Index of underwater diving: N–Z

The following index is provided as an overview of and topical guide to underwater diving: Links to articles and redirects to sections of articles which provide information on each topic are listed with a short description of the topic. When there is more than one article with information on a topic, the most relevant is usually listed, and it may be cross-linked to further information from the linked page or section.

Underwater diving can be described as all of the following:

A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.

N

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Subsection: Top, Na, Ne, Ni, No, Nu

Na

Namibian Marine Corps – Combat body created in 2016
National Academy of Scuba Educators (NASE) – Recreational scuba training and certification agency
National Association for Cave Diving (NACD) – American non-profit organization for improving cave diving safety
National Association of Underwater Instructors (NAUI) – Non-profit training and certification agency association of scuba instructors
National Board of Diving and Hyperbaric Medical Technology – Non-profit organization for education and certification in diving and hyperbaric medicine
National Diving and Activity Centre – Flooded quarry in Gloucestershire used as a recreational dive site.
National Navy UDT-SEAL Museum – Museum of US Navy special forces units
National Oceanic and Atmospheric Administration (NOAA) – US government scientific agency
National Speleological Society Cave diving section – Organization for exploration, conservation, and study of caves in the United States
NATO Submarine Rescue System – Project to develop an international submarine rescue system
Nautical Archaeology Program – Graduate degree program at Texas A&M University
Nautical Archaeology Society (NAS) – British organisation to further research in nautical archaeology for the public benefit
Nautile – Crewed submersible owned by Ifremer
Naval Air Command Sub Aqua Club – British organization within the Royal Navy
Naval diving – Diving in navy applications
Naval Diving Unit (Singapore) – Maritime special forces unit
Naval Service Diving Section – Diving unit of the Irish Naval Service
Naval Special Operations Command – Military unit of the Philippines Navy
Naval Special Warfare Command (Thailand) – Special operations force within the Military of Thailand
Naval Submarine Medical Research Laboratory – U.S. Navy research unit for submarine and diving medicine
Navy diver (disambiguation) – Member of a country's naval forces, specializing in underwater diving
Navy diver (United States Navy) – US Navy personnel qualified in underwater diving and salvage

Ne

Neck dam – Flexible seal between a diving helmet and the diver's neck
Necker Nymph – DeepFlight Merlin class positively-buoyant open-cockpit 3-seater wet sub
Nederlandse Onderwatersport Bond (NOB) – Dutch governing body for underwater sports
Negative buoyancy entry – Scuba diving water entry where the diver will immediately sink
Negative pressure breathing – Breathing gas which is at a slightly lower pressure than in the resting lung
Nemo 33 – Indoor recreational diving facility
Nemrod – Spanish manufacturer of scuba and spearfishing equipment
Neptune Finswimming Club – Club in Bristol, UK.
Nereus (underwater vehicle) – Hybrid remotely operated or autonomous underwater vehicle
Neutral buoyancy – Equilibrium between buoyancy and weight of an immersed object
Neutral Buoyancy Laboratory – NASA astronaut training facility in Houston, Texas
Neutral buoyancy pool – Pool of water in which neutral buoyancy is used to train astronauts
Newtsuit – Atmospheric diving suit designed by Phil Nuytten
New World Publications – Recreational dive guide publisher

Ni

Night diver – Certification of competence to scuba dive at night
Night diving – Underwater diving during the hours of darkness
Nikonos – Brand of 35mm film amphibious cameras
Nitrogen narcosis – Reversible narcotic effects of respiratory nitrogen at elevated partial pressures
Nitrous oxide (medication) – Gas used as anesthetic and for pain relief
Nitrox – Breathing gas, mixture of nitrogen and oxygen
Nitrox blender – Person competent to blend nitrox for scuba diving
Nitrox diver – Recreational diving qualification to dive using oxygen enriched air
Nitrox production – Methods of producing nitrox mixtures

No

NOAA Diving Manual – Training and operations manual for scientific diving
No-decompression limit (NDL) – Maximum exposure without incurring decompression obligation
NOGI Awards – Annual awards by Academy of Underwater Arts and Sciences.
No-limits apnea – Freediving discipline in which the diver descends and ascends using their method of choice
Nondestructive testing – Evaluating the properties of a material, component, or system without causing damage
Non-freezing cold injury – Tissue injury due to sustained low temperature without freezing
Nordic Deep – Freediving competition in Lysekil, Sweden
Normocapnia – Normal arterial carbon dioxide levels
Normoxic breathing gas – Mixture with similar oxygen content to air
Normoxic trimix – Breathing gas mixture of helium, nitrogen, and at least 18% oxygen
Normoxic trimix diver – Recreational technical diving certification level
Northern Ireland Federation of Sub-Aqua Clubs – National governing body for recreational diving and underwater sport in Northern Ireland
Norwegian Diver School – Part of the Western Norway University of Applied Sciences
No-stop limit – Diving bottom time beyond which obligatory decompression stops are incurred

Nu

Nuclear diving – Diving in an environment where there is a risk of exposure to radioactive materials

O

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Subsection: Top, Ob, Oc, Of, Om–On, Op, Or, Os, Ou, Ov, Ox

Ob

Observation bell – Closed diving bell used as an observation platform

Oc

Occupational diver – Person who dives underwater as part of their occupation
Occupational diver training – Training of people employed as underwater divers
Occupational diving – Underwater diving which is part of the job
Occupational exposure limit – Upper limit on the acceptable concentration of a hazardous substance
Occupational hazard – Hazard experienced in the workplace
Occupational Health and Safety Act, 1993 – South African statutory law administered by the Department of Labour
Occupational hygiene – Management of workplace health hazards
Occupational safety and health, also known as Occupational health and safety – Field concerned with the safety, health and welfare of people at work
Ocean current – Directional mass flow of oceanic water generated by external or internal forces
Ocean Guardian – Personal electromagnetic field shark deterrent device
Ocean stratification – Layering of ocean water due to density differences
Oceanic Worldwide – American recreational scuba equipment manufacturer
Octopus demand valve, also known as octopus regulator – Secondary demand valve on a scuba regulator

Of

Off-board gas – Feed gas for a rebreather supplied from an external cylinder
Offshore commercial diving – Professional diving in support of the oil and gas industry
Offshore construction – Installation of structures and facilities in a marine environment
Offshore diving – Diving outside the territorial waters of a country
Offshore survey – Discipline of hydrographic survey largely concerned with the oil industry

Om–On

Omitted decompression – Missed obligatory decompression stops
Omitted decompression procedure – Procedure to reduce risk of developing decompression sickness
On-board gas – Gas supply carried as integral part of equipment

Op

Open bell – Platform for lowering and lifting divers with an open-bottomed air space
Open circuit breathing apparatus – Breathing apparatus where the exhaled gas is lost to the environment
Open circuit demand helmet – Diving helmet which provides gas on inhalation and exhausts to the surroundings
Open ocean diving – Diving in deep water out of sight of land
Open water (diving) – Unrestricted water with free vertical access to the surface
Open Water Diver – Entry-level autonomous diver certification for recreational scuba diving
Open-water diving – Diving in unrestricted water when the diver has unresricted vertical access to the surface
OpenROV – Open-source remotely operated underwater vehicle
Operation Algeciras – Argentine plan to sabotage a British warship in Gibraltar
Operation Source – Second World War Royal Navy midget submarine attacks on heavy German warships in Norway
Operation Thunderhead – American amphibious mission during the Vietnam War
Operational Diving Division (SA Navy) – Diving component of the South African Navy's Maritime Reaction Squadron
Operations manual – Authoritative document of how things should be done in an organisation

Or

Orca Edge – First commercially viable personal decompression computer
Orinasal mask, also known as Oral-nasal mask – Breathing mask that covers the mouth and the nose only.

