The Bletchley Park Codebreakers by Michael Smith Page B

considerable accomplishment, since the theoretical maximum was seventy-two – the highest recorded figure by the Wrens was fifty-seven (twenty-six minutes per run).
    A good crib for the bombes consisted of between twenty and thirty letters, but about fifteen would do at a pinch (for example, ‘
Geraetklarmeldung
’ - equipment ready). Cribs comprising as many as seventy-five letters were not uncommon, while occasionally they were 200 or more letters long. Considering that for all practical purposes cribs had to be letter perfect, it is amazing that so many long cribs were found. The following crib was part of a series called ‘Sultan’s
Meldung
’, which broke Red on no fewer than six separate days in April 1943:
    EINS X MELDUNG KLAM X LUDWIG KLAM YY … YY SULTAN X ROEM X EINS CAESAR X GEHEIM [One Report. (Ludwig) … Sultan Roman one Caesar [=Ic (the intelligence officer)]. Secret]
    It was easily recognizable, since it was transmitted daily on specific frequencies at three set times by the
Luftwaffe’s Fliegerkorps
X (codenamed ‘Sultan’).
    A frequent crib on Phoenix, which was used by
Panzerarmee
Afrika for its high-level operational communications between divisions and Corps, read:
    NAQT RUHIG YY KEINE BESONDEREN VORKOMMNISSE YY [Quiet night. Nothing special to report.]
    To Welchman’s regret, the general responsible for the unit sending it was captured, with the result that the crib died out.
    Hut 6 benefited greatly from the German reluctance to make the
Stecker
in
Heer
and
Luftwaffe
key-lists completely random.
Stecker
were not repeated on two successive days: if B and X were connected on Friday, that combination was not used on Saturday. The compilers of
Luftwaffe
key-lists also had a rule by which a letter was not connected to the next letter in the alphabet (B was not connected to C,C to D, and so on). Bletchley added a ‘Consecutive
Stecker
Knockout’ (CSKO) modification to the bombes to take account of this restriction, by eliminating stops which included consecutively steckered letters. A different rule prevented any rotor being used on consecutive days in the same position in the machine. Thus in the day before and after rotor order II, V, I was used, rotor II could not be used in the left-hand (slow) position, rotor V in the middle position or I in the fast (right-hand) position, reducing the rotor orders to be tested to thirty-two, instead of sixty. In addition, a rule under which no rotor order was used more than once a month was very helpful, especially towards the end of a month. And some ciphers started to use only half the available rotor orders, which became known as ‘Nigelian’ wheel orders (possibly being named after Nigel Forward, a member of Hut 6).
    Hut 6 also derived considerable help from the following basic mistakes by the German cipher operators:
    a) ‘Psillies’ – psychological cillies. In an indicator such as ROMXLV, XLV would probably be the enciphered message key ‘MEL’ (making ROMMEL when combined with the
Grundstellung
‘ROM’), while TOBKST might be derived from TOBRUK.
     
    b) ‘Nearnesses’, which occurred when a cipher clerk, after selecting the
Grundstellung
(say HTB), calculated what the rotor positions would be three letters later (HTE here, if no rotor turnover was involved), typed them, producing, for example, DXX as the enciphered message key. Since his rotors were then at HTE, he did not have to reset them, and could therefore start typing the message text straightaway. The message key was then very ‘near’ to the
Grundstellung
– three letters away, so that this particular type of nearness was sometimes known as a ‘003’.
     
    The ROMMEL type of psilli and nearnesses each gave a three-letter crib, linking the unenciphered and enciphered message key.
    In September 1940, Hut 6 had broken Brown, which was used by the
Luftwaffe’s
KGr 100, a pathfinder type unit, and by the Sixth Company of the
Luftwaffe’s
Signals Experimental Regiment. Until