which allowed them to steam for at a cruising speed of . When operating at maximum speed, their operational radius fell to , though due to the fact that Italian naval vessels were intended to operate only within the narrow confines of the Mediterranean Sea, their relatively short cruising range was not a significant problem. Armament and armor The Zaras were armed with a main battery of eight 203 mm Mod 29 53-caliber guns in four gun turrets. The turrets were arranged in superfiring pairs forward and aft. The guns fired shells at a muzzle velocity of , with a rate of fire of about three and a half rounds per minute. The turrets allowed elevation to 45 degrees, which provided a maximum range of . Each ship carried 157 shells per gun. Like the Trentos, the Zara-class ships suffered from shell dispersion that hampered accuracy. The problem was in large part due to poor quality control in Italian munition factories, which failed to ensure tight manufacturing tolerances necessary for accurate shells. In addition, the single cradle mounts required the guns to be very close together; this caused the shells to interfere with each other in flight and contributed to the dispersion problem. In an attempt to rectify the dispersion problem, the guns were supplied with modified shells that fired at . Anti-aircraft defense was provided by a battery of sixteen 47-cal. guns in twin mounts, four Vickers-Terni /39 guns in single mounts and eight guns in twin mounts. The 100 mm guns were copies of Austro-Hungarian guns designed in 1910 by Škoda that were placed in newly designed dual-purpose mounts that elevated to 85 degrees for a maximum range of . The ships' secondary battery was revised several times during their careers. Two of the 100 mm guns and all of the 40 mm guns were removed in the late 1930s and eight 54-cal. guns were installed in their place. Two 15-cal. star shell guns were added in 1940. In 1942, the star shell guns aboard Gorizia, by this time the only surviving member of the class, were replaced with four more 37 mm guns. The following year, a battery of fourteen guns in six twin and two single mounts replaced the machine guns. The ships were protected with an armored citadel that covered the ships' vitals, including the machinery spaces and ammunition magazines. Vertical protection consisted of an