[1] After a period as a teacher at the Army War School of Turin, on 10 October 1925 he was assigned to the staff of the military division of Alessandria.

In 1942 he was appointed commander of territorial defense of Naples, a post he retained after promotion to major general on 28 March 1943 and still held at the time of the proclamation of the Armistice of Cassibile, on 8 September 1943.

[2] His forces consisted of 9,000 men – largely poorly trained and equipped territorial troops – but he did not attempt any resistance to the German takeover.

He instead forbade public gatherings "in order to avoid incidents with the Germans", threatening to have the Army fire on the crowds, ordered subordinated commands to "buy time and avoid angering the Germans", ordered the release of German soldiers who had been captured by Italian units that had engaged them on the initiative of their commanders (even returning them their weapons), and finally fled the city in civilian clothes along with his superior, General Riccardo Pentimalli, commander of the XIX Army Corps.

Deltetto, who claimed in his defense that he did not have enough men, that he had not been forewarned of the armistice and that he had not received any orders from Rome, was acquitted of the accusation of collaborationism, but sentenced to twenty years' imprisonment for "abandonment of command" on 24 December 1944.