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 Oberleutnant zur See Hans Kolbus.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-421 had a displacement of 769t when at the surface and 871t while submerged. She had a total length of 67.1m (220.1feet), a pressure hull length of 50.5m (165.7feet), a beam of 6.2m (20.3feet), a height of 9.6m (31.5feet), and a draught of 4.74m (15.55feet). The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of NaNPS for use while surfaced, two Siemens-Schuckert GU 343/38-8 double-acting electric motors producing a total of 750PS for use while submerged. She had two shafts and two 1.23abbr=onNaNabbr=on propellers. The boat was capable of operating at depths of up to .
The submarine had a maximum surface speed of and a maximum submerged speed of . When submerged, the boat could operate for at ; when surfaced, she could travel at . U-421 was fitted with five 53.30NaN0 torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one 8.82NaN2 SK C/35 naval gun, 220 rounds, and two twin 2sp=usNaNsp=us C/30 anti-aircraft guns. The boat had a complement of between forty-four and sixty.
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.
U-421 took part in six wolfpacks, namely:
U-421 was sunk on 29 April 1944 in the Mediterranean in position 43.1167°N 60°W at the military port of Toulon, France, in an air raid by US aircraft.