On 10 June 1940, when Italy entered the Second World War, he became Chief of Staff first of Admiral Riccardo Paladini, and then of Admiral Angelo Iachino, commanders of the 2nd Fleet. He participated in the battle of Punta Stilo and then in operations that saw the Italian fleet opposing the movements of the Mediterranean Fleet from 31 August to 1 September 1940, without meeting the enemy in battle. At the end of November he participated in the battle of Cape Spartivento. In December 1940, when the First and Second Fleet were merged into a unified battlefleet, under the command of Admiral Iachino, Accorretti assumed the position of Chief of Staff of the newly established Naval Battle Forces (F.N.B.). In this new position he collaborated with Iachino in the reorganization and transfer of personnel for the establishment of a unified command and participated in the main naval operations of 1941, such as the fruitless chase for the British squadron that had bombarded Genoa in February, and the battle of Cape Matapan in March (along with Iachino, he was one of the only two officers informed of the operation, and participated in its planning and preparation). In December he participated in the First Battle of Sirte, and after promotion to Vice Admiral in 1942 he took over the operations department at Supermarina. In April 1943 he returned to sea, taking command of the 9th Division, formed by the battleships "Vittorio Veneto" (flagship), "Littorio" and "Roma".