 After Germany 's conquest of Romania ( see Romania during World War I ) , the German Imperial Navy had sufficient fuel oil for submarines located in the Black Sea . UB @-@ 42 and three of her sister ships in the Pola Flotilla were ordered to Constantinople and , en route , had to navigate through the Dardanelles , which had been heavily mined by the Allies in the middle of 1916 . UB @-@ 42 joined the Constantinople Flotilla ( German : U @-@ boote der Mittelmeerdivision in Konstantinopal ) on 16 August . 
