"Littorio"s main armament consisted of nine 50-caliber Model 1934 guns in three triple turrets; two turrets were placed forward in a superfiring arrangement and the third was located aft. Her secondary anti-surface armament consisted of twelve /55 Model 1934/35 guns in four triple turrets placed at the corners of the superstructure. These were supplemented by four /40 Model 1891/92 guns in single mounts; these guns were old weapons and were primarily intended to fire star shells. "Littorio" was equipped with an anti-aircraft battery that comprised twelve Cannone da 90/53#Naval version /50 Model 1938 guns in single mounts, twenty /54 /54 guns in eight twin and four single mounts, and sixteen Breda Model 35 /65 guns in eight twin mounts. A further twelve 20 mm guns in twin mounts were installed in 1942. She received an EC 3 bis radar set in August 1941, an updated version in April 1942—which proved to be unsuccessful in service—and finally the EC 3 ter model in September 1942.