SM UB-73 was a German Type UB II submarine, built by AG Vulcan of Hamburg, that served in the Imperial German Navy during World War I. Commissioned on October 10, 1916, UB-73 primarily operated in the Mediterranean.
The UB II type submarines were a significant improvement over the earlier UB I class, offering greater range and armament. UB-73 displaced 272 tons surfaced and 305 tons submerged. It had a crew of 1 officer and 21 men.
UB-73 was equipped with two torpedo tubes located in the bow, and carried a total of four torpedoes. It was also armed with one 8.8 cm (3.5 in) deck gun for surface engagements.
Throughout its service, UB-73 was responsible for sinking a number of Allied and neutral vessels. Details of specific attacks and vessels sunk can be found in historical records of U-boat activity in the Mediterranean theater during World War I.
After the war, UB-73 was surrendered to the Allies. The vessel was subsequently scuttled in the Mediterranean Sea. The precise location of the wreck is known, and the site has been investigated by divers.