German submarine U-434 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
The U-boat was laid down on 20 January 1940 at the Schichau-Werke yard, Danzig, launched on 15 March 1941, and commissioned on 21 June 1941, Kapitänleutnant Wolfgang Heyda commanding.
U-434 sailed from Kristiansand, Norway on 2 November 1941, on her only war patrol. On 18 December, U-434 was sunk in the North Atlantic north of Madeira, Portugal, in position . The U-boat was forced to the surface by depth charges from the British escort destroyer and the destroyer . There were two dead and 42 survivors.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-434 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-434 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.
U-434 took part in two wolfpacks, namely: