Term | Explanation |
| RAAF | Royal Australian Air Force. |
| RAF | Royal Air Force (Britain). |
| RAN | Royal Australian Navy. |
| RCAF | Royal Canadian Air Force. |
| RCN | Royal Canadian Navy. |
| Reckless | Operational code name for US operations in Hollandia, New Guinea - April 1944. |
| Red Army | The Soviet armed forces. |
| Reichstag | The German Parliament. |
| RFSS | Reichsfuehrer SS - Reich Leader SS the formal title of Heinrich Himmler. |
| RIN | Royal Indian Navy. |
| Ring | Operational code name for Soviet offensive against German army at Stalingrad - January 1943. |
| RN | Royal Navy (Britain). |
| RNZAF | Royal New Zealand Air Force. |
| RNZN | Royal New Zealand Navy. |
| RSHA | Reichssicherheitshauptamt - Reich Security Main Office - orgainisation created by Himmler to coordinate all German security and police departments including the Gestapo, Kripo and SD. |
| Rumyantsev | Operational code name for Soviet counter offensive at the battle of Kursk, following operation Citadel - August 1943. |