# Index of underwater diving: O–R

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:
There are seven sub-indexes, listed here. The tables of content should link between them automatically:
* Index of underwater diving: A–C
* Index of underwater diving: D–E
* Index of underwater diving: F–K
* Index of underwater diving: L–N
* Index of underwater diving: O–R
* Index of underwater diving: S
* Index of underwater diving: T–Z

## O

| 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 |
Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox

### Ob

* Observation bell – Closed diving bell used as an observation platform

### Oc

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os, Ou, Ov, Ox
* 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
* 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
* Ocular oxygen toxicity – Adverse effects of high oxygen partial pressure on the eyes

### Of

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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
* Ohgushi's Peerless Respirator – Underwater breathing apparatus with bite-controlled gas supply valve

### Om–On

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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 with access to breathable air of the atmosphere
* 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
* Operational safety – The absence of unacceptable risk in the presence of the associated hazards
* Operations manual – Authoritative document of how things should be done in an organisation
* Optimum scuba weighting – Weighting for scuba diving which works best most of the time

### Or

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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–Ot

* Osprey Reef – Submerged atoll northeast of Queensland, Australia
* Otic barotrauma – Pressure injury to the ear

### Ou

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* 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

Section contents: Topof section, Ob, Oc, Of, Om–On, Op, Or, Os–Ot, Ou, Ov, Ox
* Oxycheq – Manufacturer and distributor of scuba equipment
* 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 tolerance test – Test for sensitivity to hyperbaric oxygen exposure
* 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

| 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 |
Section contents: Top of section, 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 Open Water Scuba Instructor – Basic level recreational diving instructor qualification
* PADI Peak Performance Buoyancy – PADI diver with buoyancy control skill
* PADI Self-Reliant Diver – Recreational scuba qualification
* PADI training standard – Criteria governing the conduct and assessment of PADI training courses
* 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 SCR, 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* Peacock Springs – Karst flooded cave and spring system in Florida
* 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* Piccard, Auguste – Swiss physicist, inventor, and explorer
* Pillar valve – Type of scuba cylinder valve
* Pinch point hazard – Mechanical hazard which may damage or injure by reducing a gap
* Pipeline end manifold (PLEM) – Termination of a rigid pipeline
* Pirelli (rebreather) – Oxygen rebreather manufacturer

### Pn

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* Pneumofathometer – Instrument for measuring the depth of a diver by air pressure

### Po

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* 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
* Poseidon Diving Systems – Swedish manufacturer of diving equipment
* 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
* Powerhead – Specialized firearm used underwater that is fired when in direct contact with the target
* Power inflator – Low pressure gas supply valve for buoyancy compensator
* PowerSwim – Diver-powered propulsion device

### Pr

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* 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
* Pressed Steel Tank – American manufacturer of seamless steel gas cylinders
* 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
* Probabilistic decompression model – Models for decompression based on risk
* 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 diving team – Support personnel for a professional dive
* 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* 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

Section contents: Top of section, Pa, Pe, Ph, Pi, Pn, Po, Pr, Ps, Pu, Py
* Pyle stop – Type of short deep decompression stops in addition to the standard profile
* Pyle, Richard – American ichthyologist and scuba diver

## Q

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

## R

| 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 |
Section contents: Top of section, 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 Computers – Italian manufacturer of technical dive computers
* Ratio decompression, also known as Ratio deco – 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

Section contents Top of section, Ra, Re, Ri–Rn, Ro, Ru
* 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 instructor – Person certified to train and assess rebreather divers
* 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 nitrox – Scuba breathing gas of air enriched with up to 40% oxygen by volume
* 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 – Shoal of rock, coral, or other 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 diving – Recreational diving on a reef
* Reef hook – Tool used by a diver to grip a reef
* 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 – Breathing gas reserved for contingencies
* Reserve gas supply (diving) – Breathing gas supply for diving use if main supply is compromised or used uo
* Reserve pressure (scuba) – Pressure of breathing gas intended for contingency use
* 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 kick (finning) – Finning technique to move backwards
* Reverse squeeze – Failure of the Eustachian tubes to open during a reduction in ambient pressure
* Reversible myopic shift – Temporary short-sightedness due to an external cause

### Ri–Rn

Section contents: Top of section, Ra, Re, Ri–Rn, Ro, Ru
* 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

Section contents Top of section, Ra, Re, Ri–Rn, Ro, Ru
* 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
* Rouquayrol–Denayrouze – French manufacturer of standard diving equipment and an early demand regulator
* 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

Section contents: Top of section, Ra, Re, Ri–Rn, Ro, 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
| 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 |