German submarine U-337 was a Type VIIC U-boat of Nazi Germany's Kriegsmarine during World War II.
The submarine was laid down on 1 April 1941 at the Nordseewerke yard at Emden, launched on 26 March 1942, and commissioned on 6 May 1942 under the command of Oberleutnant zur See Kurt Ruwiedel.
German Type VIIC submarines were preceded by the shorter Type VIIB submarines. U-337 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-337 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-337 was mounted with two 2cm Flak C38 in a M 43U Zwilling mount with short folding shield on the upper Wintergarten. The M 43U mount was used on a number of U-boats (, , , , , , , , , , and ).
After training with the 5th U-boat Flotilla at Kiel, U-337 was transferred to the 6th U-boat Flotilla based at Saint-Nazaire in France for front-line service. After sailing from Kiel on 24 December 1942, the U-boat sailed north and then west into the Atlantic south of Iceland. Her last radio report, on 3 January 1943, gave her position as . The U-boat was never heard from again. Its fate remains an unsolved mystery.
A postwar assessment stated U-337 was sunk on 15 January 1943 southwest of Iceland by depth charges from a British Flying Fortress of No. 206 RAF. This attack was actually against U-632, inflicting no damage.