On 10 June 1940, Italy declared war on Britain and France, formally entering World War II. The heavy cruiser replaced "Trieste" as the squadron flagship, which in turn became the flagship of the 3rd Division, which also included "Trento" and "Bolzano". These four cruisers deployed north of Sicily to patrol for Allied vessels on Italy's first day of the war. On 31 August, the 3rd Division sortied to intercept the British convoy from Alexandria to Malta in Operation Hats, though the Italian fleet broke off the operation without encountering the merchant ships. "Trieste" arrived back in Taranto on 2 September. She was present there on the night of 11–12 November, when the British raided the port, and she emerged undamaged.