# SM U-91

SM U-91 was one of the 329 submarines serving in the Imperial German Navy in World War I. U-91 was engaged in the naval warfare and took part in the First Battle of the Atlantic.

## Design

Type U 87 submarines were preceded by the shorter Type U 81 submarines. U-91 had a displacement of 757 tonnes (745 long tons) when at the surface and 998 tonnes (982 long tons) while submerged. She had a total length of 65.80 m (215 ft 11 in), a pressure hull length of 50.07 m (164 ft 3 in), a beam of 6.20 m (20 ft 4 in), a height of 9.35 m (30 ft 8 in), and a draught of 3.88 m (12 ft 9 in). The submarine was powered by two 2,400 metric horsepower (1,800 kW; 2,400 shp) engines for use while surfaced, and two 1,200 metric horsepower (880 kW; 1,200 shp) engines for use while submerged. She had two propeller shafts. She was capable of operating at depths of up to 50 metres (160 ft).
The submarine had a maximum surface speed of 15.6 knots (28.9 km/h; 18.0 mph) and a maximum submerged speed of 8.6 knots (15.9 km/h; 9.9 mph). When submerged, she could operate for 56 nautical miles (104 km; 64 mi) at 5 knots (9.3 km/h; 5.8 mph); when surfaced, she could travel 11,380 nautical miles (21,080 km; 13,100 mi) at 8 knots (15 km/h; 9.2 mph). U-91 was fitted with four 50 centimetres (20 in) torpedo tubes (two at the bow and two at the stern), ten to twelve torpedoes, one 10.5 cm (4.1 in) SK L/45 deck gun, and one 8.8 cm (3.5 in) SK L/30 deck gun. She had a complement of thirty-six (thirty-two crew members and four officers).

## Summary of raiding history

| Date | Name | Nationality | Tonnage | Fate |
| 24 December 1917 | Elmleaf | United Kingdom | 5,948 | Damaged |
| 28 December 1917 | Robert Eggleton | United Kingdom | 2,274 | Sunk |
| 2 January 1918 | Boston City | United Kingdom | 2,711 | Sunk |
| 4 January 1918 | Otto | United Kingdom | 139 | Sunk |
| 5 January 1918 | Knightsgarth | United Kingdom | 2,889 | Sunk |
| 7 January 1918 | Premier | United Kingdom | 89 | Sunk |
| 19 February 1918 | Beacon Light | United Kingdom | 2,768 | Sunk |
| 22 February 1918 | Haileybury | United Kingdom | 2,888 | Sunk |
| 23 February 1918 | Birchleaf | United Kingdom | 5,873 | Damaged |
| 23 February 1918 | British Viscount | United Kingdom | 3,287 | Sunk |
| 24 February 1918 | Renfrew | United Kingdom | 3,830 | Sunk |
| 2 March 1918 | Bessy | United Kingdom | 60 | Sunk |
| 20 April 1918 | Florrieston | United Kingdom | 3,366 | Sunk |
| 21 April 1918 | Landonia | United Kingdom | 2,504 | Sunk |
| 21 April 1918 | Normandiet | United Kingdom | 1,843 | Sunk |
| 22 April 1918 | Baron Herries | United Kingdom | 1,610 | Sunk |
| 26 April 1918 | Ethel | United Kingdom | 100 | Sunk |
| 27 April 1918 | Gresham | United Kingdom | 3,774 | Sunk |
| 27 April 1918 | Walpas | Russia | 312 | Sunk |
| 28 April 1918 | Damao | Portugal | 5,668 | Sunk |
| 28 April 1918 | Oronsa | United Kingdom | 8,075 | Sunk |
| 28 April 1918 | Raymond | France | 109 | Sunk |
| 1 July 1918 | Westmoor | United Kingdom | 4,329 | Sunk |
| 6 July 1918 | Port Hardy | United Kingdom | 6,533 | Sunk |
| 9 July 1918 | Silvia | Italy | 3,571 | Sunk |
| 13 July 1918 | Badagri | United Kingdom | 2,956 | Sunk |
| 16 July 1918 | Fisherman | United Kingdom | 136 | Sunk |
| 25 July 1918 | Tippecanoe | United States | 6,187 | Sunk |
| 1 October 1918 | Therese et Marthe | France | 32 | Sunk |
| 2 October 1918 | Maia | France | 185 | Sunk |
| 2 October 1918 | Marie Emmanuel | France | 32 | Sunk |
| 2 October 1918 | Ave Maris Stella | France | 22 | Sunk |
| 4 October 1918 | Mercedes | Spain | 2,164 | Sunk |
| 5 October 1918 | Heathpark | United Kingdom | 2,205 | Sunk |
| 5 October 1918 | Erindring | United Kingdom | 1,229 | Sunk |
| 8 October 1918 | Cazengo | Portugal | 3,009 | Sunk |
| 9 October 1918 | Pierre | France | 354 | Sunk |
| 11 October 1918 | Luksefjell | Norway | 2,007 | Sunk |
| 14 October 1918 | Bayard | France | 55 | Sunk |