320 mm Model 1934 naval gun

Cannone navale da 320
This photo shows the typical fore-and-aft installation of a twin turret superfiring over a triple turret.
Type	Naval gun
Place of origin	Italy
Service history
In service	1937 – 1956
Used by	Regia Marina Soviet Navy Italian Navy
Wars	Second World War
Specifications
Weight	64 tonnes
Barrel length	14 meters (550 inches)
Shell	525 kilograms (1,160 lb)
Caliber	320 mm (12.6 in)
Muzzle velocity	830 meters per second (2,700 ft/sec)
Maximum firing range	30 kilometres (19 mi)

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"/46 (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.

The Conte di Cavour-class battleships Conte di Cavour and Giulio Cesare originally mounted 13 guns as built in 1915 and 1914. These ships were rebuilt between 1933 and 1937 by removing the Q triple turret amidships and replacing guns in triple A turret, twin B and X turrets, and triple Y turret. Conte di Cavour carried Vickers Mk G guns while Giulio Cesare carried Pattern T guns built by Elswick Ordnance Company. Odero Terni Orlando (OTO) re-bored the Vickers guns while the Elswick guns were re-bored by Gio. Ansaldo & C.. Maximum gun elevation was increased to 27°.

The Andrea Doria-class battleships Andrea Doria and Caio Duilio originally mounted 13 guns as built in 1916 and 1915. These ships were similarly rebuilt between 1937 and 1940 by removing Q turret and replacing guns in A, B, X, and Y turrets. Pattern T guns aboard Caio Duilio were similarly rebuilt by Ansaldo while Mk G guns aboard Andrea Doria were rebuilt by OTO. Maximum gun elevation was increased to 30°.