First Army
- 1st Army (Austria-Hungary)
- 1st Army (France)
- 1st Army (German Empire)
- 1st Army (Kingdom of Yugoslavia)
- 1st Army (Russian Empire)
- 1st Army (Wehrmacht)
- 1st Army (Yugoslav Partisans)
- 1st Brigade (disambiguation)
- 1st Division (disambiguation)
- 1st Group Army
- 1st Guards Tank Army (Russia)
- 1st Panzer Army
- 1st Parachute Army (Wehrmacht)
- 1st Red Banner Army
- 1st Regiment (disambiguation)
- 1st Shock Army
- First Allied Airborne Army
- First Army (Bulgaria)
- First Army (Greece)
- First Army (Hungary)
- First Army (Italy)
- First Army (Japan)
- First Army (Ottoman Empire)
- First Army (Romania)
- First Army (Serbia)
- First Army (Turkey)
- First Army (United Arab Republic)
- First Army (United Kingdom)
- First Australian Army
- First Canadian Army
- First Field Army
- First Polish Army (1920)
- First Polish Army (1944–1945)
- First United States Army
- First Western Army
- I Corps (disambiguation)
- New 1st Army