|Ordered:||12 January 1916|
|Builder:||Blohm & Voss, Hamburg|
|Launched:||19 January 1918|
|Commissioned:||31 July 1918|
|Fate:||sank while on way to surrender, 10 February 1919|
|Class and type:||German Type UC III submarine|
|Beam:||5.54 m (18 ft 2 in) (o/a)|
|Draft:||3.77 m (12 ft 4 in)|
|Test depth:||75 m (246 ft)|
|Notes:||15-second diving time|
A German Type UC III submarine, UC-91 had a displacement of 491 tonnes (483 long tons) when at the surface and 571 tonnes (562 long tons) while submerged. She had a length overall of 56.51 m (185 ft 5 in), a beam of 5.54 m (18 ft 2 in), and a draught of 3.77 m (12 ft 4 in). The submarine was powered by two six-cylinder four-stroke diesel engines each producing 300 metric horsepower (220 kW; 300 shp) (a total of 600 metric horsepower (440 kW; 590 shp)), two electric motors producing 770 metric horsepower (570 kW; 760 shp), and two propeller shafts. She had a dive time of 15 seconds and was capable of operating at a depth of 75 metres (246 ft).
The submarine was designed for a maximum surface speed of 11.5 knots (21.3 km/h; 13.2 mph) and a submerged speed of 6.6 knots (12.2 km/h; 7.6 mph). When submerged, she could operate for 40 nautical miles (74 km; 46 mi) at 4.5 knots (8.3 km/h; 5.2 mph); when surfaced, she could travel 9,850 nautical miles (18,240 km; 11,340 mi) at 7 knots (13 km/h; 8.1 mph). UC-91 was fitted with six 100 centimetres (39 in) mine tubes, fourteen UC 200 mines, three 50 centimetres (20 in) torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one 8.8 centimetres (3.5 in) Uk L/30 deck gun. Her complement was twenty-six crew members.
Construction and career
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.[Note 1] 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 Vulkan 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.
- "SM" stands for "Seiner Majestät" (English: His Majesty's) and combined with the U for Unterseeboot would be translated as His Majesty's Submarine.
- Bendert, Harald (2001). Die UC-Boote der Kaiserlichen Marine 1914-1918. Minenkrieg mit U-Booten (in German). Hamburg, Berlin, Bonn: Mittler. ISBN 3-8132-0758-7.
- Gröner, Erich; Jung, Dieter; Maass, Martin (1991). U-boats and Mine Warfare Vessels. German Warships 1815–1945. 2. Translated by Thomas, Keith; Magowan, Rachel. London: Conway Maritime Press. ISBN 0-85177-593-4.
- Gardiner, Robert, ed. (1985). Conway's All the World's Fighting Ships, 1906–1921. Annapolis, Maryland: Naval Institute Press. ISBN 978-0-87021-907-8. OCLC 12119866.
- Tarrant, V. E. (1989). The U-Boat Offensive: 1914–1945. Annapolis, Maryland: Naval Institute Press. ISBN 978-0-87021-764-7. OCLC 20338385.