Term | Explanation |
| D-Day | The first day of the Allied invasion of Normandy - June 6th 1944 - D stands for Day. |
| Demon | Operational code name for the British evacuation of Greece in April 1941. |
| Diadem | Operational code name for Allied offensive in Italy towards Rome in 1944. |
| Division | A basic army formation made up of between 12,000 and 18,000 men. |
| Downfall | Operational code name for the planned Allied assault on Japan in 1945. |
| Dragoon | Operational code name for Allied operations in the South of France formerly known as Anvil. |
| DUKW | An amphibious truck used by the Allies. |
| Dynamo | Operational code name for the British evacuation of Dunkirk in May/June 1940. |