13th Regiment
- 13 Squadron (disambiguation)
- 13th Army (Soviet Union)
- 13th Battalion (disambiguation)
- 13th Brigade (disambiguation)
- 13th Cavalry Regiment (United States)
- 13th Continental Regiment
- 13th Division (disambiguation)
- 13th Group (disambiguation)
- 13th Illinois Volunteer Infantry Regiment
- 13th Infantry Regiment (Greece)
- 13th Infantry Regiment (Imperial Japanese Army)
- 13th Infantry Regiment (United States)
- 13th Iowa Volunteer Infantry Regiment
- 13th Maine Volunteer Infantry Regiment
- 13th Massachusetts Regiment
- 13th Michigan Volunteer Infantry Regiment
- 13th Parachute Dragoon Regiment
- 13th Pennsylvania Regiment
- 13th Regiment Illinois Volunteer Cavalry
- 13th Regiment Massachusetts Volunteer Infantry
- 13th Virginia Regiment
- 13th West Virginia Volunteer Infantry Regiment
- 13th Wisconsin Volunteer Infantry Regiment
- Somerset Light Infantry