SM UB-81
 SM UB-81 was a German Type UB III submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. She was commissioned into the German Imperial Navy on 18 September 1917 as SM UB-81.UB-81 was sunk 2 December 1917 by a mine at 50°27′N 0°53′W 29 crew members died in the event.