Cribs were fundamental to the British approach to breaking Enigma, but guessing the plaintext for a message was a highly skilled business. So in 1940 Stuart Milner-Barry set up a special Crib Room in Hut 8.[99][100]
Foremost amongst the knowledge needed for identifying cribs was the text of previous decrypts. Bletchley Park maintained detailed indexes[101] of message preambles, of every person, of every ship, of every unit, of every weapon, of every technical term and of repeated phrases such as forms of address and other German military jargon.[102] For each message the traffic analysis recorded the radio frequency, the date and time of intercept, and the preamble—which contained the network-identifying discriminant, the time of origin of the message, the callsign of the originating and receiving stations, and the indicator setting. This allowed cross referencing of a new message with a previous one.[103] Thus, as Derek Taunt, another Cambridge mathematician-cryptanalyst wrote, the truism that "nothing succeeds like success" is particularly apposite here.[90]
Stereotypical messages included Keine besonderen Ereignisse (literally, "no special occurrences"—perhaps better translated as "nothing to report"),[104] An die Gruppe ("to the group") [105] and a number that came from weather stations such as weub null seqs null null ("weather survey 0600"). This was actually rendered as WEUBYYNULLSEQSNULLNULL. The word WEUB being short for wetteruebersicht, YY was used as a separator and SEQS was common abbreviation of sechs ("six").[106] Field Marshal Erwin Rommel's Quartermaster started all of his messages to his commander with the same formal introduction.
