SM U-23 was one of the 329 U-boats serving in the Imperial German Navy in World War I. U-23 was engaged in the naval warfare and took part in the First Battle of the Atlantic. U-23 served on 3 war patrols, sinking a total of 7 ships for 8,822 tons. She was baited by the Q ship Princess Louise and torpedoed by HMS C27 at , between the Orkney and Shetland Islands off Fair Isle. Twenty four men died and 10 survived.