42nd Regiment
- 42 Engineer Regiment (Geographic)
- 42 Squadron (disambiguation)
- 42nd Arkansas Cavalry Regiment
- 42nd Armoured Regiment (India)
- 42nd Battalion (disambiguation)
- 42nd Bomber Aviation Regiment
- 42nd Brigade (disambiguation)
- 42nd Deoli Regiment
- 42nd Division (disambiguation)
- 42nd Field Artillery Regiment (Lanark and Renfrew Scottish), RCA
- 42nd Group (disambiguation)
- 42nd Illinois Volunteer Infantry Regiment
- 42nd Indiana Infantry Regiment
- 42nd Infantry Regiment (France)
- 42nd Infantry Regiment (Poland)
- 42nd Infantry Regiment (United States)
- 42nd Kentucky Infantry Regiment
- 42nd Mississippi Infantry Regiment
- 42nd New York Volunteer Infantry Regiment
- 42nd Ohio Infantry Regiment
- 42nd Regiment of Foot
- 42nd Royal Tank Regiment
- 42nd United States Colored Infantry Regiment
- 42nd Virginia Infantry Regiment
- 42nd Wisconsin Volunteer Infantry Regiment
- Polish Armed Forces (Second Polish Republic)
- Second Polish Republic