SM U-99[Note 1] was one of the 329 submarines serving in the Imperial German Navy in World War I. U-99 was engaged in the naval warfare and took part in the First Battle of the Atlantic.

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 45 nautical miles (83 km; 52 mi) at 5 knots (9.3 km/h; 5.8 mph); when surfaced, she could travel 10,100 nautical miles (18,700 km; 11,600 mi) at 8 knots (15 km/h; 9.2 mph).

She had a complement of thirty-six (thirty-two crew members and four officers).

[1] The Royal Navy submarine HMS J2 is credited with sinking U-99 in the Northern North Sea on 7 July 1917, although the attribution is uncertain.