Term | Explanation |
| Galvanic | Operational code name for the US occupation of the Gilbert Islands - November 1943. |
| GC&CS | Government Code and Cipher School - based at Bletchley Park, England |
| Gestapo | Geheime Staatspolizei - the German Secret State Police. |
| GKO/GOKO | Soviet State Defence Committee. |
| Gold | Code name for one of the landing beaches in Normandy (in the British/Canadian sector). |
| Gomorrah | Operational code name for the RAF bombing of Hamburg in July/August 1943. |
| Goodwood | Operational code name for the Allied breakout from Normandy via Caen in July 1944. |
| Gothic Line | German defence line in Italy - north of Florence. |
| Granit | Operational code name for the US operations in the Central Pacific - March 1944. |
| Greif | Operational code name for the dropping of English-speaking German Troops wearing American uniforms behind the Allied lines in the Ardennes, prior to Hitler's last offensive in the west. |
| Grenade | Operational code name for the US offensive in the Rhineland - February 1945. |
| Gustav Line | German defence line in Italy - centred on Monte Cassino. |