During the months between the outbreak of World War I and Italy's entry into the war, there was intense political controversy in Italy between pro-war and pro-peace factions. Baracca remained aloofly neutral, but ready to serve his nation. After Italy's entry into the war on the Entente side in May 1915, he was sent to Paris to convert to Nieuport two-seaters. Upon his return in July, he was assigned to the 8a Squadriglia Nieuport.
The Nieuport 10s that equipped this squadron were almost useless against Austro-Hungarian raids; they were too slow, with too slow a rate of climb, to bring the intruders to battle with any regularity. The frustrated Italian pilots even resorted to leaving their observers ground-bound in attempts to improve performance, to little avail. On those rare occasions when battle was joined, the Nieuports' guns usually jammed. Renaming the unit to 1a Squadriglia Caccia on 1 December 1915 did nothing to solve the problems.
The Nieuport 11 single-seat fighter with Lewis guns entered service in April 1916, and on 7 April, flying this new fighter, Baracca scored his first victory, holing the fuel tank of an Austrian Hansa-Brandenburg C.I and wounding its two-man crew. This was also Italy's first aerial victory in the war. This first victory featured his favorite manoeuvre, which was to zoom in unseen behind and below an enemy and fire his machine gun from pistol range.
It was around this time that Baracca adopted as a personal emblem a black prancing horse on his Nieuport 17, in tribute to his former cavalry regiment. This prompted some to call him, "The Cavalier of the Skies". Flying the Nieuport 17 and then, from March 1917, the SPAD VII, he scored both individually, and in combination with other Italian aces.
Baracca's friend Fulco Ruffo di Calabria nearly ended Baracca's career-and life-in June 1917. Ruffo di Calabria burst out of a cloud firing in a head-on pass at an enemy airplane, and barely missed Baracca. Later, on the ground, Baracca assured his companion, "Dear Fulco, next time, if you want to shoot me down, aim a couple of meters to the right. Now let's go for a drink and not talk of it any more!"
A dedicated fighter pilot, Baracca found life away from the front unbearable and remained as much as possible with the 91st Squadriglia, even after being promoted to Maggiore in November 1917. Baracca remained a modest, sensitive man conscious of his duty and compassionate to both his squadron comrades and to his defeated enemies. He would try to visit his victims in hospital afterwards, to pay his respects, or he would place a wreath on the grave of those he killed. He had raised his score to 30 by the end of 1917.
Soon afterwards, Baracca, Piccio, and Ruffo di Calabria were tasked with evaluating the new Ansaldo A.1 Balilla fighter. Baracca was personally decorated by King Victor Emmanuel III at La Scala at this time. It was March 1918 before Baracca convinced his superiors that he belonged back at the front. He was not long back before he found himself in a situation similar to the previous late October: his squadron was forced to withdraw by enemy advances on 27 April. It was about this time that he adopted the griffin as an insignia for the planes in his unit. Most of his pilots adopted it, though some still flaunted the prancing stallion as a gesture of respect for their commander.