German submarine U-634 was a Type VIIC U-boat built for Nazi Germany's Kriegsmarine for service during World War II. She was laid down on 23 September 1941 by Blohm & Voss, Hamburg as yard number 610, launched on 10 June 1942 and commissioned on 6 August 1942 under Oberleutnant zur See Hans-Günther Brosin.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-634 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 BBC GG UB 720/8 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-634 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 one twin C/30 anti-aircraft gun. The boat had a complement of between forty-four and sixty.
The boat's career began with training at 5th U-boat Flotilla on 6 August 1942, followed by active service on 1 February 1943 as part of the 9th Flotilla for the remainder of her service. In three patrols she sank one merchant ship, for a total of .
U-634 was sunk on 30 August 1943 in the North Atlantic in position , by depth charges from and , escorting the Allied convoys SL 135/MKS 22. All crew members of U-634 died.
U-634 took part in five wolfpacks, namely: