|Ordered||5 June 1941|
|Laid down||13 June 1942|
|Launched||6 July 1943|
|Commissioned||20 September 1943|
|Fate||Sunk 9 April 1945|
|Class and type||Type VIIC submarine|
|Height||9.60 m (31 ft 6 in)|
|Draught||4.74 m (15 ft 7 in)|
|Complement||4 officers, 40–56 enlisted|
|Identification codes:||M 52 352|
|Commanders:||Oblt.z.S. Paul Weber|
|Operations:||1 war patrol|
|Victories:||no ships sunk|
German submarine U-677 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II. The submarine was laid down on 13 June 1942 at the Howaldtswerke yard at Hamburg, launched on 6 July 1943, and commissioned on 20 September 1943 under the command of Oberleutnant zur See Paul Weber.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-677 had a displacement of 769 tonnes (757 long tons) when at the surface and 871 tonnes (857 long tons) while submerged. She had a total length of 67.10 m (220 ft 2 in), a pressure hull length of 50.50 m (165 ft 8 in), a beam of 6.20 m (20 ft 4 in), a height of 9.60 m (31 ft 6 in), and a draught of 4.74 m (15 ft 7 in). The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2,800 to 3,200 metric horsepower (2,060 to 2,350 kW; 2,760 to 3,160 shp) for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged. She had two shafts and two 1.23 m (4 ft) propellers. The boat was capable of operating at depths of up to 230 metres (750 ft).
The submarine had a maximum surface speed of 17.7 knots (32.8 km/h; 20.4 mph) and a maximum submerged speed of 7.6 knots (14.1 km/h; 8.7 mph). When submerged, the boat could operate for 80 nautical miles (150 km; 92 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 8,500 nautical miles (15,700 km; 9,800 mi) at 10 knots (19 km/h; 12 mph). U-677 was fitted with five 53.3 cm (21 in) torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm (3.46 in) SK C/35 naval gun, (220 rounds), one 3.7 cm (1.5 in) Flak M42 and two twin 2 cm (0.79 in) C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
During a British air raid on Hamburg on 5 April 1945, U-677 was damaged while in the Howaldtswerke yard. In a second air raid four days later, U-677 as well as another U-boat, U-982, sank in the U-boat pen Fink II.