| SAA | Small Arms Ammunition |
| SANLC | South African Native Labour Corps |
| SC | Staff Captain |
| SCF | Senior Chaplain to the Forces |
| SCULC | Sculcoates Lane |
| SD | Soldier Died Regiment records |
| Second or 2 L/T | 2nd Lieutenant |
| SGS | Surveyor-General of Supply |
| SGT | Sergeant |
| SIW | Self-Inflicted Wound |
| Sjt | Serjeant (rank, sometimes spelled Sergeant) |
| SKIPPER | Ships Captain - Merchant Navy |
| SLR | Superintendent of Light Railways |
| SMLE | Short Magazine Lee-Enfield |
| SOS | Struck off strength. Also used in usual sense (of emergency). |
| SP | Strongpoint |
| SPR | Sapper - Royal Engineers |
| SR | Special Reserve |
| SRS | Sound Ranging Section |
| SSM | Squadron Sergeant Major (cavalry) |
| ST | Street |
| Steward | Ships Steward |
| Stoker | Ships coal Stoker |
| TAT | Temporary Ambulance Train |
| TB | Temporary Base (medical) |