The German submarine U-8 was a Type IIB U-boat of Nazi Germany's Kriegsmarine, based at Kiel during World War II.

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.

[1] 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.