|Ordered:||20 January 1941|
|Builder:||Blohm & Voss, Hamburg|
|Laid down:||31 October 1941|
|Launched:||22 July 1942|
|Commissioned:||10 September 1942|
|Fate:||Torpedoed and sunk by the Soviet submarine S-101 in the Kara Sea on 28 August 1943|
|Class and type:||Type VIIC U-boat|
|Draught:||4.74 m (15.6 ft)|
|Test depth:||Calculated crush depth: 220 m (720 ft)|
|Complement:||4 officers, 40–56 enlisted|
German submarine U-639 was a Type VIIC U-Boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 31 October 1941 at Blohm & Voss in Hamburg as yard number 615, launched on 22 July 1942 and went into service on 10 September 1942. U-639 spent her entire career operating out of Norway. Over the course of four patrols she neither sank nor damaged any ships, and was sunk by the Soviet submarine S-101 in the Kara Sea while on a minelaying mission.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-639 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 BBC GG UB 720/8 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-639 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, and one twin 2 cm (0.79 in) C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.
- Blair, Clay (1998). Hitler's U-Boat War, The Hunted 1942–1945. New York: Random House. ISBN 978-0-679-45742-8.
- Busch, Rainer; Röll, Hans-Joachim (1999). German U-boat commanders of World War II : a biographical dictionary. Translated by Brooks, Geoffrey. London, Annapolis, Md: Greenhill Books, Naval Institute Press. ISBN 1-55750-186-6.
- Busch, Rainer; Röll, Hans-Joachim (1999). Deutsche U-Boot-Verluste von September 1939 bis Mai 1945 [German U-boat losses from September 1939 to May 1945]. Der U-Boot-Krieg (in German). IV. Hamburg, Berlin, Bonn: Mittler. ISBN 3-8132-0514-2.
- Gröner, Erich; Jung, Dieter; Maass, Martin (1991). U-boats and Mine Warfare Vessels. German Warships 1815–1945. 2. Translated by Thomas, Keith; Magowan, Rachel. London: Conway Maritime Press. ISBN 0-85177-593-4.
- Helgason, Guðmundur. "The Type VIIC boat U-639". German U-boats of WWII - uboat.net. Retrieved 30 December 2014.