 | Bletchley Park TourC Block Huts 3 and 4 each kept an Index containing all the details gleaned from intercepted messages. This was used by the Watch and Advisers in understanding the content of translated messages. As more and more information was revealed from the intercepted messages, a central Index became necessary. This was first housed in Hut 7 (now demolished) and later moved to C Block. Every conceivable scrap of intelligence was painstakingly catalogued, cross-referenced and indexed in a vast punched card installation. At the peak of activity, two million punch cards per week were used! Enormous lengths were taken to protect Ultra and to ensure that the Germans didn't discover that Enigma and Lorenz were being broken. Only the top Allied commanders were ever told that Ultra came directly from intercepted Axis messages. In order to ensure secrecy, the SLUs (Security Liaison Units) were formed. An SLU was attached to each Allied commander. This unit received the output from Bletchley Park and placed it before the commander. The SLU was responsible for ensuring that the message was read and then destroyed, and would also advise on any resultant action by the commander which could reveal to the enemy that his messages had been read. No action could be taken which would jeopardise Ultra. |
