 The boat was commissioned into the Austro-Hungarian Navy in April 1910, and served as a training boat—sometimes making as many as ten cruises a month—through the beginning of the First World War in 1914.The submarine scored most of her wartime successes during the first year of the war while under the command of Georg Ritter von Trapp.The French armoured cruiser "Léon Gambetta", sunk in April 1915, was the largest ship sunk by "U-5".