During World War I he was the commander of several Army corps and led the Italian troops that captured Gorizia (Sixth Battle of the Isonzo). In June 1917, he reached the apex of his military career when he took command of the Second Army (Italy) and captured the Bainsizza Plateau (Eleventh Battle of the Isonzo). Later, he was removed from command after the Italian defeat at the Battle of Caporetto (October–November 1917). He had failed to check the advance of the Imperial troops (which included for the first time, German troops sent from the Western Front) before being forced to cede his command for health reasons. Capello was blamed for the defeat, and he never returned to service.