German submarine U-423 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
She carried out one patrol. She did not sink or damage any ships.
She was sunk by a Norwegian aircraft northwest of the Faroe Islands on 17 June 1944.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-423 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-423 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 submarine was laid down on 16 March 1942 at the Danziger Werft (yard) at Danzig (now Gdansk), as yard number 124, launched on 7 November and commissioned on 3 March under the command of Oberleutnant zur See Joachim Methner.
She served with the 8th U-boat Flotilla from 3 March 1943 until her loss.
The boat's only patrol commenced with her departure from Kiel on 9 June 1944. On 17 June, she was sunk northeast of the Faroe Islands by depth charges dropped from a Norwegian PBY Catalina flying boat of No. 333 Squadron RAF.
Fifty-three men went down with the U-boat; there were no survivors.