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 three war patrols, sinking a total of seven ships for . She was baited by the Q ship Princess Louise and torpedoed by at , off Fair Isle, in Shetland, Scotland. Twenty four men died and 10 survived.