German submarine U-523 was a Type IXC U-boat of the Nazi German Kriegsmarine during World War II. The submarine was laid down on 4 August 1941 at the Deutsche Werft yard in Hamburg as 'werk' 338. She was launched on 15 April 1942, and commissioned on 25 June under the command of Kapitänleutnant Werner Pietzsch. After training with the 4th U-boat Flotilla in the Baltic Sea, the U-boat was transferred to the 10th flotilla for front-line service on 1 February 1943.