it the cathode of an electrical circuit, using sacrificial zinc or aluminum anodes or an impressed current.
- Cavitation (propeller cavitation, cavitation noise)
- The formation and collapse of vapor bubbles where water pressure drops, as on fast-turning propeller blades. It is the main source of a ship's broadband noise and can erode metal.
- Chokepoint (maritime chokepoint, choke point)
- A narrow sea passage, such as a strait or canal, through which much shipping must pass, so closure or attack can disrupt trade.
- Cold atoms (laser-cooled atoms, ultracold atoms, magneto-optical trap, MOT)
- Atoms cooled by lasers to millionths of a degree above absolute zero, where their quantum behavior can be used for precise sensing and timing.
- Commercial solutions openingIn Aerospace
- A US defense solicitation that invites companies to propose commercial technologies against broad problem statements, often leading to other transaction agreements.
- Container terminal (container port)In Industry
- The part of a port where container ships are loaded and unloaded and boxes are stored and moved to trucks and trains.
- Controlled-environment agriculture (CEA, vertical farming, vertical farm, indoor farming)
- Growing crops in enclosed, climate-controlled structures such as greenhouses and vertical farms, with controlled light, temperature, humidity and nutrients.
- Convergence zone (convergence zones)
- A ring at ≈50–60 km intervals where deep-refracted sound returns to the surface, allowing detection at long range in deep water.
- Coordinated Universal Time (UTC)
- The world's reference time scale, kept by atomic clocks and adjusted with leap seconds. Networks, power grids and finance synchronize to it.
- Critical undersea infrastructure (undersea infrastructure, subsea infrastructure)
- Subsea cables, pipelines and power links whose damage would disrupt communications, energy or economies, increasingly treated as a security target.
- Cycle life (cycle count)In Batteries
- The number of full charge-discharge cycles a battery delivers before its capacity falls to a set threshold, commonly 80% of the original. Test conditions such as depth of discharge and temperature change the result.
D
- DARPA (Defense Advanced Research Projects Agency)In Aerospace
- The US Defense Department agency that funds high-risk, high-payoff research, often through short, focused programs with industry and universities.
- Dead reckoning (DR navigation)
- Estimating position from a last known fix plus measured speed, heading and time.
- Deadweight tonnage (deadweight, DWT, dwt)
- The total weight a ship can safely carry, including cargo, fuel, water, stores and crew, in tonnes. It measures carrying capacity, not the ship's own weight.
- Deep Seabed Hard Mineral Resources Act (DSHMRA, commercial recovery permit, NOAA exploration licence, NOAA exploration license)In Minerals
- A 1980 US law under which NOAA licenses US citizens to explore and mine the deep seabed beyond national jurisdiction. A January 2026 NOAA rule allows one combined application for both.
- Defense Innovation Unit (DIU)In Aerospace
- A US Defense Department organization that helps the military adopt commercial technology quickly, often through other transaction agreements.
- DEMON analysis (DEMON)
- Detection of envelope modulation on noise, a technique that extracts propeller blade rate from broadband noise to estimate shaft speed and blade count.
- Desalination (reverse osmosis, RO, seawater desalination, solar still, solar desalination)
- Removing salt from seawater or brackish water to make fresh water, mainly by reverse osmosis or thermal distillation. Reverse osmosis uses ≈3–4 kWh per cubic metre of seawater.
- Dilution of precision (DOP, GDOP, HDOP, PDOP)
- A factor showing how the geometry of satellites or transmitters magnifies ranging errors into position error. Lower is better.
- Dissolved oxygen (DO level, dissolved oxygen level)
- The oxygen dissolved in water that fish and other aquatic life breathe, measured in mg/L. Low levels stress or kill stock.
- Distributed acoustic sensing (DAS, fiber-optic sensing)
- Using a fiber-optic cable as a long chain of vibration sensors by sending laser pulses down it and measuring scattered light.
- Distributed maritime operations (DMO)
- A US Navy concept that spreads forces across many dispersed crewed and uncrewed platforms to complicate enemy targeting.
- Diving support vessel (DSV, dive support vessel)
- A ship equipped with saturation diving systems, cranes and dynamic positioning to support divers and subsea work offshore.