Os

Osprey Reef – Submerged atoll in the Coral Sea, northeast of Queensland, Australia

Ou

Outline of recreational dive sites – Hierarchical outline list of articles about rereational dive sites
Outline of underwater divers – Hierarchical outline list of biographical articles about underwater divers
Outline of underwater diving – List of articles related to underwater diving grouped by topical relevance
Out-of-gas emergency, also known as Out-of-air emergency – Underwater diving incident involving loss of breathing gas supply
Out-of-gas incident, also known as out-of-air incident – Underwater diving incident involving loss of breathing gas supply

Ov

Overfall – Dangerously steep and breaking seas due to currents over shallow obstructions
Overconfidence effect – Personal cognitive bias
Overhead environment, also known as overhead (diving) – Environment with a physical constraint to a direct vertical ascent to the surface
Over-learning, also known as Overlearning – Practicing newly acquired skills beyond the point of initial mastery
Overpressure valve (rebreather loop) (OPV) – Pressure relief valve on a breathing loop

Ox

Oxygen analyser – Instrument to measure partial pressure of oxygen in a gas mixture
Oxugen cell – Electro-galvanic fuel cell used for measuring oxygen concentration
Oxygen cleaning – Removal of contaminants that might cause a fire hazard in an oxygen rich environment
Oxygen compatibility – Usability in high-oxygen environments
Oxygen decompression – Use of oxygen for accelerated decompression
Oxygen enriched air – Air with added oxygen
Oxygen fraction – The molar or volumetric fraction of oxygen in a gas
Oxygen prebreathing – Procedure to reduce risk of decompression sickness before hypobaric exposure
Oxygen service – Use in contact with high partial pressures of oxygen
Oxygen therapy – Use of oxygen as a medical treatment
Oxygen toxicity – Toxic effects of breathing oxygen at high partial pressures
Oxygen toxicity seizure – Underwater diving emergency
Oxygen window, also known as oxygen window in technical diving – Physiological effect of oxygen metabolism on the total dissolved gas concentration in venous blood

P

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Subsection: Top, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py

P2 – Svenskt Vrakskydd – Organization for presrvation of shipwrecks in Swedish waters

Pa

PADI Advanced Rebreather Diver – Minimum PADI certification meeting Rebreather Training Council standards
PADI AWARE – Marine conservation non-profit organization for recreational divers
PADI Delayed Surface Marker Buoy Diver – Diver trained to deploy a decompression buoy from depth
PADI Discover Scuba Diving – Introductory scuba experience without certification
PADI Low Impact Diver – Training to mitigate low entry level competence standards
PADI Open Water Diver – Entry level recreational diving certification
PADI Peak Performance Buoyancy – PADI diver with buoyancy control skill
Panic – Sudden overwhelming sensation of fear
Parachute lift bag – Open bottomed airtight bag used for underwater buoyant lifting when filled with air
Partial pressure – Pressure of a component gas in a mixture
Partial pressure blending – Gas blending based on pressure ratio of components
Partial pressure vacancy – Physiological effect of oxygen metabolism on the total dissolved gas concentration in venous blood
PASKAL – Special operations force of the Royal Malaysian Navy
Passive addition semi-closed circuit rebreather, also known as passive addition rebreather – Dumps gas from the breathing circuit and makes up volume on demand
Patent foramen ovale – A heart defect present at birth

Pe

Pearl hunting – Collecting pearls from wild molluscs
Pearling in Western Australia – Local aquaculture industry
Pelagic Pressure Systems – Manufacturer of dive computers
Pendulum rebreather – Configuration using biderctional gas flow
Pendulum search – Diver search pattern
Penetration dive – Dive under a physical barrier to a direct vertical ascent to the surface
Penetration diving – Diving under a physical barrier to a direct vertical ascent to the surface
Peress, Joseph Salim – Pioneering British diving engineer
Performance Freediving International (PI) – Freediver training agency
Perfusion – Passage of fluid through the circulatory or lymphatic system to an organ or tissue
Permanent set – Plastic deformation
Permeation – Penetration of a liquid, gas, or vapor through a solid
Permit-to-work – Work safety management system
Personal diving equipment – Underwater diving equipment worn by the diver
Personal protective equipment – Equipment designed to help protect an individual from hazards

Ph

Philippine Underwater Hockey Confederation – National sports association
Phoenix International Holdings – Marine services company for underwater operations
Physiological effects of the use of breathing apparatus
Physiological response to water immersion – Also known as the diving response and mammalian diving reflex
Physiology of decompression – The physiological basis for decompression theory and practice
Physiology of diving adaptations – Adaptations of marine vertebrates to diving
Physiology of human diving – Influences of the underwater environment on the physiology of human divers

Pi

Pillar valve – Type of scuba cylinder valve
Piccard, Auguste – Swiss physicist, inventor, and explorer
Pinch point hazard – Mechanical hazard which may damage or injure by reducing a gap
Pipeline end manifold (PLEM) – Termination of a rigid pipeline

Pn

Pneumofathometer – Instrument for measuring the depth of a diver by air pressure

Po

Polespear – Basic rubber launched underwater fishing spear
Police diving – A branch of professional diving carried out by police services
Neal W. Pollock – Canadian researcher in diving physiology and hyperbaric medicine
Pony bottle – Small independent scuba cylinder usually carried for emergency gas supply
Pool part of the 2011 Finswimming World Championships – International competition in Hódmezővásárhely, Hungary
Pool part of the 2013 Finswimming World Championships – International competition in Kazan, Russia
Porpoise (rebreather) – Australian oxygen rebreather
Porpoise (scuba gear) – Australian scuba manufacturer
Powerhead – Specialized firearm used underwater that is fired when in direct contact with the target
Positive pressure breathing – Breathing gas which is at a slightly higher pressure than in the resting lung
Positive pressure breathing apparatus – Equipment in which pressure insude the facepiece is always higher than ambient pressure
Positive pressure open circuit breathing apparatus – Apparatus supplying gas at a pressure slightly above ambient
Potable water diver – Person competent to dive in potable water systems
Potable water diving – Underwater diving in potable water systems
Power inflator – Low pressure gas supply valve for buoyancy compensator
PowerSwim – Diver-powered propulsion device

Pr

Pre-dive briefing – Meeting of the dive team to discuss details before the diving operation
Pre-dive checks – Checks done prior to entering the water for a dive
Preparing the diving rebreather – Assembly and predive function tests
Pressure – Force distributed over an area
Pressure reducing regulator – Pressure control valve that maintains the downstream pressure setting
Pressure reduction regulator – Control valve that reduces and maintains the outlet pressure of a fluid
Pressure swing adsorption – Method of gases separation using selective adsorption under pressure
Pressure-tight zipper – Zip fastener capable of a seal across a gas pressure difference
Pressure transmitter (diving) – Cylinder pressure transducer with wireless transmitter linked to dive computer
Pressure vessel for human occupancy, also known as pressure vessel for human occupation – Container to be occupied by one or more people with an internal pressure different from outside
Primary demand valve – The second stage regulator that the diver normally uses
Priz-class deep-submergence rescue vehicle – Russian submersibles
Professional Association of Diving Instructors (PADI) – Recreational diver training and certification agency
Professional Divers' Association of Australia – Trade union
Professional diver training – Training of candidates for registration as professional divers
Professional diving, also known as Occupational diving – Underwater diving where divers are paid for their work
Professional Diving Instructors Corporation (PDIC) – Recreational diver training and certification agency
Professional scuba diver – Person with skills and knowledge required for occupational scuba diving
Professional scuba diving – Occupational diving using scuba
Professional Technical and Recreational Diving – Diver certification agency
Protection of Military Remains Act 1986 – UK legislation protecting wreckage of military ships and aircraft
Protection of Wrecks Act 1973 – UK legislation on conservation of shipwrecks

Ps

Psychological fitness to dive – Psychological fitness of a person to function safely underwater under pressure
Psychosocial hazard – Occupational hazard to one's psychological well-being
Psychrometric constant – Relation of the partial pressure of water in air to temperature

