The incursion became the first offensive action of the Italian Navy in the conflict, and ended with the destruction of the naval outpost, the sinking of a flotilla of small vessels and the capture of the majority of the Austro-Hungarian garrison.

On 3 May 1915, as a result of the Treaty of London, signed in secrecy on 26 April, the Italy's government changed sides and lined up with the Entente Cordiale and Russia, breaking their 33-year-old ties with the Triple Alliance.

The small island of Porto Buso is located in the mouth of the river Ausa the southernmost border post of the Austro-Hungarian Empire.

[3] When it became obvious by mid-May that Italy would join the Entente, the customs outpost was reinforced by soldiers from the Imperial Army's coastal defence, along with a signals detachment from the Austro-Hungarian Navy.

The Soldato-class destroyers Bersagliere and Artigliere were ordered to shell Austro-Hungarian positions and naval assets around the town of Grado itself, while the Nembo-class Zeffiro, under the command of Captain Arturo Ciano, was in charge of the attack on Porto Buso.

Ciano immediately ordered Zeffiro's 76 mm guns to open fire on the watchtower and the jetty, hitting the outpost, several customs motorboats, and other small craft at anchor with 169 rounds.

A motorboat with two staff petty officers aboard received a direct hit from Zeffiro[9] and sank,[10] while a whaler evacuating ten customs personnel and soldiers capsized; only three of the passengers managed to survive.

The lukewarm attitude of Lieutenant Mareth, a Hungarian, was later criticised by Admiral Alfred von Koudelka, commander of the naval sector of Trieste at the time.

[12] Moreover, one of the Austro-Hungarian servicemen killed at Porto Buso was the cook Eugenio Sandrigo, from Grado, who became the first ethnic Italian to die in the war.