- DoD Directive 3000.09 (Directive 3000.09)In Aerospace
- The US Defense Department policy on autonomy in weapon systems, last updated in 2023. It requires designs that allow appropriate levels of human judgment over the use of force and sets senior review before development and fielding.
- Doppler shift (Doppler)In Aerospace
- The change in a signal's frequency when transmitter and receiver move relative to each other. Fast low-orbit satellites cause large shifts that receivers must correct.
- Doppler velocity log (DVL)
- A sonar that measures a vessel's speed over the seabed or through the water from the Doppler shift of acoustic echoes, slowing inertial drift underwater.
- Dry deck shelter (DDS)
- A chamber mounted on a submarine's hull from which divers or vehicles can be launched and recovered while submerged.
- Dynamic positioning (DP)In Computing
- A computer-controlled system that holds a ship in place using its thrusters, essential during cable repair and offshore work.
E
- eLoran (enhanced Loran, Loran-C, Loran, LORAN)
- Enhanced Loran, a modernized low-frequency (90–110 kHz) terrestrial radio navigation and timing system. Its strong ground-based signals are hard to jam, making it a backup for satellite navigation.
- Emission control (EMCON)
- Deliberately limiting radio, radar and other emissions so a ship, submarine or vehicle is harder to detect.
- Eutrophication (dead zone, dead zones, hypoxic zone, algal bloom, harmful algal bloom)
- Excess nutrients, often from farm runoff or fish waste, that feed algal blooms which then decay and strip oxygen from the water, creating dead zones.
- Exclusive economic zone (EEZ, EEZs)In Minerals
- The sea out to 200 nautical miles from a country's coast, where it holds rights over fishing, energy and seabed minerals.
- Extractive species (extractive aquaculture, bivalves, filter feeders)
- Farmed organisms, such as seaweed, mussels and oysters, that need no feed because they take nutrients or food particles from the water.
F
- FDA approval pathways (IND, Investigational New Drug, NDA, New Drug Application, PMA, premarket approval)
- US routes to market for medical products. An IND lets a drug be tested in people and an NDA seeks its approval. Premarket approval is the strictest route for high-risk devices.
- Feed conversion ratio (FCR)
- The kilograms of feed needed to add one kilogram of animal weight. Lower ratios mean more efficient farming; farmed salmon is typically ≈1.1–1.3.
- Fishmeal (fish meal)
- Dried, ground fish used as a high-protein ingredient in aquaculture and livestock feed, made mostly from small wild-caught fish.
- Fixed seabed arrays (SOSUS, Sound Surveillance System, seabed sensor network)
- Networks of hydrophones laid on the seafloor to monitor ship and submarine traffic, such as the US Cold War SOSUS system.
- Floating farm (floating greenhouse, floating agriculture, farmship, maritime agriculture)
- A farm built on a floating platform or converted ship, growing crops, fish or livestock at sea or in harbors to free land and fresh water.
- Flow-through system (flow-through aquaculture)
- A fish farm that continuously draws in fresh water and discharges it after one pass.
- Free cooling (seawater cooling)In Computing
- Cooling a data center with cold outside air or water instead of mechanical chillers, saving energy.
G
- G-induced loss of consciousness (G-LOC, GLOC, +Gz)
- Blackout caused by sustained head-to-foot acceleration that drains blood from the brain, a hazard for fighter pilots.
- Galvanic corrosion (bimetallic corrosion)
- Accelerated corrosion that occurs when two different metals touch in seawater, which acts as an electrolyte.
- GNSS (global navigation satellite system, satellite navigation)In Aerospace
- The general term for satellite navigation systems, including GPS, Galileo, GLONASS and BeiDou. Receivers compute position from the timing of signals from several satellites.
- Grapnel (grapnels, grappling hook)
- A hooked tool dragged along the seabed from a cable ship to catch and lift a submarine cable for repair.
- Gravimeter (gravity gradiometer, quantum gravimeter)
- An instrument that measures local gravitational acceleration. Mobile gravimeters enable gravity-map navigation and subsurface surveys.
- Gross tonnage (GT)
- A measure of a ship's total enclosed internal volume, used to set port dues, crewing rules and safety requirements. Despite the name, it is not a weight.
