to Italy in 1940 and was based at Messina. At the time of Italy's entrance into World War II Onice was assigned to the 13th Squadron (I Submarine Group) based at La Spezia together with and . Captain Gustavo Lovatelli was her commander and would remain in charge until October 1942. In the early stages of the war, Onice conducted some missions in the Strait of Sicily but she never even sighted an enemy ship. On September 28, 1940, while maneuvering in the port of Messina Onice collided with Diana and sustained some damage requiring repairs. Once the repairs were finished, she was deployed to Leros. In November 1940 she patrolled northwest of Alexandria. During December 21, 1940 through 1 January 1941 Onice conducted a patrol in the Aegean Sea. On March 7, 1941, Onice under command of captain Gustavo Lovatelli was sent to patrol an area north of Crete, and attack British convoys sailing between Alexandria and Piraeus during British Operation "Lustre" (transfer of 58,000 British soldiers to Greece in anticipation of a German invasion). On the night of March 8, Onice sighted several warships, including a cruiser, moving through the Strait of Kasos. She launched two torpedoes at the cruiser, but missed the target. On March 9, 1941, she returned to the base. In May 1941 she patrolled south of Strait of Kasos. In the early morning of May 21 Onice receives an order to move to a new patrol area in support of German invasion of Crete (Operation "Merkur"). At 13:15 of May 21 Onice sighted three destroyers eight miles south of the Strait of Kasos and launched three torpedoes against one of them, but the attack is unsuccessful. On September 25, 1941 Onice, while conducting an anti-submarine patrol off Benghazi along with patrol boats Zuri and Zirona, detected at 00:45 in the position a noise from diesel engines. Thinking she detected a submarine, and it's quite possible it was British submarine Thrasher, that was active in the area, Onice surfaced at 1:50 and warned Zuri and Zirona. All three ships went on a search for an enemy submarine, but they couldn't maintain contact. An incoming convoy to Benghazi consisting of ships Iseo, Capo Faro and torpedo boat Orione arrived at 2:40, and got warned about the enemy submarine presence by Onice. Actually, Thrasher already attacked the convoy earlier, but no ships were hit. On September 28,