45th Regiment
- 45th (Leeds Rifles) Royal Tank Regiment
- 45th (Nottinghamshire) (Sherwood Foresters) Regiment of Foot
- 45th Arkansas Infantry (Mounted)
- 45th Brigade (disambiguation)
- 45th Cavalry (India)
- 45th Detached Reconnaissance Regiment
- 45th Division (disambiguation)
- 45th Garrison Regiment, Royal Artillery
- 45th Illinois Volunteer Infantry Regiment
- 45th Infantry Regiment (Imperial Japanese Army)
- 45th Infantry Regiment (United States)
- 45th Iowa Volunteer Infantry Regiment
- 45th Light Anti-Aircraft Regiment, Royal Artillery
- 45th New York Volunteer Infantry Regiment
- 45th North Carolina Infantry
- 45th Ohio Infantry
- 45th Rattray's Sikhs
- 45th Regiment Kentucky Volunteer Mounted Infantry
- 45th Regiment Massachusetts Volunteer Infantry
- 45th Squadron (disambiguation)
- 45th Tennessee Infantry Regiment
- 45th United States Colored Infantry Regiment
- 45th Virginia Infantry
- 45th Wisconsin Volunteer Infantry Regiment