not catch Bletchley Park by surprise, because captured material dated January 1941 had made reference to its development as an adaptation of the 3-rotor machine, with the fourth rotor wheel to be a reflector wheel. Indeed, because of operator errors, the wiring of the new fourth rotor had already been worked out. This major challenge could not be met by using existing methods and resources for a number of reasons. The work on the Shark cipher would have to be independent of the continuing work on messages in the Dolphin cipher. Solving Shark keys on 3-rotor bombes would have taken 50 to 100 times as long as an average Air Force or Army job. U-boat cribs at this time were extremely poor. It seemed, therefore, that effective, fast, 4-rotor bombes were the only way forward. This was an immense problem and it gave a great deal of trouble. Work on a high speed machine had been started by Wynn-Williams of the TRE late in 1941 and some nine months later Harold Keen of BTM started work independently. Early in 1942, Bletchley Park were a long way from possessing a high speed machine of any sort. Eventually, after a long period of being unable to decipher U-boat messages, a source of cribs was found. This was the Kurzsignale (short signals), a code which the German navy used to minimize the duration of transmissions, thereby reducing the risk of being located by high-frequency direction finding techniques. The messages were only 22 characters long and were used to report sightings of possible Allied targets. A copy of the code book had been captured from on 9 May 1941. A similar coding system was used for weather reports from U-boats, the Wetterkurzschlüssel, (Weather Short Code Book). A copy of this had been captured from on 29 or 30 October 1942. These short signals had been used for deciphering 3-rotor Enigma messages and it was discovered that the new rotor had a neutral position at which it, and its matching reflector, behaved just like a 3-rotor Enigma reflector. This allowed messages enciphered at this neutral position to be deciphered by a 3-rotor machine, and hence deciphered by a standard bombe. Deciphered Short Signals provided good material for bombe menus for Shark. Regular deciphering of U-boat traffic restarted in December 1942. Italian naval Enigma In 1940 Dilly Knox wanted to establish whether the Italian Navy were