German submarine U-857 was a Type IXC/40 U-boat of the Nazi German Kriegsmarine built for service during the Second World War. She was ordered on 5 June 1941, laid down on 16 November 1942, and launched on 25 May 1943. For her operational lifespan, she was commanded by Kapitänleutnant Rudolf Premauer and had a crew complement of 59. She undertook three patrols, the first was for training. She sank two ships for a total tonnage of 15,259 GRT, and damaged one other ship on her last two patrols. She sank the on 14 April 1945, the SS Swiftscout on 18 April 1945 and damaged the on 23 April 1945.