51st Regiment

• 51st (Highland) Searchlight Regiment, Royal Artillery
• 51st (Leeds Rifles) Royal Tank Regiment
• 51st (London) Heavy Anti-Aircraft Regiment, Royal Artillery
• 51st (Westmoreland and Cumberland Yeomanry) Field Regiment, Royal Artillery
• 51st Armoured Regiment (India)
• 51st Coast Artillery Regiment
• 51st Division (disambiguation)
• 51st Highland Volunteers
• 51st Illinois Infantry Regiment
• 51st Indiana Infantry Regiment
• 51st Infantry Regiment (United States)
• 51st New York Volunteer Infantry
• 51st Ohio Infantry
• 51st Pennsylvania Infantry Regiment
• 51st Regiment Massachusetts Volunteer Infantry
• 51st Regiment of Foot (disambiguation)
• 51st Sikhs (Frontier Force)
• 51st United States Colored Infantry Regiment
• 51st Wisconsin Volunteer Infantry Regiment