Term | Explanation |
| SA | Sturmabteilungen - Storm Troopers - Hitler's unofficial army of thugs (aka Brownshirts) - disbanded after the blood purge of 1934. |
| Schnell | German word for quick. |
| Schwarze Kapelle | Black Orchestra - term used to describe a group of conspirators within the German Army who plotted to overthrow Hitler. The Schwarze Kapelle came near to assassinating Hitler on July 20th 1944. |
| SD | Sicherheitsdienst - Security Department - The Nazi Party security service, intelligence gathering and counter-espionage wings of the RSHA headed by Reinhard Heydrich. |
| SEAC | South East Asia Command (Allies). |
| Sealion | Operational code name for the planned German assault on Great Britain in 1940/41. |
| Shingle | Operational code name for the Allied landings at Anzio - January 1944. |
| SIM | Servizio Informazione Segreto - the Italian secret sevice. |
| Sledge-hammer | Operational code name for a planned Allied invasion of France in 1942. |
| SOE | Special Operations Executive - British organisation responsible for training and co-ordinating the operations of partisan groups in occupied countries. |
| SS | Schutzstaffeln - Protection Units - The principal elite organisation of the Nazi party which also included organisations such as the RSHA. |
| Stavka | The highest political-military authority of the Soviet Union. |
| Sword | Code name for the D-Day landing beaches of Lion-sur-Mer - June 1944. |
| Symbol | Code name for the Allied conference at Casablanca - January 1943. |