At the end of 1937 he was assigned to the Ministry of War, and in April 1939 he was appointed commander of the base set up in Bari, in preparation of the invasion of Albania. In June 1939 he assumed command of the services of the Armed Forces Command in Tirana till October, when he returned to Bari as Chief of Staff of the IX Army Corps, a post he was still holding when Italy entered World War II on 10 June 1940. On 1 January 1942 he was promoted to brigadier general and the next month he became deputy commander of the 132nd Armoured Division Ariete (General Giuseppe De Stefanis), fighting in North Africa. In June 1942 he was awarded another Silver Medal of Military Valour for his role in the battle of Gazala. On 28 June 1942 Arena replaced De Stefanis (who had been promoted to the commando of the XX Corps following the death of General Ettore Baldassarre) at the command of the "Ariete" until 25 July, when General Adolfo Infante was given command of the division. After Infante left command of the division, on 17 September 1942, Arena assumed command once again and was thus its commander during the second battle of El Alamein, in which the division was annihilated.