- Groundwave (ground wave)
- A radio signal that travels along the Earth's surface rather than in a straight line, letting low-frequency signals such as eLoran reach far beyond the horizon.
- Gyroscope types (ring laser gyroscope, RLG, fiber-optic gyroscope, FOG, Sagnac effect)
- Rotation sensors used in navigation: ring laser and fiber-optic gyroscopes use light and the Sagnac effect; cold-atom gyroscopes use atom interferometry.
- Gyrostabilizer (gyroscopic stabilizer, gyro stabilizer)
- A spinning flywheel mounted in a vessel to resist rolling in waves.
H
- Head-on gutted (HOG, HOG weight)
- A trade form of fish with the guts removed but the head left on, the standard weight basis for salmon production and prices.
- High-pressure nervous syndrome (HPNS)
- Tremors, dizziness, nausea and impaired thinking caused by pressure itself on the nervous system, appearing in deep helium dives below ≈150 msw.
- Hotel load (hotel loads, house load)
- Electricity a vessel uses for everything other than propulsion, such as lighting, climate control, galley, navigation and computing.
- Hydrokinetic turbine (tidal stream turbine, hydrokinetic generator, marine current turbine)
- A turbine that generates electricity from moving water, such as tidal or river currents, without a dam.
- Hydrophone (hydrophones, hydrophone array)
- An underwater microphone that converts sound pressure into an electrical signal. Arrays of hydrophones can tell the direction of a sound.
- Hydroponics (nutrient film technique, NFT, deep-water culture, DWC, aeroponics)
- Growing plants without soil, with roots in a nutrient solution. Nutrient film technique and deep-water culture are common methods; aeroponics mists the roots instead.
- Hyperbaric chamber (decompression chamber, recompression chamber, hyperbaric oxygen therapy)
- A sealed chamber pressurized above atmospheric pressure, used for saturation diving, decompression and medical treatment.
I
- ILA-USMX master contract (ILA, USMX, International Longshoremen's Association, United States Maritime Alliance)In Industry
- The labor agreement between US East and Gulf Coast dockworkers and port employers, running to 30 September 2030. It bars fully automated terminals and equipment and requires agreement before semi-automation is introduced.
- Inert gas narcosis (nitrogen narcosis, narcosis)
- An intoxication-like impairment caused by breathing nitrogen or other inert gases at high pressure, which limits air diving depth.
- Inertial drift (bias drift, bias stability, scale-factor error, sensor drift)
- The growing position error of an inertial system as small sensor errors, such as bias and scale-factor errors, accumulate over time.
- Inertial measurement unit (IMU)In Aerospace
- A sensor package of accelerometers and gyroscopes that measures a vehicle's acceleration and rotation. It is the core of autopilots and of navigation without satellite positioning.
- Innocent passage (right of innocent passage)
- The right under the Law of the Sea for foreign ships to pass through a country's territorial sea, provided they do not threaten its peace or security.
- Integrated multi-trophic aquaculture (IMTA, polyculture)
- Farming fed species, such as fish, alongside extractive species, such as seaweed and shellfish, that take up their waste nutrients.
- Intelligence, surveillance and reconnaissance (ISR)In Aerospace
- Collecting and processing information about an adversary or area with sensors on aircraft, satellites and other platforms. Many drones and high-altitude platforms are bought mainly for it.
- International Cable Protection Committee (ICPC)
- An industry body of cable owners, operators and governments that sets recommendations for protecting and repairing submarine cables.
- International Maritime Organization (IMO)
- The UN agency in London that sets global rules for shipping safety, security and pollution, such as SOLAS and MARPOL.
- InverterIn Batteries
- A power electronic device that converts direct current (DC) from batteries or solar panels into alternating current (AC). Inverter losses and size are part of every storage system's cost.
J
- Jamming and spoofing (jamming, spoofing, anti-jam, anti-spoofing)In Aerospace
- Jamming drowns out a signal with noise; spoofing feeds a receiver false signals, such as fake satellite navigation data, so it computes the wrong position. Both are routine against drones.
- JANUS (STANAG 4748, JANUS protocol)
- The NATO standard (STANAG 4748), promulgated in 2017, for digital underwater acoustic messaging, giving equipment from different makers a common first contact signal.
