German submarine U-670 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 25 November 1941 at the Howaldtswerke yard at Hamburg, launched on 15 December 1942, and commissioned on 26 January 1943 under the command of Oberleutnant zur See Guido Hyronimus.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-670 had a displacement of 769t when at the surface and 871t while submerged. She had a total length of 67.1m (220.1feet), a pressure hull length of 50.5m (165.7feet), a beam of 6.2m (20.3feet), a height of 9.6m (31.5feet), and a draught of 4.74m (15.55feet). The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of NaNPS for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of 750PS for use while submerged. She had two shafts and two 1.23abbr=onNaNabbr=on propellers. The boat was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . U-670 was fitted with five 53.30NaN0 torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.82NaN2 SK C/35 naval gun, 220 rounds, and two twin 2sp=usNaNsp=us C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
Attached to 5th U-boat Flotilla based at Kiel, U-670 collided during training in the Baltic Sea with the target ship Bolkoburg and sank on 20 August 1943. Of her crew of 43, 22 survived while 21 perished in the accident.