The German submarine U-8 was a Type IIB U-boat of Nazi Germany's Kriegsmarine, based at Kiel during World War II. It was one of the smaller versions, and was first launched on 16 July 1935. Its first commander was Harald Grosse. U-8 would have 18 commanders over the course of its service, the last being Jürgen Kriegshammer.

German Type IIB submarines were enlarged versions of the original Type IIs. U-8 had a displacement of 279 tonnes (275 long tons) when at the surface and 328 tonnes (323 long tons) while submerged. Officially, the standard tonnage was 250 long tons (254 t), however. The U-boat had a total length of 42.70 m (140 ft 1 in), a pressure hull length of 28.20 m (92 ft 6 in), a beam of 4.08 m (13 ft 5 in), a height of 8.60 m (28 ft 3 in), and a draught of 3.90 m (12 ft 10 in). The submarine was powered by two MWM RS 127 S four-stroke, six-cylinder diesel engines of 700 metric horsepower (510 kW; 690 shp) for cruising, two Siemens-Schuckert PG VV 322/36 double-acting electric motors producing a total of 460 metric horsepower (340 kW; 450 shp) for use while submerged. She had two shafts and two 0.85 m (3 ft) propellers. The boat was capable of operating at depths of up to 80–150 metres (260–490 ft).

The submarine had a maximum surface speed of 12 knots (22 km/h; 14 mph) and a maximum submerged speed of 7 knots (13 km/h; 8.1 mph). When submerged, the boat could operate for 35–42 nautical miles (65–78 km; 40–48 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 3,800 nautical miles (7,000 km; 4,400 mi) at 8 knots (15 km/h; 9.2 mph). U-8 was fitted with three 53.3 cm (21 in) torpedo tubes at the bow, five torpedoes or up to twelve Type A torpedo mines, and a 2 cm (0.79 in) anti-aircraft gun. The boat had a complement of twenty.

U-8 was ordered on 20 July 1934, i.e. in violation of the Versailles Treaty, which denied Germany possession of submarines. The U-boat was not laid down until 25 March 1935, and launched on 16 July 1935, within weeks of the Anglo-German Naval Agreement, which granted Germany parity with the British Empire in submarines.

Commissioned on 5 August 1935 with Kapitänleutnant Harald Grosse in command, U-8 was used as a training boat until 31 March 1945, when the U-boat was decommissioned.

U-8 was scuttled in the Raeder Lock at Wilhelmshaven on 5 May 1945.

• Helgason, Guðmundur. "The Type IIB boat U-8". German U-boats of WWII - uboat.net. Retrieved 6 December 2014.
• Hofmann, Markus. "U 8". Deutsche U-Boote 1935–1945 - u-boot-archiv.de (in German). Retrieved 6 December 2014.

53°31′N 8°10′E / 53.517°N 8.167°E / 53.517; 8.167