around the forward and aft main battery turrets. Duilio was also armed with thirteen 50-caliber guns and six 76-mm anti-aircraft guns. As was customary for capital ships of the period, she was equipped with three submerged torpedo tubes. She was protected with Krupp cemented steel manufactured by U.S. Steel. The belt armor was thick and the main deck was thick. The conning tower and main battery turrets were protected with worth of armor plating. Modifications Duilio was extensively rebuilt in 1937–1940 at Genoa. Her forecastle deck was extended further aft, until it reached the mainmast. The stern and bow were rebuilt, increasing the length of the ship to , and the displacement grew to . Her old machinery was replaced with more efficient equipment and her twenty boilers were replaced with eight oil-fired models; the new power plant was rated at and speed increased to . The ship's amidships turret was removed and the remaining guns were bored out to . Her secondary battery was completely overhauled; the 152 mm guns were replaced with twelve guns in triple turrets amidships. The anti-aircraft battery was significantly improved, to include ten guns, fifteen 54-cal. guns, and sixteen guns. Later, during World War II, four more 37 mm guns were installed and two of the 20 mm guns were removed. After emerging from the modernization, Duilios crew numbered 35 officers and 1,450 enlisted men. Service history Duilio was laid down at the Regio Cantieri di Castellammare di Stabia on 24 February 1912. She was launched on 24 April 1913, and completed on 10 May 1916. She saw no action in World War I, given the fact that the Austro-Hungarian fleet, Italy's main naval rival, remained in port for the duration of the conflict. In addition, Admiral Paolo Thaon di Revel, the Italian naval chief of staff, believed that Austro-Hungarian submarines and minelayers could operate too effectively in the narrow waters of the Adriatic. The threat from these underwater weapons to his capital ships was too serious for him to use the fleet in an active way. Instead, Revel decided to implement blockade at the relatively safer southern end of the Adriatic with the battle fleet, while smaller vessels, such as the MAS boats, conducted raids on Austro-Hungarian ships and installations. Meanwhile, Revel's battleships would be preserved to confront the Austro-Hungarian battle fleet in the event that it sought a decisive engagement. As a