Commissioned into service in the Italian Regia Marina (Royal Navy) in 1914, she served in World War I, playing an active role in the Adriatic campaign and seeing action in the Battle of the Strait of Otranto in 1917.

The squadron, under the command of Capitano de fregata (Frigate Captain) P. Orsini, was based at Taranto, although either Impetuoso or Indomito or both were visiting La Spezia that day.

[2] On 9 June 1915, Insidioso, Indomito, Intrepido, Impetuoso, Irrequieto, the protected cruiser Quarto, and the destroyers Animoso, Ardente, Ardito, and Audace escorted the armored cruisers Giuseppe Garibaldi and Vettor Pisani as they participated in the bombardment of the lighthouses at the Cape of Rodon and Shëngjin (known to the Italians as San Giovanni di Medua) on the coast of the Principality of Albania.

[3] On 3 December 1915 Insidioso, Impetuoso , Indomito, Intrepido, and Irrequieto got underway from Brindisi to escort one of the first supply convoys for Italian troops in Albania.

[3][4][5] On 8 December 1915, Insidioso and Impetuoso escorted the steamship Palermo, carrying over 700 men and 43 draft animals, from Taranto to Vlorë (known to the Italians as Valona) in Albania.

On the night of 11–12 December 1915 Insidioso, now under the command of Capitano di corvetta (Corvette Captain) Bucci, and Impetuoso escorted Valparaiso, loaded with troops, from Taranto to Vlorë.

[5] On 23 February 1916 Insidioso and Impetuoso bombarded Austro-Hungarian artillery positions on the mountain Sasso Bianco in the Dolomites during the evacuation of Durrës (known to the Italians as Durazzo) in Albania.

Principe Umberto sank in a few minutes about 15 nautical miles (28 km; 17 mi) southwest of Cape Linguetta with the loss of 1,926 of the 2,821 men on board, the worst naval disaster of World War I in terms of lives lost.

[4] On 11 June 1917 Insidioso, Irrequieto, and the torpedo boats Airone and Ardea provided distant support to 10 Italian seaplanes sent to bomb Durrës.

An Austro-Hungarian Navy force consisting of the scout cruiser Helgoland and the destroyers Balaton, Csepel, Lika, Orjen, Tátra, and Triglav left Cattaro on 18 October 1917 to attack Italian convoys.

At 06:30 on 19 October 1917, Insidioso, the scout cruisers Alessandro Poerio and Guglielmo Pepe, and the destroyers Pilade Bronzetti and Simone Schiaffino got underway from Brindisi to pursue the Austro-Hungarians, and the destroyers Ippolito Nievo and Rosolino Pilo and the British light cruiser HMS Weymouth diverted from a voyage from Vlorë to Brindisi to join the pursuit.