Pu

Public safety diver – Diver working in the public safety sector
Public safety diver training – Training divers for public safety services
Public safety diving – Underwater work done by law enforcement, rescue and search and recovery teams
Pulmonary barotrauma – Lung over-pressure and squeeze injuries
Pulmonary circulation – Part of the circulatory system which carries blood from heart to lungs and back to the heart
Pulmonary edema of immersion – Body fluid in the lungs while immersed
Pulmonary oxygen toxicity – Lung injury due to nlong term exposure to high oxygen levels
Pulmonary volutrauma – Lung injury due to over-expansion
Purge button – Manual activation control of the demand valve

Py

Pyle stop – Type of short deep decompression stops in addition to the standard profile
Pyle, Richard – American ichthyologist and scuba diver

Q

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Quintana Roo Speleological Survey – Data repository for explored sites within the state of Quintana Roo

R

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Subsection: Top, Ra, Re, Ri–Rn, Ro, Ru

R-2 Mala-class swimmer delivery vehicle – 2-man wet sub swimmer delivery vehicle class of the Yugoslavian, and later, Croatian, Navies

Ra

Rack operator – Member of a surface-supplied diving team who operates the breathing gas panel
Raid on Alexandria (1941) – Italian frogman raid on British warships
Raid on Algiers – Italian frogman raid on Allied ships in Algiers harbour in 1942
Rash guard, also known as Rash vest – Stretch garment for protection from abrasion, UV and stings
Ratchet reel (diving) – Type of reel used by divers to deploy and recover line
Ratio deco – Rule of thumb for estimating a decompression schedule for a given set of breathing gases
Ratio decompression – Rule of thumb for estimating a decompression schedule for a given set of breathing gases
Rawlins, John – Royal Navy officer and pioneer in the field of diving medicine

Re

Rebreather – Portable apparatus to recycle breathing gas
Rebreather ascents and descents – Loop volume and partial pressure control with changes in ambient pressure
Rebreather Association of International Divers (RAID) – Recreational diver training and certification agency
Rebreather bailout – Switching over to an alternative supply of breathing gas
Rebreather diluent flush, also known as diluent flush, or dil flush – Replacing gas in the loop with fresh diluent
Rebreather diver – Scuba diving qualification to use a rebreather
Rebreather diving – Underwater diving using self contained breathing gas recycling apparatus
Rebreather Education and Safety Association (RESA) – Organisation of rebreather manufacturers
Rebreather endurance – The duration that a rebreather can adequately supply appropriate breathing gas
Rebreather head-up display – User information interface always in view of the diver
Rebreather loop – Ambient pressure breathing gas circuit
Rebreather scrubber – Component that removes carbon dioxide from exhaled gas
Rebreather Training Council (RTC) – Organisation to coordinate rebreather training standards
Reclaim helmet – Diving helmet that returns exhaled gas through a hose for recycling
Reclaim regulator – Diving regulator controlling flow of exhaled gas into low pressure exhaust return hose
Reclaim valve – Backpressure regulator controlled relative to ambient pressure for breathing gas recovery
Recompression (disambiguation) – Returning to a state of higher ambient pressure
Recompression chamber – A hyperbaric chamber used to treat divers suffering from decompression illness
Recovery breathing – Technique used by free divers on surfacing to reduce the risk of surface blackout.
Recovery of a convulsing diver – Procedure for rescue of a convulsing scuba diver from underwater
Recovery of an unresponsive diver – Procedure for rescue of a convulsing casualty from underwater
Recreational dive – Underwater dive done for recreational purposes
Recreational Dive Planner – PADI no-decompression dive table also available as a circular slide rule and electronic calculator
Recreational dive sites – Places that divers go to enjoy the underwater environment
Recreational diver certification – Certification as competent to dive to a specified standard
Recreational diver certification agency – Agencies which issue certification for competence in recreational diving skills
Recreational diver impact on reefs – Effects of scuba diving on the underwater environment
Recreational diver training – Training process for people who do not dive at work
Recreational diver – Person who engagesin underwater diving for entertainment
Recreational diving – Diving for the purpose of leisure and enjoyment, usually when using scuba equipment
Recreational diving fatalities – Deaths occurring during scuba dives
Recreational diving instructor – Person who trains and assesses recreational divers
Recreational diving service provider – Tangible and intangible goods and services provision for recreational diving tourism
Recreational diving tourism – Industry based on recreational diver travel
Recreational scuba certification levels – Competence represented by recreational scuba certification
Recreational scuba diving – Diving for leisure and enjoyment while using scuba equipment
Recreational trimix diver – Certification to dive with normoxic trimix with equivalent narcotic depth 80 ft or less
Reduced gradient bubble model – Decompression algorithm
Redundancy (engineering) – Duplication of critical components to increase reliability of a system
Redundant breathing gas supply – Scuba breathing gas reserved for an emergency
Redundant diving equipment – Equipment carried in case of failure of the primary equipment
Reef – A shoal of rock, coral or other sufficiently coherent material, lying beneath the surface of water
Reef Ball Foundation – Non-profit organization to promote artificial reef building
Reef Check – International NGO for reef conservation
Reef Life Survey (RLS) – Marine life monitoring programme based in Hobart, Tasmania
Refresher course – Training to update existing skills and knowledge
Refresher training – Training to update existing skills and knowledge
Refresher training (diving) – Checkout of skills or remedial training to bring skills back up to standard
Regulator freeze, also known as regulator freezing and regulator icing – Underwater breathing apparatus malfunction
Regulator malfunction – Failure modes for diving regulators
Regulator necklace – Safety item for scuba diving,to keep the DV near the mouth
Remotely operated underwater vehicle (ROUV or ROV) – A tethered underwater mobile device operated by a remote crew
REMUS (AUV) – Autonomous underwater vehicle series
Repetitive dive – Dive made while outgassing from a previous dive is incomplete
Repet-Up profile – Commercial diving multi-level dive profile
Repex, also known as repetitive exposure – Repeated exposure to potentially toxic concentrations of oxygen in breathing gas
Rescue bell – Diving bell for submarine rescue
Rescue diver – Recreational scuba certification emphasising emergency response and diver rescue
Rescue Diver – Recreational scuba certification emphasising emergency response and diver rescue
Rescue sling – Device used for lifting a casualty
Rescue tether – Equipment to facilitate a diver rescue
Rescue ventilation – Assisted breathing to support life
Reserve gas supply (diving) – Breathing gas supply for diving use if main supply is compromised or used uo
Reserve valve – Valve isolating access to reserve gas supply
Residual inert gas tissue loading – Gas remaining in the tissues after decompression
Residual nitrogen – Excess nitrogen remaining in body tissues after surfacing from a dive
Residual nitrogen time – Estimate of excess nitrogen remaining in tissues before repetitive dive
Resort diving – Introductory scuba diving experience
Respiration (physiology) – Exchange of gases between environment and tissues
Respiratory exchange ratio – Ratio between the metabolic production of carbon dioxide and the uptake of oxygen
Respiratory gas exchange – Process by which gases diffuse through a biological membrane
Respiratory interface – Facepiece of a breathing apparatus
Respiratory quotient – Ratio of carbon dioxide produced by the body to oxygen consumed by the body
Restriction (diving) – Space through which it is possible to pass with some difficulty
Reverse squeeze – Failure of the Eustachian tubes to open during a reduction in ambient pressure

Ri–Rn

Rip current – Water current moving away from shore
Risk assessment – Estimation of risk associated with exposure to a given set of hazards
Risk control – Process in which identified risks are reduced or mitigated
Risk management – Identification, evaluation and control of risks
RN Diving Manual – Training and operations manual

Ro

Rock bottom gas planning – Scuba gas planning based on a planned dive profile
Rocky reef – Natural reef of rock
Röjdykare – Clearance divers of the Swedish Navy
ROUV – Remotely operated underwater vehicle
ROV KIEL 6000 – Remotely operated vehicle built by Schilling Robotics, Davis, California for scientific tasks
ROV PHOCA – Remotely operated underwater vehicle of the COMANCHE type
ROV Supervisor – A senior ROV pilot appointed to supervise the ROV team
Royal Australian Navy School of Underwater Medicine (RANSUM) – Unit based in Sydney, Australia.
Royal Engineers – Engineering arm of the British Army
HMS Royal George (1756)#Salvage attempts – 100-gun first-rate Royal Navy ship of the line (1756) – Early salvage operation using bells and surface supplied divers
Royal Navy ships diver – Category of underwater diver in the Royal Navy

