At the outbreak of World War I the three ships formed the III division of the Austrian-Hungarian battle-fleet and spent most of the war based at Pola. The members of the "Erzherzog Karl" class were mobilized on the eve of the war to support the flight of and . The two German ships were attempting to break out of Messina, being chased by the French Navy and the Royal Navy, and make their way to Turkey. The breakout succeeded. When the flotilla had advanced as far south as Brindisi in south eastern Italy, the Austro-Hungarian ships were recalled. In company with other units of the Austro Hungarian Navy the class took part in the bombardment of Ancona on May 24, 1915. There they expended 24 rounds of 240 mm armor-piercing shells at signal and semaphore stations as well as 74 rounds of 190 mm shells aimed at Italian gun-batteries and other port installations.