Long after the war s end, official World War II records listed the German submarine U-110 as sunk on 9 May 1941 by a British convoy a deliberate deception that hid the actual capture of a submarine that contained a working Enigma machine, codebooks, charts, and ciphers. As the official British historian of the naval war, Stephen Roskill did not reveal the secret in his authorized account. When this book was first published in 1959, the author set the record straight about the sinking but continued to hold back details of Ultra. Now, a new introduction puts the capture of U-110 into context and makes clear its vital importance to the code-breaking program of the Allies in World War II. Roskill s work is based on both documentary and eyewitness evidence and provides the most authoritative history of how the Enigma machine became a key instrument of the war effort.