Ru

Rubicon Foundation – Non-profit organization for promoting research and information access for underwater diving
Rule of thirds (diving) – Rule of thumb for scuba gas management
Russian commando frogmen – Tactical scuba diving unit
Russian deep submergence rescue vehicle AS-28 – Priz-class deep-submergence rescue vehicle of the Russian Navy
Russian submarine AS-34 – Priz-class deep-submergence rescue vehicle
Russian submarine Losharik – Russian deep-water nuclear submarine

S

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Subsection: Top, Sa–Sb, Sc–Sd, Se, Sh, Si–Sj, Sk, Sl, Sm, Sn, So, Sp–Sr, St, Su, Sw, Sy

Sa–Sb

Safety culture – Risk-averse attitudes
Safety data sheet, also known as Material safety data sheet – Sheet listing work-related hazards
Safety sausage – Inflatable buoy used by a diver at the surface to indicate position to the dive boat
Safety stop – Optional decompression stop to reduce decompression stress
Salt spray aspiration – Inhalation of salt water droplets
Salt water aspiration syndrome – Rare diving disorder caused by inhaling a mist of seawater
Salvage diving – Diving work associated with the recovery of vehicles, cargo and structures
Salvage of the SS Egypt's gold – Recovery of bullion from wreck using an atmospheric pressure observation bell
Salvage operations on HMS Royal George – Early salvage operations using bells and surface supplied divers
Sappers Divers Group – Portuguese Navy's diving unit
Saturation diver – Diver registered as competent for saturation diving
Saturation diving – Diving decompression technique
Saturation diving skills – Surface-supplied diving skills specific to saturation operations
Saturation diving system – Facility for supporting saturation diving projects
Saturation diving team – Personnel supporting a saturation diving operation
Saturation spread – The topside base for saturation diving operations
Saturation system – Diving decompression system
Save Ontario Shipwrecks (SOS) – A provincial heritage NGO in Ontario, Canada
Savoie, Joe – Diver and inventor of diving helmets
Saw-tooth dive profile – Dive with several ascents and descents
S-BRUV – Stereoscopic baited remote underwater video

Sc–Sd

Science of underwater diving – Scientific concepts that are closely associated with underwater diving
Scientific diver training – Training divers who will be doing scientific work underwater
Scientific diving – Use of diving techniques in the pursuit of scientific knowledge
SCMBA – British military rebreather
Scorpio ROV – Work class remotely operated underwater vehicle
Scottish Sub Aqua Club (ScotSAC) – Scottish recreational diver training and certification agency
Screw gate carabiner – Carabiner snap hook with screw lock gate
Scrubber breakthrough – Failure mode in rebreathers when the carbon dioxide scrubber is exhausted
Scrubber endurance – The duration that a rebreather scrubber can adequately remove carbon dioxide
Scuba configuration – The arrangement of self contained breathing apparatus carried by a diver
Scuba contents gauge – Submersible pressure gauge for scuba cylinders
Scuba cylinder valve – Valve controlling flow of breathing gas into and out of a scuba cylinder
Scuba diving – Swimming underwater, breathing gas carried by the diver
Scuba diving equipment – Equipment needed for scuba diving
Scuba diving fatalities – Deaths occurring while scuba diving or as a consequence of scuba diving
Scuba diving in the Cayman Islands – Recreational diving tourism destination
Scuba Diving International (SDI) – Recreational diver training and certification agency
Scuba diving quarry – Disused and flooded quarry repurposed for underwater diving
Scuba diving skills – The skills required to dive safely using self-contained underwater breathing apparatus
Scuba diving therapy – Treatment using scuba diving activities
Scuba diving tourism – Industry based on recreational diver travel
Scuba Educators International (SEI) – Recreational diver training and certification agency
Scuba emergency procedures, also known as Scuba emergency skills – Standard procedures for use in common scuba diving emergencies
Scuba equipment – Equipment needed for scuba diving
Scuba fatalities – Deaths occurring while scuba diving or as a consequence of scuba diving
Scuba finswimming – Underwater sport discipline
Scuba gas blender – Person competent to blend breathing gases for scuba diving
Scuba gas consumption – Breathing gas used while scuba diving
Scuba gas management – Logistical aspects of scuba breathing gas
Scuba gas planning – Estimation of breathing gas mixtures and quantities required for a planned dive profile
Scuba gas reserve – Breathing gas reserved for contingencies
Scuba gear – The equipment used by a scuba diver for diving
Scuba harness – Equipment for supporting a scuba set on a diver
Scuba isolation manifold – Component used to functionally connect and disconnect scuba cylinders
Scuba manifold – Scuba component used to functionally connect diving cylinders
Scuba mouthpiece – Bite grip breathing interface on demand valve
Scuba orienteering – Underwater compass navigation and speed competition on scuba.
Scuba procedures – Standardised methods for scuba diving activities
Scuba refresher course – Coaching to restore skills and knowledge
Scuba regulator – Mechanism that controls the pressure of a breathing gas supply for scuba diving
Scuba replacement – Surface-supplied diving mode using only gas supplied from high pressure cylinders
Scuba reserve valve – Scuba gas supply valve which is opened to release the gas held in reserve
Scuba Schools International (SSI) – Recreational scuba and freediving training and certification agency
Scuba set – Self-contained underwater breathing apparatus
Scuba skills – The skills required to dive safely using a self-contained underwater breathing apparatus.
Scubapro – Brand of scuba diving equipment
SDBA – Special duty oxygen breathing apparatus, a military rebreather.

Se

Seabed mining – Mineral recovery from the bottom of the sea
Seabed tractor – Special purpose class of remotely operated underwater vehicle
Sea Dragon-class ROV – Chinese deep diving work class remotely operated underwater vehicle
Seafox drone – Remotely operated anti-mine marine drone
Seaglider – Deep diving autonomous underwater vehicle for long term missions
SeaKeys – Collaborative marine biodiversity project in South Africa
SEALAB – Experimental underwater habitats developed by the United States Navy
SEAL Delivery Vehicle – Manned wet submersible for deploying naval special forces
Sea level atmospheric pressure – Static pressure exerted by the weight of the atmosphere at sea level
SeaPerch – Remotely operated underwater vehicle educational program
Sea Pole-class bathyscaphe – Chinese bathyscaphe class
Sea Research Society – American nonprofit for marine research
SEAL Delivery Vehicle (SDV) – Manned wet submersible for deploying naval special forces
Search and recovery diver – Diver certified as trained in underwater search and recovery
Willard Franklyn Searle – US Navy ocean engineer and developer of diving and salvage equipment and systems
Seasickness, also known as Motion sickness – Motion sickness occurring at sea
Secondary regulator second stage – Second demand valve on a scuba regulator first stage
Self-propelled hyperbaric lifeboat (SPHL) – Powered hyperbaric evacuation unit
Self-reliant diver – Recreational diving certification
Self-reliant diving – Philosophy and practice of diving that does not rely on assistance
Self-rescue diver – Recreational diving certification
Self-sufficient diver – Recreational diving certification
Self-sufficient diving – Scuba diving with skill and equipment to manage most contingencies without assistance
Semi-submersible platform – Marine vessel used in offshore roles with good stability and seakeeping
Sentry (AUV) – Autonomous underwater vehicle made by Woods Hole Oceanographic institution
Sewer diving – Diving for maintenance work in sewers

