German submarine U-677

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.

Attached to 5th U-boat Flotilla based at Kiel, U-677 completed her training period on 31 May 1944 and was assigned to front-line service.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-677 had a displacement of 769 t when at the surface and 871 t while submerged. She had a total length of 67.10 m, a pressure hull length of 50.50 m, a beam of 6.20 m, a height of 9.60 m, and a draught of 4.74 m. The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2800 to 3200 PS for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of 750 PS for use while submerged. She had two shafts and two 1.23 m propellers. The boat was capable of operating at depths of up to 230 m.

The submarine had a maximum surface speed of 17.7 kn and a maximum submerged speed of 7.6 kn. When submerged, the boat could operate for 80 nmi at 4 kn; when surfaced, she could travel 8500 nmi at 10 kn. U-677 was fitted with five 53.3 cm torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.8 cm SK C/35 naval gun, (220 rounds), one 3.7 cm Flak M42 and two twin 2 cm C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.

Service history
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, GS U-982, sank in the U-boat pen Fink II.