K
- KnotIn Aerospace
- A speed of one nautical mile per hour, ≈1.852 km/h. Aviation and shipping use it worldwide.
L
- Levelized cost of electricity (LCOE)In Industry
- The lifetime cost of building and running a power plant divided by the electricity it produces, in $/MWh, used to compare technologies.
- Liquid breathing (liquid ventilation, perflubron, partial liquid ventilation, total liquid ventilation, perfluorocarbon liquid ventilation)
- Breathing an oxygen-rich perfluorocarbon liquid instead of gas. Partial liquid ventilation adds liquid to the lungs alongside gas; total liquid ventilation replaces gas entirely.
- LOFAR analysis (LOFAR, LOFARgram)
- Low-frequency analysis and recording, a spectral display that reveals the steady tonal lines from a vessel's machinery, used to classify it.
- Loitering munition (one-way attack drone, kamikaze drone)In Aerospace
- A weapon that flies to an area, circles while searching for a target, then dives into it. It blends a drone with a missile and is usually expendable.
M
- Marine energy (ocean energy, marine renewable energy)
- Power from waves, tides, currents and ocean temperature or salinity differences.
- Marine spatial planning (MSP, ocean zoning, ecosystem-based management)
- A public process for deciding which human activities take place where at sea, balancing uses such as shipping, energy, fishing and conservation.
- Metres of seawater (msw, feet of seawater, fsw)
- A unit of pressure expressed as depth in seawater; every ≈10 msw adds about one atmosphere of pressure.
- MicrogridIn Batteries
- A local grid with its own generation and storage that can run connected to the main grid or alone, in island mode. Ports, campuses and remote sites use microgrids for resilience.
- Microreactor (micro-reactor, nuclear microreactor)In Industry
- A very small nuclear reactor, typically up to ≈20 MWe, that can be transported by truck or ship to power remote sites or military bases for years without refueling.
- Multibeam echo sounder (MBES, multibeam sonar)
- A sonar that sends a fan of beams to map a wide swath of seafloor depth in one pass.
- Multipath (multipath propagation)
- A signal arriving at a receiver by several paths, such as direct and reflected, at slightly different times. It distorts underwater acoustic links and degrades radio positioning.
N
- Nautical mile (nmi)In Aerospace
- A distance of 1,852 m by international definition, used in aviation and shipping because it relates to minutes of latitude.
- Net pen (open-net pen, sea cage, net cage)
- A floating cage in a lake or sea where fish are raised, with waste and escapes flowing into surrounding waters.
- Nodule collector (collector vehicle, collector, riser, riser system, lift system)In Minerals
- A seabed vehicle that picks up nodules and pumps them through a riser pipe to a surface ship. The riser and flexible hoses link the two.
- Nuclear-powered submarines (SSN, SSBN, attack submarine, ballistic missile submarine)
- Submarines driven by onboard reactors that can stay submerged for months. Attack submarines (SSN) hunt ships and submarines; ballistic missile submarines (SSBN) carry nuclear deterrent missiles.
O
- Ocean acidification
- The fall in seawater pH as the ocean absorbs carbon dioxide from the air, which makes it harder for shellfish and corals to build shells and skeletons.
- Ocean data center (underwater data center, subsea data center, floating data center)
- A data center sited at sea or on the seabed, using seawater for cooling and sometimes ocean energy for power.
- Ocean thermal energy conversion (OTEC)
- Generating power, and often fresh water, from the temperature difference between warm tropical surface water and cold deep water.
P
- Peak shaving (peak-shaving, demand charge management)In Batteries
- Using stored energy to cut the highest points of a site's or grid's demand, which lowers demand charges and delays grid upgrades.
- Perfluorocarbons (PFCs, PFC, CF₄, C₂F₆)In Industry
- Very long-lived, potent greenhouse gases, mainly CF₄ and C₂F₆, released by aluminum smelters during anode effects. Each tonne warms thousands of times more than a tonne of CO₂.
- Periscope depth
- The shallow depth at which a submarine can raise its periscope or masts to communicate or take a satellite fix, at higher risk of detection.
- Piezoelectric transducer (PZT, acoustic transducer)
- A ceramic element that turns electrical signals into sound and sound into electrical signals, the core of most sonar and acoustic modems.
