| R | Report |
| R & D | Research and development |
| R & M | Reliability and maintainability |
| R of N | Range of neap tides |
| R of T | Range of tides |
| R/T | Radio telephony |
| RA | Radio altimeter |
| Reinforced alert |
| RAC | Rules of the air and air traffic services |
| RACE | Research for advanced communications in Europe |
| RACP | Regional airspace control plan |
| rad | Radian |
| Radius |
| Unit of radiation |
| radar | Radio detection and ranging |
| radhaz | Radiation hazard |
| RADIAC | Radioactivity detection, identification and computation |
| radnet | Radar network |
| RADOC | Regional air defence operations centre |
| RADSL | Rate-adaptive digital subscriber line |
| RAE | Royal Aerospace Establishment |
| RAeS | Royal Aeronautical Society |
| RAF | Royal Air Force |
| RAFA | Royal Air Force Association |
| RAG | Returned ammunition group |
| RAID | Redundant array of independent disks |
| RAL | Rutherford Appleton Laboratory |
| RAM | Radar-absorbent material |
| Random access memory |
| Reliability, availability and maintainability |
| RAMIT | Rate-aided manually implemented tracking |
| RAMPS | Rapid message preparation system |
| RAN | Regional air navigation |
| RAOC | Regional air operations centre |
| RAOP | Regional air operation plan |
| RAP | Recognised air picture |
| Regimental aid post |
| Reliable acoustic path |
| Rocket assisted projectile |
| RARDE | Royal Armament Research and Development Establishment |
| RAS | Radar advisory service |
| Replenishment at sea |
| RASP | Recognised air and surface picture |
| RAT | Rocket-assisted torpedo |
| RATCC | Regional air traffic control centre |
| RATE | Radar automatic track extractor |
| RATO | Rocket-assisted take-off |
| RAWS | Role-adaptable weapon system |
| RBO | Radio beacon, omnidirectional |
| RBS | Radar bombardment system |
| RCC | Rescue co-ordination centre |
| RCDS | Raster chart display system |
| RCF | Radio communication failure |
| RCM | Radar counter-measures |
| Reliability-centred maintenance |
| RCMDS | Remote-control mine disposal system |
| RCMS | Radar control and monitoring system |
| Remote control and monitoring system |
| RCO | Route charges office |
| RCP | Remote control panel |
| RCS | Explosives (cargo) |
| Radar cross-section |
| Remote control system |
| Round-cornered square (raw materials) |
| RCV | Remotely controlled vehicle |
| RCZ | Rear combat zone |
| RD | Relative density |
| RD & P | Research, development and production |
| RDBMS | Relational data base management system |
| Remote data base management system |
| RDCE | Radio distribution and control equipment |
| RDD | Required delivery date |
| RDF | Radio direction finding |
| Rapid deployment force |
| Resource description framework |
| RDP | Radar data processor |
| RDPS | Radar data processing system |
| RDS | Radio data system |
| RDT & E | Research, development, testing and evaluation |
| rebro | Rebroadcast |
| REC | Radio-electronic combat |
| rec | Receiver |
| Recovery |
| recce | Reconnaissance |
| RECS | Radio-electronic combat support |
| ref | Reference |
| regt | Regiment |
| REIL | Runway end identifier lighting |
| rep | Reporting point |
| Representing |
| replen | Replenishment |
| reqd | Required |
| RES | Radar environment simulation |
| Radiation exposure state |
| rev/min | Revolutions per minute |
| RF | Radio frequency |
| Reconnaissance fighter |
| RFB | Request for bid |
| RFC | Request for change |
| RFI | Radio frequency interference |
| Request for information |
| RFID | Radio frequency identity (tag) |
| RFIT | Radio frequency identification tag |
| RFP | Request for proposal |
| RFQ | Request for quotation |
| rft | Reinforcement |
| RG | Radio direction-finding station |
| RGB | Red, green, blue |
| RGPO | Range-gate pull-off (radar) |
| RGX | High explosives (cargo) |
| RH | Radar head |
| Relative humidity |
| Right-hand |
| RHAW | Radar homing and warning |
| RHI | Relative height indicator |
| RHQ | Regimental headquarters |
