First he launched the Buccari Raid in February of 1918, which saw three small motorboats navigate into the sheltered heart of Austrian shipping to fire torpedoes at enemy ships. This required the crews to sneak through several miles of narrow straits, where they could be fired at from both land and sea if they were noticed. The stealth mission was a success, although one of their torpedoes plowed into the beach while the rest were harmlessly caught up in anti-torpedo nets, and the warship they thought they were firing on later turned out to have only been a mothballed passenger ferry anyway. But D'Annunzio's real goal was to release three floating containers sporting the Italian flag, taunting the Austrians with the knowledge of how far they'd snuck into their territory.
The raid was a propaganda coup, but D'Annunzio wasn't done. On August 9, 1918, he was onboard one of eight planes that flew over Vienna to drop half a million leaflets on the populace below. The leaflets, some with a message written by D'Annunzio himself, mocked Austria's loyalty to Germany, and warned that the Italians could just have easily dropped bombs. The Viennese were more baffled than outraged, since D'Annunzio's leaflets had been written in Italian instead of German, and were also so full of high-minded nonsense like "The rumble of the young Italian wing does not sound like the one of the funereal bronze, in the morning sky" that they would have been incomprehensible even to most people who could speak the language. But the 1,200 km round trip was an impressive technical feat for the day, and fawning newspaper headlines all over the Allied world further boosted Italian morale.