SM U-109[Note 1] was a Type U 93 submarine of the Imperial German Navy in World War I, taking part in the First Battle of the Atlantic.

On 28 January 1918, she was sunk in the English Channel, possibly by a mine, while diving to avoid ships from the Dover Patrol (particularly drifter H.M. Beryl III).

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.

[1] When submerged, she could operate for 50 nautical miles (93 km; 58 mi) at 5 knots (9.3 km/h; 5.8 mph); when surfaced, she could travel 9,280 nautical miles (17,190 km; 10,680 mi) at 8 knots (15 km/h; 9.2 mph).

U-109 was fitted with six 50 centimetres (20 in) torpedo tubes (four at the bow and two at the stern), twelve to sixteen 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.