In September 1915, he became commander of the Fourth Army, stationed in the Cadore. At the height of the disastrous Battle of Caporetto in the autumn of 1917, General Luigi Cadorna ordered him to retreat with his army and clear the Cadore. Unaware of the seriousness of the situation, Di Robilant hesitated to execute the order, resulting in the capture of 11,500 of his men by the forces of the German general Otto von Below. Di Robilant withdrew to the Mount Grappa massif, where he won the defensive battle of Mount Grappa.