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.
In service these guns chronically suffered of great horizontal dispersion, both from the worsened thermodynamic performance of the guns themselves and from the unequal quality of the shells fired.