Ryan for her immersion in Operation Deadlight (post-war Allied operation) until 11 December 1945, when she was towed to sea by the British Navy tug HMS Freedom (W.139).U-991'' was sunk at 12.15am on 11 December 1945 in the North Atlantic, North-West off the coast of Ireland by a torpedo from the British submarine HMS Tantivy. Her wreck still lies at . References Bibliography German Type VIIC submarines U-boats commissioned in 1943 World War II submarines of Germany Ships built in Hamburg 1943 ships Maritime incidents in December 1945 Operation Deadlight Shipwrecks in the Atlantic Ocean