Launched on 24 February 1942, launched on 24 April 1913 and completed and entered service on 10 May 1915, the ship only participated in exercises, later to be rebuilt at the Ansaldo Shipyard in Genoa from 1937 until her return to service on 15 July 1940.
The RN Duilio, also known as the Caio Duilio, is the sister ship of the RN Andrea Doria. Built in the Dreadnought era, the ship did not enter the action in World War I due to Allied naval supremacy in the Mediterranean. What makes this ship special is the refit it underwent in the years between the wars. Due to the lack of other options, the Italians gave the old battleships of the Conte di Cavour class and the Andrea Doria class the most extensive modernisations ever made to any dreadnought, resulting in ships that were almost unrecognisable from before.
She was later rebuilt at the Ansaldo shipyard in Genoa from 1937 until her return to service on 15 July 1940.
The refit for this vessel consisted of Extensive modifications to the hull including a rebuild of the bow and stern, lengthening the ship by almost 11 metres, two propeller shafts removed, the old turbines replaced by new geared turbines, the ageing machinery, powerplant and all 20 old boilers were ripped out and replaced with modern systems and 8 new superheated oil-fired boilers, while the amidships main battery turret was taken out to make way for an entire rearrangement of the machinery and funnels, increasing the maximum speed by about 10km/h. The remaining main guns were bored out an extra 15 mm to allow the guns to fire heavier 320 mm shells, the turrets were retrofitted with electric power and their maximum elevation was increased, the obsolete torpedo tubes were removed, several 37 mm and 20 mm anti-air guns were added, the old casemate 152 mm guns were torn out and replaced with four forward-facing triple 135 mm turrets and several dual-purpose single-gun 90 mm turrets which were placed along the side of the superstructure, which itself was also completely rebuilt, including a new conning tower and modern rangefinding systems. The deck armour was increased to a total of 135 mm and a Pugliese torpedo defence system was installed.
The RN Duilio took part in several activities during WW2, though the ship never got a chance to engage another surface target and arguably the most interesting part of its service life was when it was torpedoed in Taranto by the British. The ship continued serving in the Italian Navy after the war and was decommissioned in late 1956, being sold for scrap the next year.
