In October 1912, the Balkan League declared war on the Ottomans, a month before the Italo-Turkish War ended. At the time, "Mesudiye" was moored off Büyükdere, a neighborhood in Constantinople, with the torpedo boats and , stationed as a guard ship. In December, the Ottoman fleet was reorganized, with "Mesudiye" joining the newly formed Battleship Division, under the command of Ramiz Naman Bey. The division also included "Barbaros Hayreddin", "Turgut Reis", and "Asar-i Tevfik". The ship was moved to Büyükçekmece on 15 November, where she joined the rest of the fleet. Two days later, "Mesudiye" and "Barbaros Hayreddin" conducted shore bombardments in support of the Ottoman troops holding the Çatalca Line; the bombardments did not cause particularly significant material damage to the attacking Bulgarians, but it did boost Ottoman morale.