Sh

Shadow Divers – Book by Robert Kurson recounting the discovery of a World War II German U-boat wreck
Shallow-water blackout, also known as shallow water blackout – Loss of consciousness at a shallow depth during a dive
Shallow Water Combat Submersible – Manned submersible and a type of swimmer delivery vehicle
Shallow-water diving helmet, also known as shallow water helmet – Open-bottom diving helmet held on by weight
Shark baiting – Attracting sharks by chumming the water
Shark cage diving – Diving inside a protective cage to observe sharks in the wild
Shark-proof cage – A metal structure to protect divers and snorkellers from potentially dangerous sharks
Shark River Reef – Artificial reef off New Jersey
Shark tourism – Tourism industry based on viewing wild sharks
Shayetet 13 – Special operations unit of the Israeli Navy
Shearwater Research – Canadian manufacturer of dive computers and rebreather electronics.
Shilling, Charles Wesley – U.S. Navy physician, researcher, and educator
Ships husbandry – Maintenance and upkeep of ships
Ships husbandry diving – Diving related to the maintenance and upkeep of ships
Shot-line, also known as shot line or shotline – Substantial weighted near-vertical line with buoy

Si–Sj

Sidemount – Diving equipment configuration where scuba sets are clipped to the diver's sides
Sidemount diver – Scuba certification for using scuba sets clipped to the sides of the harness
Sidemount diving – Diving using equipment configuration where scuba sets are clipped to the diver's sides
Side-mount scuba – Scuba sets carried clipped to the sides of the diver's harness
Side-slung bailout set – Bailout cylinder clipped to the side of the diver's back-mount cylinder harness
Siebe, Augustus – British engineer mostly known for his contributions to diving equipment
Siebe Gorman – British manufacturer of diving equipment and salvage contractor
Siebe Gorman CDBA – Type of diving rebreather used by the Royal Navy
Siebe Gorman Salvus – Industrial rescue and shallow water oxygen rebreather
Signal tube – Inflatable buoy used by a diver at the surface to indicate position to the dive boat
List of signs and symptoms of diving disorders – Evidence of physiological disorders resulting from underwater diving
Silt out, also known as siltout, or silt-out – Reduction of underwater visibility by disturbing silt deposits
Silt screw – A peg for insertion into soft sediment to locate a distance line
Single atmosphere diving suit – Articulated pressure resistant anthropomorphic housing for an underwater diver
Single-hose diving regulator, also known as single hose – Regulator with two stages connected by a low-ressure hose
Single point of failure – A part whose failure will disrupt the entire system
The Silent World: A Story of Undersea Discovery and Adventure – Book by Jacques-Yves Cousteau and Frédéric Dumas
Siluro San Bartolomeo – Italian manned torpedo design of late WWII
Single point of failure – A part whose failure will disrupt the entire system
Sinking of MV Conception – 2019 maritime disaster
Sinking of the Rainbow Warrior – 1985 covert attack by French foreign intelligence service on a Greenpeace ship
Sinking ships for wreck diving sites – Scuttling old ships to produce artificial reefs
Sinus squeeze – Barotrauma of the sinuses
Sistema Huautla – Cave system in Oaxaca, Mexico
Sistema Nohoch Nah Chich – Flooded cave system in Mexico
Sistema Ox Bel Ha – Flooded cave system in Quintana Roo, Mexico
Situation awareness – Adequate perception of environmental elements and external events
Siva (rebreather) – Range of military rebreathers
SJT-class ROUV – Series of Chinese remotely operated underwater vehicles

Sk

Skandalopetra diving – Freediving using a stone weight at the end of a rope to the surface
Skin bend – Decompression symptoms in superficial tissues
Skindiving (disambiguation)

Sl

Sladen Suit – Early British military drysuit
Sling (rigging) – Rope, webbing, wire or chain used to support a load for lifting
Sling cylinder – An independent scuba set carried clipped to the side of a scuba diver's harness
Slingshot valve – Dual outlet scuba cylinder valve with Y-shape body

Sm

Smith, Gordon – Inventor of KISS diving rebreather, born 1950

Sn

Snag-line search – Use of a taut line towed across the search area to catch on the target
Snell's law, also known as Law of refraction – Formula for refraction angles
Snoopy loop, also known as ranger band – Rubber band made from inner tube
Snorkel – Tube for breathing face down at the surface of the water
Snorkel mask – Breathing apparatus for surface swimming
Snorkeling – Swimming while inhaling through a snorkel
Snorkeling vest, also known as snorkelling vest – Personal buoyancy aid for use while snorkeling
Snuba – Limited depth airline breathing apparatus towed by the diver

So

Society for Underwater Historical Research – Amateur maritime archaeology organisation in South Australia
Solo diver – Recreational diver diving without a dive buddy
Solo Diver – SDI recreational diver self-sufficiency certification
Solo diving – Recreational diving without a dive buddy
Solo diving skills – Additional scuba skills of self-reliance
Solubility – Capacity of a substance to dissolve in a homogeneous way
Solution – Homogeneous mixture of a solute and a solvent
Sonar – Acoustic sensing method
Sonar imaging – Constructing digital images from sonar data
Sonic orifice – Orifice undergoing choked flow of a compressible medium
South African Association for Marine Biological Research (SAAMBR) – Non profit conservation research organisation based in Durban, SA
South African Department of Employment and Labour – Department of the South African government responsible for matters related to employment
South African Environmental Observation Network (SAEON) – A network to perform long-term ecological research in South Africa and surrounding waters
South African Underwater Sports Federation (SAUSF) – Official World Underwater Federation representative body in the Republic of South Africa
South Pacific Underwater Medicine Society (SPUMS) – Publisher for diving and hyperbaric medicine and physiology
South Pacific Underwater Medical Society Journal – Journal covering underwater and hyperbaric medicine and physiology
Southern African Underwater and Hyperbaric Medical Association (SAUHMA) – Special interest group of the Council of the South African Medical Association

Sp–Sr

SP-350 Denise – French two-person submarine
Spearfisherman (company) – American diving equipment manufacturer
Spearfishing – Hunting for fish using a spear
Speargun – Underwater fishing implement
Special Actions Detachment – Special operations maritime unit of the Portuguese Navy
Special Air Service – Special forces of the British Army
Special Air Service Regiment – Special forces unit of the Australian Army
Special Boat Service – Special forces unit of the Royal Navy
Special Duties Unit – Hong Kong Police tactical unit
Special Forces Command (Turkey) – Turkish special forces group
Special Forces Group (Belgium) – Special forces unit in the Belgian Armed Forces
Special Operations Battalion (Croatia) – Special forces military unit
Special Service Group (Navy) – The special operations force of the Pakistan Navy
Special Warfare Diving and Salvage – Bangladesh Navy special operations force
Speleonaut – Diver propulsion vehicle designed for cave exploration by a disabled diver
Spindle (vehicle) – Ice penetrating two-stage autonomous underwater vehicle
Spiral box search – Search pattern expanding stepwise outward from datum
Spitcock – Valve on diving helmet to provide water for the diver to spit on inside of viewport
Sponge diving – Diving to gather natural sponges
Sport (shipwreck) – Tugboat wrecked in Lake Huron
Sport diving (sport) – Underwater sport using recreational open circuit scuba equipment in a swimming pool
SPP-1 underwater pistol – Soviet four-barreled underwater dart pistol
SPUMS – Publisher for diving and hyperbaric medicine and physiology
SPURV – Self propelled underwater research vehicle built in 1957 for the US Navy
SPURV II – Special purpose underwater research vessel built to srudy submarine wakes
Squeeze (diving) – Barotrauma of descent
SRV-300 – Deep-submergence rescue vehicle