- PNT (positioning, navigation and timing, positioning, navigation, and timing, resilient PNT, complementary PNT)
- Positioning, navigation and timing, the services that tell users where they are and what time it is. Most depend on satellite signals, so backups are a security priority.
- Polymetallic nodules (manganese nodules, nodules, polymetallic nodule)In Minerals
- Potato-sized lumps on the abyssal seafloor rich in manganese, nickel, copper and cobalt, formed over millions of years. The Clarion-Clipperton Zone holds the largest fields.
- Port automation (automated terminal, semi-automated terminal)In Industry
- Running terminal equipment such as stacking cranes, vehicles and gates with software and remote or autonomous control. It raises consistency and safety but faces labor agreements and high upfront costs.
- Power take-off (PTO)
- The mechanism in a wave or tidal device, such as a hydraulic system, linear generator or turbine, that converts motion into electricity.
- Power usage effectiveness (PUE)In Computing
- Total data center power divided by the power used by the computing equipment. A value of 1.0 would be perfect; efficient modern sites reach ≈1.1–1.2.
- Pressure-tolerant design (pressure-compensated, pressure-tolerant)
- Building subsea equipment, such as batteries, to work flooded or oil-filled at ambient sea pressure instead of inside heavy pressure housings.
- Program of recordIn Aerospace
- A defense program with its own line in the budget and an approved acquisition plan, giving it multi-year funding. Becoming one is a key milestone for a defense startup's product.
- PseudoliteIn Aerospace
- A ground- or air-based transmitter that broadcasts signals like those of navigation satellites, to add to or replace satellite positioning in a local area.
- Pseudorange (pseudoranges)
- The apparent distance to a navigation transmitter, from signal travel time, before receiver clock error is removed.
Q
- Quantization (int8 quantization, product quantization)In Computing
- Storing a model's numbers at lower precision, such as 8-bit integers instead of 32-bit floats, to cut memory and speed up computation at a small accuracy cost.
- Quantum inertial sensors (quantum navigation, quantum inertial navigation, quantum gyroscope, quantum accelerometer)
- Accelerometers, gyroscopes and gravimeters based on cold-atom interferometry, aimed at navigating for long periods without satellite fixes.
R
- ReachstackerIn Industry
- A heavy vehicle with a telescopic boom that lifts and stacks containers, used where cranes are not available.
- Recirculating aquaculture system (RAS, recirculating aquaculture)
- A land-based fish farm that filters and reuses most of its water, controlling temperature, oxygen and waste, at the cost of high energy use and capital.
- Reefer container (reefer, reefers, refrigerated container)
- A refrigerated shipping container that needs electrical power aboard ship and at the terminal to keep cargo cold.
- Remotely operated vehicle (ROV, work-class ROV)In Computing
- An uncrewed underwater robot controlled from a ship through a tether, used for cable repair, inspection and seabed work.
- Replicator (Replicator initiative)In Aerospace
- A US Defense Department initiative announced in 2023 to field thousands of cheap, attritable autonomous systems within about two years. In November 2025 its portfolio moved to the Defense Autonomous Warfare Group.
- Route survey (cable route survey, marine route survey)
- A pre-installation survey of the seabed corridor a cable or pipeline will follow, using bathymetry, sub-bottom profiling and sampling.
S
- Saturation diving (saturation diver, sat diving)
- A deep-diving method in which divers live under pressure in a chamber for days or weeks. Their tissues become saturated with gas, so they decompress only once, at the end.
- Sea state (Douglas sea scale)
- A scale describing wave and swell conditions, from calm to phenomenal. It limits when vessels, vehicles and divers can be launched and recovered.
- Seabed warfare (seabed operations)
- Military operations on or near the seafloor, including attacking or protecting cables, pipelines and sensors.
- Seaweed farming (kelp farming, seaweed cultivation, kelp, macroalgae)
- Growing kelp and other seaweeds on ropes or nets in the sea for food, feed, fertilizer and materials. It needs no freshwater, feed or fertilizer.
- Sediment plume (plume, discharge plume, midwater plume, turbidity current)In Minerals
- A cloud of fine sediment stirred up by seabed mining or discharged from the ship, which can drift far and smother seafloor life.