| RI | Routing indicator |
| Royal Institution |
| RIB | Rigid inflatable boat |
| RICE | Rationalised integrated communications system |
| Rationalised internal communications equipment |
| RIMM | RAM bus in-line memory module |
| RIN | Royal Institute of Navigation |
| RINA | Royal Institution of Naval Architects |
| RIP | Radar improvement plan |
| Radiological information plot |
| RIS | Radar information service |
| RISC | Reduced instruction set computer |
| RIV | Rapid intervention vehicle |
| RIW | Reliability improvement warranty |
| RL | Rocket launcher |
| RLE | Relative luminous efficiency |
| RLG | Ring laser gyroscope |
| RLGN | Ring laser gyro navigation |
| RLP | Rail loading point |
| RLS | Rail loading system |
| RLT | Regimental landing team |
| RM | Relative motion (radar) |
| Requirements manager |
| Royal Marines |
| RMAS | Royal Maritime Auxiliary Service |
| RMCDE | Radar message conversion and distribution equipment |
| RME | Resident maintenance engineer |
| RMI | Radio magnetic indicator |
| RMP | Recognised maritime picture |
| RMPA | Replacement maritime patrol aircraft |
| RMS | Remote manipulator system |
| Royal Mail Ship |
| Royal Meteorological Society |
| rms | Root mean square |
| RN | Royal Navy |
| rnav | Radio navigation |
| RNC | Raster nautical chart |
| RNG | Radio range |
| RNLI | Royal National Lifeboat Institution |
| RO | Retired officer |
| Reverse osmosis |
| RO-RO | Roll-on, roll-off (vessel) |
| ROC | Rate of climb |
| Regional operating centre |
| ROD | Rate of descent |
| ROE | Rules of engagement |
| ROI | Return on investment |
| ROLE | Receive-only link eleven (data link) |
| ROM | Read-only memory |
| ROP | Responsible operator position |
| Runway observation post |
| ROPS | Roll-over protection system |
| ROR | Range-only radar |
| ROV | Remotely operated vehicle |
| RP | Release point |
| Reporting post |
| Reprovisioning |
| RPG | Regional planning group |
| Rocket-propelled grenade |
| RPGT | Radar procedures ground trainer |
| rpm | Revolutions per minute |
| RPOA | Recognised private operating agency |
| RPP | Regional priority plan |
| RPT | Rapid prototyping technology |
| RPV | Reactor pressure vessel |
| Remotely piloted vehicle |
| RR | Regional reinforcement |
| Restorative refit (ship repair) |
| RRC | Radio relay centre |
| RRH | Remote radar head |
| RRIM | Reinforced reaction injection moulding |
| RRL | Radio relay link |
| RRP | Rapid reinforcement plan |
| RRR | Rapid runway repair |
| RRS | Replacement radar station |
| RRT | Railroad transport |
| RS | Royal Society |
| RSB | Regional shipping board |
| RSC | Reinforcement support category |
| RSP | Responder beacon |
| RSPL | Recommended spare parts list |
| RSR | En-route surveillance radar |
| Required supply rate |
| RSRE | Royal Signals and Radar Establishment |
| RSST | Radar surveillance system test |
| RT | Radio telephone |
| Road transport |
| RTC | Radio transmission control |
| RTCA | Radio Technical Commission for Aeronautics |
| RTE | Radio trunk extension |
| Rail transfer equipment |
| RTF | Radio telephone |
| Rich text format |
| RTIP | Radio target identification point |
| RTL | Resistor-transistor logic (circuit) |
| RTM | Ready to move |
| Resin transfer moulding |
| RTO | Rail transport office |
| Railway traffic officer |
| Rejected take-off |
| RTOW | Regulated take-off weight |
| RTS | Radar tracking system |
| Request to send |
| RTT | Radio teletypewriter |
| RTTS | Royal Air Force transportable telecommunication system |
| RTU | Return to unit |
| RUM | Remote underwater manipulation |
| RV | Re-entry vehicle |
| RVD | Residual vapour detector |
| RVDT | Rotary variable displacement transducer |
| RVR | Runway visual range |
| RVSM | Reduced vertical separation minimum |
| RVU | Radar viewing unit |
| RW | Radiological warfare |
| Riveted and welded |
| Rotating pattern radio beacon |
| RWI | Radar warning installation |
| RWR | Radar warning receiver |
| rwy | Runway |
| RX | Receiver (radio) |