St

Stabilizer jacket – Configuration of diving buoyancy compensator
Stage cylinder – Diving cylinder intended to be collected for use on the return part of a scuba dive
Staged deccompression, also known as stage decompression – Decompression with stops at specific depths
Stage drop, also known as stage-drop – Placing a scuba cylinder at the distance line for planned later use.
Stage rigging (scuba) – Clips, cords and straps on a scuba cylinder to attach it to a diver
Stage set (scuba) – Scuba set to be used during a stage of a dive
Standard diving dress – Copper helmet with rubberised canvas diving suit and weighted boots
Standard diving equipment – Copper helmet with rubberised canvas diving suit and weighted boots
Standard diving helmet – Copper free-flow helmet system used with Standard Diving Dress
Standard helmet – Helmet of standard diving dress
Standard operating procedure – Set of detailed instructions to assist in workplace safety
Standard procedure – A recommend way to do something that is known to be effective and safe
Standby diver, also known as stand-by diver – Diver who is ready to go to the assistance of the working diver
Standard diving dress – Copper helmet with rubberised canvas diving suit and weighted boots
Standard operating procedure – Set of detailed instructions to assist in workplace safety
Star Canopus diving accident – Fatal offshore diving bell accident in 1978
Static apnea – Stationary diving discipline of holding breath underwater
Stena Seaspread diving accident – Saturation diving bell incident with successful rescue in the North Sea in 1981
Stratification – Layering of a body of water due to density variations
Stress exposure training – Training in a deliberately distracting environment
Striver (bathyscaphe), also known as Struggler (bathyscaphe) – Chinese deep submergence vehicle

Su

Sub-Aqua Association (SAA) – British recreational diver training and certification organisation
Submarine emergency gas supply – Breathing gas system installed in submarine for emergency use
Submarine Escape Immersion Equipment – Whole-body exposure suit that allows submariners to escape from a sunken submarine
Submarine escape set – Self contained breathing apparatus providing gas to escape from a submerged submarine
Submarine escape training facility – Facility used for training submariners in methods of escape from a sunken submarine
Submarine Escape Training Facility (Australia) – Shore facility of the Royal Australian Navy
Sub Marine Explorer – Early submarine craft
Submarine pipeline – Pipeline that is laid on the seabed or below it inside a trench
Submarine Products – Former British diving equipment manufacturer and distributor.
Submarine rescue – Rescue of personnel from a disabled submarine
Submarine Rescue Diving Recompression System – Remotely operated vehicle for rescue of personnel from sunken submarines
Submarine rescue ship – Support ship for submarine rescue and deep-sea salvage operations
Submersible pressure gauge – Pressure measuring instrument for underwater service
Subskimmer – Submersible diver propulsion vehicle with inflatable buoyancy for surface use
Subsurface (software) – Open source software for logging and planning scuba dives
Suit squeeze – Barotrauma caused by the folds of a diving suit piching the skin
Superoxide scrubber – Breathing gas scrubber that adds oxygen and removes carbon dioxide
Supersaturation – State of a solution that contains more solute than can be dissolved at equilibrium
Supervised diver – Minimum requirements for a recreational diver to dive in open water under direct supervision
Supply lock – Small airlock to transfer supplies between areas of different pressure
Support diver – Recreational diving equivalent of a stand-by diver
Surface blackout – Loss of consciuosness immediately following surfacing of a freediver
Surface decompression – Decompression in a diving chamber out of the water
Surface decompression on oxygen – Staged decompression obligation done in a decompression chamber
Surface interval – The time spent out of the water between dives
Surface marker buoy – Buoy towed by a scuba diver to indicate the diver's position
Surface oriented diving – Underwater diving in which the diver starts and finishes at surface pressure
Surface stand-by diver procedures – Functions of member of a professional diving team
Surface-supplied air diver – Person competent to dive with surface-supplied breathing apparatus
Surface-supplied breathing apparatus – Equipment to supply a diver with breathing gas at ambient pressure from the surface
Surface-supplied diver, also known as surface supplied diver – Underwater diver breathing gas supplied from the surface
Surface-supplied diving – Underwater diving breathing gas supplied from the surface
Surface-supplied diving emergency procedure, also known as surface-supplied diving emergency skill – Standard procedures for use in common surface-supplied diving emergencies
Surface-supplied diving equipment – Equipment used specifically for surface supplied diving
Surface-supplied diving procedures – Procedures used in the safe operation and use of surface-supplied diving equipment
Surface-supplied diving skills, also known as surface supplied diving skills – Skills and procedures required for the safe operation and use of surface-supplied diving equipment
Surface-supplied gas management – Provision of breathing gas to surface-supplied divers
Surface-supplied mixed gas diver – Person competent to dive with mixed gas from a closed bell
Surface tension – Tendency of a liquid surface to shrink to reduce surface area
Surface water searches – Procedures to find objects or persons lost at the surface of a body of water
Surface tension – Tendency of a liquid surface to shrink to reduce surface area
Surfactant – Substance that lowers the surface tension between a liquid and another material
Surfer's ear – Common name for an abnormal bone growth within the external ear canal
Surge (wave action) – The component of wave motion close to and parallel with the bottom
Sustained load cracking – Metallurgical failure mode of cracking under a prolonged static load
Suunto – Finnish manufacturer of compasses, dive computers and sports watches

Sw

Swedish Armed Forces Diving and Naval Medicine Centre – Diver education and training; diving medicine research and development
Swimfin – Finlike accessories worn on the feet, used for swimming, snorkeling and diving propulsion
Swimming – Self propulsion of a person through water
Swimming-induced pulmonary edema – Body fluid in the lungs while swimming.
Swim-through – Short underwater tunnel with adequate clearance and obvious exit

Sy

Systemic circulation – Portion of the cardiovascular system which transports oxygenated blood away from the heart
Systems technician – Person related to diving systems

T

Contents: Top	0–9	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z	References

Subsection: Top, Ta, Te, Th, Ti, To, Tr, Tu, Tw, Ty

T1200 Trenching Unit – Remotely operated seabed trenching unit

Ta

Tactical Divers Group – Special operations force of the Argentine Navy.
Taifib – Indonesian amphibious reconnaissance unit
Talus cave – Type of cave
Tank weight – Ballast weight attached to a scuba cylinder
Taravana – Decompression sickness after breath-hold diving
Task loading – Relationship between operator capacity and the accumulated activities that must be done

Te

Teaching method – Principles and methods used by teachers to enable student learning
Team redundancy – System for sharing backup equipment and skill diversity
Technical diver training – Processes to develop skills and knowledge to dive safely for technical diving
Technical diving – Extended scope recreational diving
Technical Diving International (TDI) – Technical diver training and certification agency
Technical Extended Range (TXR) – Recreational scuba and freediving training and certification agency
Tektite habitat – Undersea laboratory and experimental habitat
Temperate reef – Hard benthic substrate and ecosystems in cool to cold water in middle latitudes
Temperature – Physical quantity of hot and cold
Tension-leg platform – Type of offshore platform used in production of oil or gas
Tesei, Teseo – Italian naval officer and pioneering military diver
Test of pressure – Diagnostic technique to identify decompression sickness
Testing and inspection of diving cylinders – Periodical inspection and testing to revalidate fitness for service
Tethered ascent, also known as emergency tethered ascent, buoyant tethered ascent – Positive buoyancy emergency ascent using a reel upline (for CMAS Self-Reliant Diver)
Texas Finswimming Association – Official governing body for competitive and recreational finswimming in Texas

Th

Thalmann algorithm – Mathematical model for diver decompression
Thalmann, Edward D. – American hyperbaric medicine specialist and decompression researcher
Tham Luang cave rescue – 2018 international rescue in Thailand
The Darkness Beckons – History of UK cave diving by Martyn Farr
The Last Dive – Non-fiction book by Bernie Chowdhury about a double wreck diving fatality
Therapeutic decompression tables – Planned hyperbaric exposure profiles to treat decompression sickness
Therapeutic recompression – Recompression to reduce symptoms of decompression illness
Thermal balance of the underwater diver, also known as thermal balance of divers – Conditions in which the temperature of a diver can remain stable
Thermal balance of the saturation diver – Maintaining body heat in the saturation diver
Thermal comfort zone (TCZ) – Range of temperature and humidity comfortable for people
Thermal neutral zone (TNZ), also known as thermoneutral zone – Minimal metabolic regulation to retain ambient core body temperature
Thermal undersuit – Insulating undergarments for use with a dry suit
Thermocline – Distinct layer of temperature change in a body of water
Thermodynamic model of decompression, also known as Thermodynamic decompression model – Early model in which decompression is controlled by volume of gas bubbles forming in tissues
Theseus (AUV) – Large autonomous underwater vehicle for laying fibre-optic cable
The Shaft (sinkhole) – Karst feature in South Australia
The Silent World – 1956 French documentary film co-directed by Jacques Cousteau and Louis Malle
The Silent World: A Story of Undersea Discovery and Adventure – Book by Jacques-Yves Cousteau and Frédéric Dumas
Three bolt equipment – Standard diving dress using three bolts to clamp the helmet bonnet to the corselet
Three Star Diver – Fully trained and experienced recreational diver
Through-water communications – Wireless diver voice communications equipment

