The ship's postwar career was limited due to a combination of drastically reduced naval budgets and the appearance of more modern ironclads.

She was launched on 1 October 1861 and was completed in May 1862; by this time, the Sardinian fleet had been reformed as the Regia Marina (Royal Navy) of the newly unified Kingdom of Italy.

Persano claimed he was simply waiting on the ironclad ram Affondatore, en route from Britain, but his inaction weakened morale in the fleet, with many of his subordinates openly accusing him of cowardice.

Persano held a council of war aboard the ironclad Principe di Carignano to determine whether he should sortie to engage Tegetthoff, but by that time, the Austrians had withdrawn, making the decision moot.

The Minister of the Navy, Agostino Depretis, urged Persano to act and suggested he capture the island of Lissa, to restore Italian confidence after their defeat at the Battle of Custoza the previous month.

[6] Formidabile was at that time in the 3rd Division, along with her sister Terribile, the ironclads Re di Portogallo and Regina Maria Pia, and the coastal defense ship Varese.

Persano ordered Formidabile to enter the harbor at Vis and attack the Madonna battery, supported by the ironclads Castelfidardo, Ancona, and Principe di Carignano.

[7] Upon entering the small harbor, the Italians found it impossible for the four ships to attack simultaneously, and so Formidabile was left to engage the Madonna battery alone.

[8] After the battle, Persano was replaced by Admiral Giovanni Vacca; he was ordered to attack the main Austrian naval base at Pola, but the war ended before the operation could be carried out.

The cuts were so severe that the fleet had great difficulty in mobilizing its ironclad squadron to attack the port of Civitavecchia in September 1870, as part of the wars of Italian unification.