The BL 4-inch gun Mk I – Mk VI were a family of early British breech-loading 4-inch naval guns.

HMS Alexandra was a central battery ironclad of the Victorian Royal Navy, whose seagoing career was from 1877 to 1900. She spent much of her career as a flagship, and took part in operations to deter the Russian Empire's aggression against the Ottoman Empire in 1878 and the bombardment of Alexandria in 1882. She was affectionately known by her crew as Old Alex.