3rd Regiment
- 1st Battalion, 258th Field Artillery (United States)
- 3/40 Evzone Regiment
- 3rd Air Reconnaissance Regiment
- 3rd Armored Cavalry Regiment (United States)
- 3rd Aviation Regiment (United States)
- 3rd Infantry Regiment (Lithuania)
- 3rd Infantry Regiment (United States)
- 3rd Kentucky Cavalry Regiment (Union)
- 3rd Kentucky Infantry Regiment (Union)
- 3rd Regiment Illinois Volunteer Cavalry
- 3rd Regiment Indiana Cavalry
- 3rd Regiment Iowa Volunteer Cavalry
- 3rd Regiment Royal Horse Artillery
- 3rd Regiment South Carolina Volunteer Infantry (African Descent)
- 3rd Serres Regiment
- 3rd Training Aviation Regiment
- Scots Guards
- The Buffs (Royal East Kent Regiment)