The First Balkan War broke out in October 1912, when the Balkan League attacked the Ottoman Empire after the war with Italy had revealed the scale of Ottoman weakness. The condition of "Barbaros Hayreddin", as with most ships of the Ottoman fleet, had deteriorated significantly. During the war, "Barbaros Hayreddin" conducted gunnery training along with the other capital ships of the Ottoman navy, escorted troop convoys, and bombarded coastal installations. On 17 October, "Barbaros Hayreddin" and "Turgut Reis" steamed to İğneada. Two days later, the two battleships bombarded Bulgarian artillery positions near Varna. On 30 October, "Barbaros Hayreddin" was back outside Varna to blockade the port along with the destroyer "Nümune-i Hamiyet". On 17 November, "Barbaros Hayreddin" and "Mesudiye" bombarded Bulgarian positions in support of I Corps, with the aid of artillery observers ashore. The battleships' gunnery was poor, though it provided a morale boost for the defending Ottoman army dug in at Çatalca. From 15 to 20 November, the ship was stationed at Büyükçekmece along with her sister ship and several other warships, but they saw no action against the small Bulgarian navy.