British WW II Codebook Online

An A.C. pointed out Keith Lockstone's website which contains a complete scan of the Second World War codebook "British Cypher No. 5." An interesting look into history. "...when on 10 June [1943] the Admiralty at last replaced Naval Cipher No. 3 with No. 5, which proved quite secure, it was plain that the U-boats could never regain their former authority."