The 320 mm naval gun was the main battery gun used to modernize Italy's World War I battleships for service during World War II. The guns were manufactured by boring out and relining the battleships' original 12"/50 (30 cm) built-up guns and modifying the turrets to increase elevation above the original 20° maximum. Each ship carried two 548-tonne twin turrets and two 745-tonne triple turrets. All guns used pneumatically operated side-swing Welin breech blocks. Each barrel could fire two rounds per minute.