SM UB-91 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 11 April 1918 as SM UB-91.
On 4 October 1918 UB-91 sank the, killing among others, Yokohama Specie Bank sub-manager S. Ujie, his wife and three sons, together with bank employee Takashi Aoki and wife Sueko.[1] [2]
See main article: Type UB III submarine. She was built by AG Vulcan of Hamburg and following just under a year of construction, launched at Hamburg on 6 March 1918. UB-91 was commissioned later the same year . Like all Type UB III submarines, UB-91 carried 10 torpedoes and was armed with a 10.52NaN2 deck gun. UB-91 would carry a crew of up to 3 officer and 31 men and had a cruising range of 7120nmi. UB-91 had a displacement of 510lk=inNaNlk=in while surfaced and 640t when submerged. Her engines enabled her to travel at 13kn when surfaced and when submerged.
UB-91 was surrendered to Britain on 21 November 1918 at Harwich. She toured the South Wales ports of Cardiff, Newport, Swansea, Port Talbot and was towed to Pembroke Dock, eventually being broken up in Briton Ferry in 1921. King George V presented her deck gun to the town of Chepstow by in recognition of the bravery of William Charles Williams RN VC at Gallipoli in 1915. The gun forms part of the Chepstow War Memorial.
| Date | Name | Nationality | Tonnage[3] | Fate[4] |
|---|---|---|---|---|
| 25 September 1918 | Hebburn |  United Kingdom | 1,938 | Sunk |
| 26 September 1918 | 1,181 | Sunk | ||
| 28 September 1918 | Baldersby | United Kingdom | 3,613 | Sunk |
| 4 October 1918 | Hirano Maru |  Japan | 7,936 | Sunk[5] |