|Ordered:||2 April 1942|
|Class and type:||Type VIIC/41 submarine|
German submarine U-691 was a Type VIIC/41 U-boat of Nazi Germany's Kriegsmarine during World War II. Her construction by Howaldtswerke of Hamburg was ordered on 2 April 1942, suspended on 30 September 1943, and cancelled on 22 July 1944. The new Elektro Boat XXI design had made the Type VIIs obsolete.
Neal Stephenson's novel Cryptonomicon includes a fictitious U-691, a Type IXD/42, launched at Wilhelmshaven on 19 September 1940 (four years before IXD/42s were actually developed) and fitted with an experimental schnorkel.
- Helgason, Guðmundur. "U-691". German U-boats of WWII - uboat.net. Retrieved 17 February 2010.
- 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-691". German U-boats of WWII - uboat.net. Retrieved 29 December 2014.