[2] In 1939 Turchese returned to active duty, and formed the 72nd Squadron (VII Submarine Group) based at Cagliari together with Diaspro, Corallo and Medusa.

She carried out her first war mission in patrol off Cap de Creus June 17–19, 1940 without sighting any enemy ships.

On July 7, 1940 Turchese together with 5 other submarines, including Ascianghi and Axum, was assigned to patrol and area south of Sardinia.

On July 12, 1940, on her return journey to Cagliari, she sighted an enemy ship which appeared to be laying mines, and launched three torpedoes at the target.

December 31, 1940 – January 12, 1941 Turchese was deployed on patrol in the Strait of Otranto along with Ambra and Filippo Corridoni to protect traffic between Italy and Albania.

In the morning of October 28, 1942 Turchese was deployed along with Brin, Corallo, Emo, Topazio and Axum south of the Balearic Islands with the task of intercepting part of Force H which left Gibraltar participating in British Operation "Baritone".

On November 8, 1942 Operation Torch was launched: more than 500 British and American vessels escorted by 350 warships began landing 107,000 troops on the coasts of Algeria and Morocco, thus opening the second front in North Africa.

On September 7, 1943, under the provisions of Zeta Plan, many Italian submarines were deployed in the Tyrrhenian Sea to intercept an anticipated Anglo-American landing in southern Italy.

On November 27, 1943 Turchese left Malta towed by corvette Chimera, first coming to Augusta then to Taranto, and finally to Brindisi.