The archives of the Bletchley Park Trust hold the largest known collection of intercepted German Air Force Enigma messages. They are rare survivors of millions of similar documents produced during the war, most of which were destroyed long ago. Dating from four days in November 1944, the documents show part of the process of deciphering messages. Each page has a distinctive front and back. The front shows the encrypted message in groups of five letters as it was originally transmitted by Morse code, and the back shows the decrypt of the same message printed on teleprinter tape glued to the page.
1 / 10 — Front of a ‘Red’ message, intercepted from the General Operational Key for the German Air Force (codenamed ‘Red’ at BP). Bletchley Park first began to regularly decipher ‘Red’ network messages from 22 May 1940 - their first break into German Enigma. Towards the bottom of the page is a Bombe machine menu, written in red pencil. This indicates how a Bombe machine could be set up to try to find the settings used on the Enigma machine that encrypted this message.