SM U-11 or U-XI was a U-10-class submarine in the Austro-Hungarian Navy (German: Kaiserliche und Königliche Kriegsmarine or K.u.K.

[6] SM UB-15 was commissioned into the German Imperial Navy under the command of Oberleutnant zur See Heino von Heimburg on 11 April.

On 10 June, UB-15 sank the Italian submarine Medusa for a loss of 245 tons off Porto di Piave Vecchia in the Northern Adriatic.

[7][8][Note 2] Like all Type UB I and U-10 class submarines, UB-15 was equipped with compensating tanks designed to flood and offset the loss of one of the 1,700-pound (770 kg) C/06 torpedoes.

When UB-15 torpedoed and sank Medusa, the tank failed to properly compensate, forcing all of the crewmen to run to the stern to offset the trim imbalance and prevent the ship from sinking.

[11] U-11 captured one ship in her Austro-Hungarian service,[4] and was handed over to Italy as a war reparation and scrapped at Pola by 1920.