- Semi-fuel cell (metal-water semi-fuel cell, aluminum-seawater battery)
- An underwater power source in which a metal such as aluminum reacts with seawater to make electricity, giving long endurance without carrying an oxidizer.
- Ship stability (stability margin, metacentric height, intact stability)
- A ship's ability to return upright after heeling, set by where its center of gravity sits relative to its buoyancy. Heavy loads carried high, such as deck batteries, reduce the margin.
- Ship-to-shore crane (STS crane, STS, quay crane)In Industry
- The large quay crane that lifts containers between ships and the terminal. Its moves per hour set how fast a ship is turned around.
- Shore power (cold ironing, onshore power supply)In Batteries
- Supplying electricity from land to a docked ship so it can switch off its engines. It cuts port emissions but needs large grid connections at the berth.
- Significant wave height (Hs, SWH)
- The average height of the highest third of waves in a sea state, the standard measure of wave conditions for design and operations.
- Small modular reactor (SMR, SMRs, small modular reactors)In Industry
- A nuclear fission reactor of up to ≈300 MWe, designed to be built largely in factories and installed in modules. Smaller size aims to cut cost and construction risk.
- Sodium-ion battery (Na-ion, SIB, sodium-ion)In Batteries
- A rechargeable battery that uses sodium ions instead of lithium. Sodium is abundant and cheap, and cells work well in the cold, but energy density is lower than LFP.
- Sonar (passive sonar, active sonar, SONAR)
- Sound navigation and ranging, the use of underwater sound to detect, locate and identify objects. Passive sonar only listens; active sonar sends pings and listens for echoes.
- Sonobuoy (sonobuoys)
- An expendable buoy dropped from aircraft or ships that listens with a hydrophone and radios the sounds back for anti-submarine search.
- Sound speed profile (SSP, sound velocity profile, sound-speed gradient)
- How the speed of sound in seawater changes with depth, set by temperature, pressure and salinity. It bends sound paths and creates shadow zones and long-range channels.
- Spectrogram (STFT, short-time Fourier transform, mel spectrogram)
- An image of how a signal's frequency content changes over time, usually made with a short-time Fourier transform. It is the standard input for acoustic classifiers.
- Spinning reserve (contingency reserve, operating reserve)In Batteries
- Generating or storage capacity that is online and ready to supply power within minutes if a plant or line fails.
- Splash zone
- The part of an offshore structure repeatedly wetted by waves and spray, usually the most corrosive area.
- State of charge (SOC, SoC)In Batteries
- How full a battery is, as a percentage of its usable capacity. Battery management systems estimate it continuously; operators often avoid keeping cells near 0% or 100% to slow wear.
- Station-keepingIn Aerospace
- Small, regular corrections that hold a satellite or high-altitude platform at its assigned position. On geostationary satellites the propellant for station-keeping often sets working life.
- Stocking density (stocking rate)
- The weight or number of animals per unit of water volume, which affects growth, welfare and disease risk.
- Stowage plan (stowage, bay plan)
- The planned position of every container or cargo item aboard a ship, balancing weight, stability, port order and hazards.
- Straddle carrier (automated straddle carrier)In Industry
- A tall vehicle that straddles a container, lifts it and carries it around a terminal. Automated versions run without drivers.
- Sub-bottom profiler (sub-bottom profiling, SBP)
- A low-frequency sonar that images sediment layers beneath the seafloor, used in cable and pipeline route surveys.
- Submarine cable (undersea cable, subsea cable, submarine fiber)In Computing
- A fiber-optic cable laid on the seabed to carry internet traffic between continents. Repeaters along the route boost the signal; landing stations connect it to land networks.
- Submarine cable components (repeater, branching unit, cable landing station, SLTE, submarine line terminal equipment, wet plant, dry plant)In Computing
- The main parts of an undersea cable system. Wet plant is everything in the sea, such as repeaters and branching units; dry plant is the shore equipment, including the submarine line terminal equipment (SLTE).
- Subsea power cable (export cable, subsea export cable, interconnector)
- A high-voltage cable on the seabed that carries electricity from offshore generation to shore or between grids.
- Superstructure (deckhouse, accommodation block)
- The structures built above a ship's main deck, such as the deckhouse and bridge, holding accommodation, controls and machinery.
