18 Squadron
- 18th Aggressor Squadron
- 18th Battalion (disambiguation)
- 18th Brigade (disambiguation)
- 18th Combat Mapping Squadron
- 18th Division (disambiguation)
- 18th Flight Test Squadron
- 18th Intelligence Squadron
- 18th Reconnaissance Squadron
- 18th Regiment (disambiguation)
- 18th Space Defense Squadron
- 18th Squadron (Belgium)
- 18th Squadron (Observation)
- Marine Tactical Air Command Squadron 18
- Marine Wing Communications Squadron 18
- No. 18 (Netherlands East Indies) Squadron RAAF
- No. 18 Squadron IAF
- No. 18 Squadron RAF
- XVIII Corps (disambiguation)