On 25 April 1940 Brivonesi was appointed commander of the 5th Naval Division, consisting of the battleships "Duilio" and "Andrea Doria", a role he would hold till November 7, 1941. Italy entered World War II on June 10, 1940, and Brivonesi commanded the 5th Naval Division in several missions, including the Battle of Calabria; his division was also involved in the Battle of Taranto, where "Duilio" was torpedoed and heavily damaged. In the same period, Brivonesi also held for some months the rank of chief of staff of the 1st Fleet. After leaving the command of the 5th Division in November 1941, he was assigned to Supermarina as Inspector of the anti-submarine forces. He held this office until April 1943; on 1 January 1943 he was promoted to admiral. Between 1940 and 1942 he was also a member of the Naval Weapons Projects Committee and of the Superior Committee for the coordination of technical projects. On 10 April 1943 Brivonesi was given command of the Ionian and Southern Adriatic Naval Department, with headquarters in Taranto.