SM U-81

SM U-81 was one of the 329 submarines serving in the Imperial German Navy (Kaiserliche Marine) in World War I. U-81 was engaged in naval warfare and took part in the First Battle of the Atlantic.

U-81 had one 10.5 cm gun with 140–240 rounds. On 8 February 1917 she torpedoed SS Mantola (1916) 143 nmi off Fastnet, forcing her crew and passengers to abandon her. She then shelled the drifting hulk until being chased away by the Acacia-class sloop sloop HMS Laburnum (1915). Mantola sank the next day. HMS E54 sank U-81 by torpedo west of Ireland on 1 May 1917. 31 of U-81's crew were killed; seven survived.

Design
Type U 81 submarines were preceded by the shorter Type UE I submarines. U-81 had a displacement of 808 t when at the surface and 946 t while submerged. She had a total length of 70.06 m, a pressure hull length of 55.55 m, a beam of 6.30 m, a height of 8 m, and a draught of 4.02 m. The submarine was powered by two 2400 PS engines for use while surfaced, and two 1200 PS engines for use while submerged. She had two propeller shafts. She was capable of operating at depths of up to 50 m.

The submarine had a maximum surface speed of 16.8 kn and a maximum submerged speed of 9.1 kn. When submerged, she could operate for 56 nmi at 5 kn; when surfaced, she could travel 11220 nmi at 8 kn. U-81 was fitted with four 50 cm torpedo tubes (one at the starboard bow and one starboard stern), twelve to sixteen torpedoes, and one 10.5 cm SK L/45 deck gun. She had a complement of thirty-five (thirty-one crew members and four officers).