At the outbreak of war, Euro was part of the 2nd Squadron's 1st Division, which also included her sister ships Freccia, Lampo, and Ostro.

At the time, Euro, Dardo, Lampo, Ostro, and their sister ship Strale made up the 4th Destroyer Squadron, under the command of Capitano di fregata (Frigate Captain) F. Gambardella.

By 1915, the Lampo-class destroyers were of antiquated design and had only limited military usefulness, but during World War I, they were modified, having equipment installed to carry and lay 12 mines, drop depth charges, and tow explosive paravanes.

[5] On 9 December 1915 Euro and the destroyer Indomito escorted the auxiliary ship Sterope from Taranto, Italy, to Vlorë (known to the Italians as Valona) in the Principality of Albania.

[6] Euro was involved in a friendly fire incident on 11 March 1917 when she and the torpedo boat Airone sighted the Italian submarines F9 and F10 while steaming off Messina, Sicily.