U-110 and HMS Bulldog

German submarine U-110 was a Type IXB U-boat of the German Kriegsmarine that operated during World War II. She was captured by the Royal Navy on 9 May 1941 and provided a number of secret cipher documents to the British. U-110's capture, later given the code name "Operation Primrose", was one of the biggest secrets of the war, remaining so for seven months. President Franklin D. Rooseveltwas only told of the capture by Winston Churchill in January 1942.

• http://en.wikipedia.org/wiki/German submarine U-110 (1940)