SM UC-91

Design

A Type UC III submarine, UC-91 had a displacement of when at the surface and while submerged. She had a length overall of, a beam of, and a draught of. The submarine was powered by two six-cylinder four-stroke diesel engines each producing, two electric motors producing, and two propeller shafts. She had a dive time of 15 seconds and was capable of operating at a depth of.
The submarine was designed for a maximum surface speed of and a submerged speed of. When submerged, she could operate for at ; when surfaced, she could travel at. UC-91 was fitted with six mine tubes, fourteen UC 200 mines, three torpedo tubes, seven torpedoes, and one SK L/45 or Uk L/30 deck gun. Her complement was twenty-six crew members.

The U-boat was ordered on 12 January 1916 and was launched on 19 January 1918. She was commissioned into the German Imperial Navy on 31 July 1918 as SM UC-91. As with the rest of the completed UC III boats, UC-91 conducted no war patrols and sank no ships. She sank after a collision with the steamer Alexandra Woermann on 5 September 1918 in the Baltic Sea. The salvage vessel raised the wreck the following day and was repaired. She was en route to surrender on 10 February 1919 when she foundered in the North Sea.