Ti

Tidal race – Fast-moving tidal flow passing through a constriction, forming waves, eddies and strong currents
Tide – Rise and fall of the sea level under astronomical gravitational influences
Tillman, Albert – American educator and underwater diver
Timeline of diving technology, also known as Timeline of underwater diving technology – Chronological list of notable events in the history of underwater diving equipment
Time to surface (TTS) – Estimated ascent and decompression time from a given point on a dive profile
Tissue (biology) – Group of similar cells performing a specific function
Tissue gas loading – Amount of gas dissolved in a tissue
Tissue slab decompression model – A diffusion limited series tissue decompression model
Tissue slab diffusion model – Diffusion limited series tissue decompression model

To

Torricellian chamber – Type of cave chamber
Total Nitrogen Time (TNT) – Equivalent pressure exposure estimate for a repetitive dive
Touboulic, Pierre-Marie – French engineer, inventor and writer
Tourism on the Great Barrier Reef – Service industry in Australia involving recreational diving
Towboard – Underwater survey equipment used to tow a diver

Tr

Training dive sites – Underwater environments selected as suitable for diving skills training
Transfer under pressure – Moving between pressurised vessels without decompression
Transfer under pressure diving – Surface oriented diving from a closed bell and a chamber for decompression
Travel gas – Gas breathed during the descent part of a dive
Tremie – Equipment for underwater concrete placement
Trial diving – Introductory scuba diving experience
Tribonucleation – Mechanism for creation of microbubbles
Trieste II – US Navy's second bathyscaphe
Triger, Jacques – French geologist who invented the pressurised caisson (1801–1867)
Trim weights (diving) – Diving weights distributed primarily to improve trim
Trimix blender – Person competent to blend trimix breathing gases for scuba diving
Trimix (breathing gas) – Breathing gas consisting of oxygen, helium and nitrogen
Trimix Scuba Association (TSA) – Recreational technical scuba training and certification agency
Trongle – Device used on submarines to help swimmers to locate a submerged submarine
Tropical coral reef – Reefs built by warm-water coral species
Try-dive – Supervised diving experience to try out diving or equipment

Tu

Tubesuit – Active heat transfer undergarment
Turbidity – Cloudiness of a fluid
Turkish Underwater Sports Federation (TSSF), also known as Türkiye Sualtı Sporları Federasyonu – Turkish national governing body for underwater sport and lifesaving
Turn pressure – Gas pressure at which the divers start the return from a dive

Tw

Twin bladder buoyancy compensator – Scuba diving buoyancy compensator with redundant air bag
Twin-hose regulator – Scuba regulator with two ambient pressure hoses to the mouthpiece

Ty

Type 1 wet bell – Open diving bell without onboard gas panel
Type 2 wet bell – Diving bell with onboard gas panel
Type 904 dive tender – Chinese class of naval diving support vessel

U

Contents: Top	0–9	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z	References

Subsection: Top, Um, Un, Up, Us, Uw

Um

Ultra deep air diving – Scuba diving on air to very dangerous depths
Umbilical cable – A cable and/or hose bundle which supplies required consumables to a remote user
Umbilical management – Safe handling of the diver's umbilical
Umbilical tending – Management of the supply end of the diver's umbilical

Un

Uncontrolled buoyant ascent – Type of diving accident
Uncontrolled decompression – Unplanned drop in the pressure of a sealed system
Undersea and Hyperbaric Medical Society (UHMS) – US based organisation for research and education in hyperbaric physiology and medicine.
Undersea Medical Society – Original name of Undersea and Hyperbaric Medical Society
The Undersea World of Jacques Cousteau – Documentary television series about underwater marine life
Undersuit – Clothing worn under a protective suit
Undertow (water waves) – Return flow below (nearshore) water waves.
Underwater – Aquatic or submarine environment
Underwater acoustic communication – Wireless technique of sending and receiving messages through water
Underwater acoustic positioning system – System for tracking and navigation of underwater vehicles or divers using acoustic signals
Underwater acoustics – Study of the propagation of sound in water
Underwater archaeology – Archaeological techniques practiced at underwater sites
Underwater archaeology techniques – Methodology used in underwater archaeology
Underwater art – Works that are designed for or performed in an underwater environment
Underwater Bike Race – Annual charity event in North Carolina
Underwater blackout syndrome – Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive
Underwater breathing apparatus – Equipment which provides breathing gas to an underwater diver
Underwater camera housing – Water and pressure resistant container for camera
Underwater citizen science – The organised collection of underwater data for scientific purposes by volunteers
Underwater computer vision – Subfield of computer vision
Underwater concrete placement – Positioning freshly mixed concrete at an underwater location where it is to set
Underwater construction – Industrial construction in an underwater environment
Underwater Construction Teams – Navy construction battalion underwater construction units
Underwater cutting and welding – Metalworking techniques used by underwater divers
Underwater cycling – Stunt in which a bicycle is ridden under water
Underwater Defence (Turkish Armed Forces) – Special operations unit of the Turkish Navy
Underwater demolition – The deliberate destruction or neutralization of man-made or natural underwater obstacles
Underwater Demolition Command – Special warfare unit of the Greek Navy
Underwater Demolition Team – US Navy special operations group
Underwater dive – Instance of underwater diving activity
Underwater diver – Person who descends below the surface to interact with the environment
Underwater diver training – Processes by which people develop the skills and knowledge to dive safely underwater
Underwater divers – People who participate in underwater diving
Underwater diving – Descending below the surface of the water to interact with the environment
Underwater diving emergency – Situation that endangers the life or health of a diver
Underwater diving environment – The underwater environment to which a diver may be exposed
Underwater diving equipment – Equipment used to facilitate underwater diving
Underwater diving hazards – Agents and situations that pose a threat to the underwater diver
Underwater diving on Guam – Recreational diving tourism destination
Underwater diving safety – Safety and risk management in underwater diving
Underwater diving terminology, also known as Underwater diving terms – Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
Underwater domain awareness – Underwater component of maritime domain awareness
Underwater environment – Aquatic or submarine environment
Underwater exploration – Investigating or traveling around underwater for the purpose of discovery
Underwater Explorers Club – British diving club, now defunct
Underwater firearm – Firearms that can be effectively fired underwater
Underwater football – Underwater team sport using snorkeling equipment and an American football
Underwater glider – Type of autonomous underwater vehicle
Underwater habitat – Human habitable underwater enclosure filled with breathable gas
Underwater hockey – Underwater sport of pushing a puck into the opposing goal
Underwater hockey in Australia – History and organisation of the sport in Australia
Underwater hockey in Turkey – History and organisation of the sport in Turkey
Underwater Hockey Wales – Welsh underwater hockey association
Underwater Hockey World Championships – International event for the sport of Underwater Hockey
Underwater ice hockey – Freediving variant of ice hockey played upside-down under the ice
Underwater inspection – Examination of underwater structure and equipment to assess condition
Underwater mining – Any mining activity done underwater
Underwater music – Music composed to be performed or heard underwater
Underwater navigator – Diver competent to navigate in open water by compass or pilotage
Underwater Offence (Turkish Armed Forces) – Special operations Forces of the Turkish Navy
Underwater orienteering – Underwater compass navigation and speed competition on scuba.
Underwater Orienteering World Championships – International sporting competition
Underwater painting – Technique of painting underwater
Underwater photography – Genre of photography
Underwater photography (sport) – Competitive underwater digital photography on scuba
Underwater Photography World Championships – International event for the sport of underwater photography
Underwater pilotage – Diver navigation using natural features
Underwater Port Security System – Defense against hostile swimmer incursions
Underwater rescue – Rescue of persons trapped underwater
Underwater rifle – A man-portable, long-barreled firearm which can be fired effectively underwater
Underwater rugby – Underwater team sport
Underwater rugby in Australia – Team breathhold underwater sport
Underwater rugby in Colombia – Regional sporting activity
Underwater rugby in the United States – Class of breathhold watersport
Underwater Rugby World Championships – International sporting competition
Underwater sculpture – Sculpture made for underwater display
Underwater search and recovery – Locating and recovering underwater objects
Underwater searches – Techniques for finding underwater targets
Underwater Society of America (USOA) – American national representative organization for underwater sport.
Underwater sports – Competitive underwater recreational activities
Underwater sports at the 2013 Bolivarian Games – Finswimming, free-diving and spearfishing events at San Lorenzo island
Underwater survey – Inspection or measurement in or of an underwater environment
Underwater surveying – Inspection or measurement in or of an underwater environment
Underwater target shooting – Breathhold underwater sport of target shooting with a speargun in a swimming pool.
Underwater tending point – Place where the diver's umbilical is restrained or controlled
Underwater vehicle – Vehicle intended to operate underwater
Underwater videographer – Diver trained in the use of video recorders underwater
Underwater videography – Electronic underwater photography concerned with capturing moving images
Underwater visibility – Distance at which an object can be seen through water
Underwater vision – The ability to see objects underwater
Underwater warfare – One of the three operational areas of naval warfare
Underwater work – Work done underwater during diving operations
Underwater wrestling (disambiguation)
Under way – State of a vessel free to move through the water
United Diving Instructors (UDI) – Recreational diver training and certification agency
United States Marine Corps Combatant Diver Course – Military diver training for the US Marines
United States Marine Corps Force Reconnaissance – USMC deep reconnaissance unit
United States Marine Corps Reconnaissance Battalions – Reconnaissance assets of Marine Air-Ground Task Force
United States military divers – Underwater divers employed by the US armed forces
United States Navy Experimental Diving Unit (NEDU) – The primary source of diving and hyperbaric operational guidance for the US Navy
United States Navy SEALs – U.S. Navy special operations force
United States Navy SEAL selection and training – Special forces unit policy and procedures
Universal Referral Program – System to complete recreational scuba training with another instructor
Unmanned diving – Underwater diving by autonomous or remotely operated vehicles

