German submarine U-621

German submarine U-621 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 1 July 1941 by Blohm & Voss in Hamburg as yard number 597, launched on 19 March 1942 and commissioned on 7 May 1942 under Kapitänleutnant Horst Schünemann.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-621 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 Brown, Boveri & Cie GG UB 720/8 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-621 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 a 2 cm C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.

Service history
The boat's service began on 7 May 1942 for training as part of the 8th U-boat Flotilla. After training was completed she transferred to the 9th flotilla on 1 October 1942 for active service.

In ten patrols she sank four merchant ships for a total of, plus one auxiliary warship. She also damaged two more ships.

Wolfpacks
She took part in eleven wolfpacks, namely:
 * Panther (10 – 16 October 1942)
 * Puma (16 – 29 October 1942)
 * Raufbold (11 – 18 December 1942)
 * Hartherz (3 – 7 February 1943)
 * Ritter (11 – 26 February 1943)
 * Burggraf (4 – 5 March 1942)
 * Raubgraf (7 – 15 March 1943)
 * Amsel 1 (3 – 6 May 1943)
 * Elbe (7 – 10 May 1943)
 * Elbe 2 (10 – 14 May 1943)
 * Mosel (19 – 24 May 1943)

Fate
She was sunk by depth charges dropped by three Royal Canadian Navy destroyers, HMCS Ottawa (H31), HMCS Kootenay (H75) and HMCS Chaudiere (H99) on 18 August 1944 near La Rochelle at position 45.86667°N, -2.6°W.