Kammala wannan jumla: A karshen 1937 an sanya shi zuwa Ma'aikatar War, kuma a watan Afrilu 1939 an nada shi kwamandan sansanin da aka kafa a Bari, a shirye-shiryen
mamayewar Albania. A watan Yunin 1939 ya karbi umarnin ayyukan Rundunar Sojoji a Tirana har zuwa Oktoba, lokacin da ya koma Bari a matsayin Babban Jami'in Rundunar Sojoji na IX, wani mukamin da yake rike da shi lokacin da Italiya ta shiga yakin duniya na biyu a ranar 10 ga Yuni 1940. A ranar 1 ga Janairun 1942 an daukaka shi zuwa brigadier general kuma a watan da ya gabata ya zama mataimakin kwamandan rundunar soji ta 132 Ariete (Janar Giuseppe De Stefanis), yana fada a Arewacin Afirka. A watan Yunin 1942 an ba shi lambar yabo ta Azurfa ta Soja don rawar da ya taka a yakin Gazala. A ranar 28 ga Yuni 1942 Arena ya maye gurbin De Stefanis (wanda aka ba shi mukamin kwamandojin na XX Corps bayan mutuwar Janar Ettore Baldassarre) a matsayin kwamandan "Ariete" har zuwa ranar 25 ga Yuli, lokacin da Janar Adolfo Infante ya ba da umarnin rundunar. Bayan Infante ya bar umurnin rundunar, a ranar 17 ga Satumba, 1942, Arena ya sake karɓar umarni kuma ta haka ne ya zama kwamandanta a lokacin yakin El Alamein na biyu, wanda aka hallaka rundunar.