German submarine U-661

German submarine U-661 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 12 March 1941 by Howaldtswerke, Hamburg as yard number 810, launched on 11 December 1941 and commissioned on 12 February 1942 under Oberleutnant zur See Erich von Lilienfeld.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-661 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-661 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, and an anti-aircraft gun. The boat had a complement of between forty-four and sixty.

Service history
The boat's career began with training at 5th U-boat Flotilla on 12 February 1942, followed by active service on 1 October 1942 as part of the 3rd Flotilla for the remainder of her very short career. In one patrol she sank one merchant ship, for a total of.

Wolfpacks
U-661 took part in three wolfpacks, namely
 * Pfeil (12–22 September 1942)
 * Blitz (22–26 September 1942)
 * Wotan (12–15 October 1942)

Fate
U-661 was sunk on 15 October 1942 in the North Atlantic in position 53.7°N, -35.93333°W, by depth charges from Royal Navy destroyer HMS Viscount (D92). All hands were lost.