German submarine U-431 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 4 January 1940 by Schichau-Werke in Danzig as yard number 1472, launched on 2 February 1941 and commissioned on 5 April 1941 under Kapitänleutnant Wilhelm Dommes (Knight's Cross).
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-431 had a displacement of when at the surface and while submerged. She had a total length of , a pressure hull length of , a beam of , a height of , and a draught of . The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of for use while surfaced, two AEG GU 460/8-276 double-acting electric motors producing a total of for use while submerged. She had two shafts and two 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-431 was fitted with five torpedo tubes (four fitted at the bow and one at the stern), fourteen torpedoes, one SK C/35 naval gun, 220 rounds, and a C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.
The boat's service began on 5 April 1941 for training as part of the 3rd U-boat Flotilla. Afterwards she transferred to the 29th flotilla operating in the Mediterranean on 1 January 1942. In 16 patrols she sank or damaged 11 ships in total.
She took part in one wolfpack, namely:
She was sunk on 21 October 1943 in the Mediterranean off Algiers at position by depth charges dropped from a RAF Wellington bomber of 179 Squadron, operating out of Gibraltar. All hands were lost.