The Valentin submarine factory is a protective shelter on the Weser River at the Bremen suburb of Rekum [de; nds], built to construct German U-boats during World War II. The factory was under construction from 1943 to March 1945 using forced labour, but was damaged by air-raids and unfinished by the end of the war. The Valentin factory was the largest fortified U-boat facility in Germany, and was second only to those built at Brest in France.