German submarine U-421

German submarine U-421 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 20 January 1942 by Danziger Werft, Danzig as yard number 122, launched on 24 September 1942 and commissioned on 13 January 1943 under Leunant zur See Hans Kolbus.

Design
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-421 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-421 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 8th U-boat Flotilla on 13 January 1943, followed by active service on 1 November 1943 as part of the 9th Flotilla. On 1 April 1944, she transferred to 29th Flotilla for operations in the Mediterranean for the remainder of her service. In two patrols she sank no ships.

Wolfpacks
U-421 took part in six wolfpacks, namely
 * Coronel (4–8 December 1943)
 * Coronel 1 (8–14 December 1943)
 * Coronel 2 (14–17 December 1943)
 * Föhr (18–23 December 1943)
 * Rügen 6 (23–26 December 1943)
 * Hela (28 December 1943 – 1 January 1944)

Fate
U-421 was sunk on 29 April 1944 in the Mediterranean in position 43.11667°N, 5.91667°W at the military port of Toulon, France, in an air raid by US aircraft.