She spent her first two decades in service with the Active and Reserve Squadrons, primarily tasked with training maneuvers and exercises.

She was withdrawn from front-line duty in 1902 and thereafter employed as a training ship, though this role only lasted until 1909 when she was converted into a floating oil tank and renamed GM40.

[1] Her propulsion system consisted of two vertical compound steam engines each driving a single screw propeller.

The ship's bow and stern were not armored, but they were extensively subdivided into a cellular "raft" that was intended to reduce the risk of flooding.

Construction on Duilio proceeded much faster than on her sister; she was launched on 8 May 1876 and completed on 6 January 1880, more than two years before Enrico Dandolo would be finished.

[2] During the annual fleet maneuvers held in 1885, Duilio served in the 1st Division of the "Western Squadron"; she was joined by her sister Enrico Dandolo, the protected cruiser Giovanni Bausan, and a sloop.

Later that year, the ship was present during a naval review held for the German Kaiser Wilhelm II during a visit to Italy.

[5] For the periodic fleet maneuvers of 1897, Duilio was assigned to the First Division of the Reserve Squadron, which also included the ironclads Ruggiero di Lauria and Lepanto and the protected cruiser Lombardia.

The Italian Navy had considered rebuilding the ship along the same lines as her sister Enrico Dandolo, but the cost of the project proved to be prohibitive, and by 1902 they had abandoned the plan.