“Since 13 September 1943, every message in that cipher has been read and since 1 April 1944 the average delay in ‘breaking’ the daily key has been about twelve hours. This means that for the last half of each day, we can read messages to and from Atlantic and Indian Ocean U-boats simultaneously with the enemy. In fact, during these hours the translation of every message sent by a U-boat is at hand about twenty minutes after it was originally transmitted. At present, approximately 15 percent of these keys are solved by the British and the remainder by OP-20-G.”