Up

Upstream scuba manifold – Manifold connecting cylinders upstream of the valve
Upstream valve – Valve which is opened against the pressure differential
Upwelling – Replacement by deep water moving upwards of surface water driven offshore by wind
URF (Swedish Navy) – Swedish submarine rescue vehicle

Us

U.S. Divers – Manufacterer of scuba diving equipment
User respiratory interface – Facepiece of a breathing apparatus
US Navy decompression models and tables
U.S. Navy Diving Manual (USNDM), also known as United States Navy Diving Manual, or US Navy Diving Manual – Training and operations handbook
U.S. Navy Experimental Diving Unit (USNEDU, NEDU) – The primary source of diving and hyperbaric operational guidance for the US Navy

Uw

Uwatec – Manufacturer of diving equipment

V

Contents: Top	0–9	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z	References

Subsection: Top, Va, Ve, Vi, Vo

Va

Valsalva device – Pad in a helmet or mask used to block the nose to assist in ear clearing
Valsalva maneuver – Technique for equalising pressure in the middle ears
Valve cracking pressure – Pressure difference needed to open a valve
Variable weight apnea – Deep freediving using a weighted sled for descent, pulling along the depth rope for ascent
Variable weight apnea without fins – Competitive freediving discipline
Variable-buoyancy pressure vessel – Type of rigid buoyancy control device
Variable-buoyancy propulsion – Use of a buoyancy engine to provide propulsion
Variable density buoyancy compensator – Equipment for controlling the buoyancy of a diver or submersible
Variable volume buoyancy compensator – Equipment for controlling the buoyancy of a diver
Varying Permeability Model – Decompression model and algorithm based on bubble physics
Vasa (ship) – 17th-century Swedish warship

Ve

Venting the rebreather loop, also known as venting the loop – Intentionally releasing gas from the breathing circuit}
Venture One diving accident – Saturation diving fatality in the North Sea in 1977
Vertical Blue – Freediving competition in The Bahamas at Dean's Blue Hole
Vertigo – Type of dizziness where a person has the sensation of moving or surrounding objects moving

Vi

VideoRay UROVs – Series of inspection class remotely operated underwater vehicles
Viewport (diving) – Transparent part of a helmet, submersible, or diving chamber
Vintage scuba – Early model scuba equipment and the ongoing activity of diving with it

Vo

Volumetric gas fraction – Dimensionless quantity
Voyage to the Edge of the World – 1976 French nature documentary
VVAL 18 – Mathematical model for diver decompression

W

Contents: Top	0–9	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V	W	X	Y	Z	References

Subsection: Top, Wa, We, Wi, Wo, Wr

Wa

Waage Drill II diving accident – Fatal saturation diving accident in the North Sea in 1975
Wall diving – Underwater diving alongside a near vertical face
WASP atmospheric diving system – Type of armoured diving suit without leg articulation
Water clarity – How deeply visible light penetrates through water
Water polo cap – Headgear used in water polo and a number of underwater sports
Waterproof digital camera – Digital still camera with inherently waterproof casing
Water safety – Human safety in the vicinity of bodies of water
Water separator – Device to remove condensed water from compressed air
Water surface searches – Procedures to find objects or persons lost at the surface of a body of water
Watertight zipper – Zipper closure which prevents water leakage when closed
Waves and shallow water – Effect of shallow water on a surface gravity wave
Wave shoaling – Effect by which surface waves entering shallower water change in wave height

We

Weight – Force on a mass due to gravity
Weight belt – A ballasted waist belt worn by a diver
Weighted boots (diving) – Shoes with heavy metal soles used as part of a diver's weights
Weighted shoes (diving) – Shoes with heavy metal soles used as part of a diver's weights
Weight harness – Webbing system to support diver ballast weights
Weight pocket – Container on diving equipment to hold ballast
Welfreighter – British midget submarine of the Second World War
Wells, John Morgan – Physiologist, aquanaut and researcher (1940–2017)
Welman submarine – Second World War one-man British midget submarine
Welsh Association of Sub Aqua Clubs – Welsh national governing body for underwater sport and recreational diving
Wet Nellie – 1976 car-shaped submarine from the James Bond film The Spy Who Loved Me
Wet sub – Ambient pressure diver propulsion vehicle
Wetsuit – Garment for thermal insulation from water
Wetsuit boots – Foam neoprene footwear for watersports
Wetsuit buoyancy – Upwards forece generated by the volume of an immersed wetsuit
Wetsuit buoyancy loss – Temporary reduction of volume due to compression at depth

Wi

Wildrake diving accident – Fatal offshore diving accident in Scotland, 1979
Willful violation – Deliberate or negligent violation of workplace rules and policies
Wind generated current – Flow in a body of water generated by wind friction on its surface
Wind wave – Surface waves generated by wind on open water

Wo

Women Divers Hall of Fame – International honor society.
Woodville Karst Plain Project (WKPP) – Project and organization to map the underwater cave systems of the Woodville Karst Plain
Work of breathing (WOB) – Energy expended to inhale and exhale a breathing gas
Working diver – The person who is intended to do the underwater work during a professional dive
Workplace health surveillance – Ongoing surveillance of workers' health
World Recreational Scuba Training Council (WRSTC) – Scuba diving standards body
World Without Sun – 1964 film by Jacques Cousteau

Wr

Wreck Alley – Area off California with several wrecks sunk as artificial reefs
Wreck diving – Recreational diving on wrecks

Y

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YMCA SCUBA Program – Defunct recreational diver training and certification agency
Yoke connector – Clamp to connect scuba regulator to cylinder valve
Yoke (diving helmet) – Component to prevent accidental removal of a diving helmet

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Of