- Syntactic foam
- A buoyant composite of hollow glass microspheres in resin that resists crushing at depth, used for flotation on deep vehicles.
T
- Terminal tractor (yard truck, yard tractor, port tractor, terminal truck)In Industry
- A short truck that tows container chassis between quay, yard and gates. It is a leading target for battery power and autonomy.
- TEU (twenty-foot equivalent unit, FEU)In Industry
- Twenty-foot equivalent unit, the standard measure of container volume. A 40-foot container counts as 2 TEU; ship and port capacity are quoted in TEU.
- The Area (international seabed area, areas beyond national jurisdiction)In Minerals
- Under the Law of the Sea, the seabed beyond any country's national jurisdiction, whose minerals are managed by the International Seabed Authority.
- Time difference of arrival (TDOA)
- Locating a receiver or transmitter from differences in signal arrival times between stations or sensors.
- Towed array (towed array sonar, towed line array)
- A long line of hydrophones towed far behind a ship or submarine, away from its own noise, to detect quiet low-frequency sounds.
- Transformer (transformer model, attention mechanism)In Computing
- The neural network design behind most large language models, built around an attention mechanism that relates every token to every other. Its compute cost grows with the square of input length.
U
- Ultra-large container vessel (ULCV, ULCS, ultra-large container ship, megaship)
- The largest class of container ship, roughly 400 m long and able to carry ≈20,000–24,000 TEU. Only deep, well-equipped hub ports can handle them.
- UNCLOS (United Nations Convention on the Law of the Sea, Law of the Sea, Part XI, 1994 Implementation Agreement)In Minerals
- The 1982 UN Convention on the Law of the Sea. Its Part XI, as changed by a 1994 agreement, governs mining in the Area. The US has not ratified it.
- Uncrewed undersea vehicle (UUV, UUVs, unmanned undersea vehicle, unmanned underwater vehicle)
- Any underwater vehicle without people aboard, either remotely controlled through a tether or operating autonomously.
- Underwater acoustic communication (acoustic modem, acoustic link, underwater acoustic modem)
- Sending data through water by sound, the only practical long-range underwater channel, at low data rates because of limited bandwidth and multipath.
- Underwater acoustic datasets (ShipsEar, DeepShip)
- Public recordings used to train and benchmark ship-noise classifiers, such as ShipsEar from the Spanish coast and DeepShip, with ≈47 hours from 265 ships.
- Underwater acoustic target recognition (UATR, acoustic target classification)
- Classifying ships, submarines and marine life from the sounds they radiate, increasingly with machine learning on spectrograms.
- Underwater optical communication (blue-green laser communication, optical modem)
- Short-range, high-rate data links through water using blue-green light, which seawater absorbs less than other wavelengths.
- Underwater radiated noise (URN, ship noise, underwater noise)
- Sound that ships emit into the sea, mostly from propeller cavitation and machinery, which can disturb marine life. The IMO's guidelines to reduce it, revised in 2023, are voluntary.
- Underway replenishment (replenishment at sea, UNREP)
- Transferring fuel, stores or munitions between ships while both are moving, which lets a fleet stay at sea for long periods.
- UUV size classes (XLUUV, extra-large UUV, XL-AUV, LDUUV, large-displacement UUV, heavyweight UUV)
- US Navy classes of uncrewed undersea vehicles by diameter and weight: man-portable, lightweight, heavyweight, large-displacement and extra-large. Extra-large vehicles, over ≈10 m, launch from piers rather than submarines.
V
- Value stackingIn Batteries
- Earning several revenue streams from one storage asset, such as arbitrage, reserves and backup power, to make it pay.
W
- Wave energy converter (WEC, wave energy device, wave converter, wave power)
- A device that turns the motion of ocean waves into electricity, such as point absorbers, attenuators and oscillating water columns.
- Weather window (sea-state window, operational window)
- A period of sea and weather conditions calm enough for a marine operation, such as cable repair, installation or diving.
Y
- Yard cranes (rubber-tyred gantry crane, RTG, rail-mounted gantry crane, RMG, automated stacking crane, ASC)In Industry
- Gantry cranes that stack and retrieve containers in a terminal's storage yard. Rubber-tyred versions move freely; rail-mounted and automated stacking cranes run on fixed tracks.