Mark XII or Mark 12 often refers to the twelfth version of a product, frequently military hardware. "Mark", meaning "model" or "variant", can be abbreviated "Mk."

Mark XII or Mark 12 may refer to:

• BL 6 inch Mk XII naval gun, a British naval gun
• MK-3-12 (1907), a Russian naval main weapon that used three 12-inch guns in a single mounting
• Mark 12 torpedo (1930), an American 21-inch torpedo
• 5"/38 caliber gun or Mark 12 5"/38 (1934), a widely used American 5-inch naval gun
• 18 inch Mark XII torpedo (1935), a British 18 inch torpedo
• Supermarine Spitfire Mk XII (1942–1944); the first Griffon-engined Spitfire variant
• Hawker Hurricane Mk XII (1942), a Canadian-built Hurricane variant
• Gloster Meteor Mk XII, a British night fighter variant with American radar
• 21-inch Mark 12 (1952), a British torpedo
• Mark 12 nuclear bomb (1954–1962), an American nuclear bomb
• Colt Mk 12 cannon, a US Navy aircraft gun used in the 1950s and 1960s
• Mk 12 Special Purpose Rifle (2002), a weapon system in use by United States Special Operations Forces

• Sumlock ANITA calculator Mk 12 (1966), a Sumlock ANITA desktop model

• Mark 12 or Mark XII, the twelfth chapter of the Gospel of Mark in the New Testament of the Christian Bible
• Vox Mark XII, a 12-string variant of the Vox Mark electric guitar made in the 1960s
• MK12, a graphic design company

This disambiguation page lists articles associated with the title Mark XII.
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