and Henryk Zygalski, after many travails, perilous journeys and Spanish imprisonment, finally made it to Britain, where they were inducted into the Polish Army and put to work breaking German SS and SD hand ciphers at a Polish signals facility in Boxmoor. Due to their having been in occupied France, it was thought too risky to invite them to work at Bletchley Park. After the German occupation of Vichy France, several of those who had worked at PC Bruno were captured by the Germans. Despite the dire circumstances in which some of them were held, none betrayed the secret of Enigma's decryption. Operating shortcomings Apart from some less-than-ideal inherent characteristics of the Enigma, in practice the system's greatest weakness was the way that it was used. The basic principle of this sort of enciphering machine is that it should deliver a very long stream of transformations that are difficult for a cryptanalyst to predict. Some of the instructions to operators, however, and their sloppy habits, had the opposite effect. Without these operating shortcomings, Enigma would, almost certainly, not have been broken. The set of shortcomings that the Polish cryptanalysts exploited to such great effect included the following: The production of an early Enigma training manual containing an example of plaintext and its genuine ciphertext, together with the relevant message key. When Rejewski was given this in December 1932, it "made [his reconstruction of the Enigma machine] somewhat easier". Repetition of the message key as described in Rejewski's characteristics method, above. (This helped in Rejewski's solving Enigma's wiring in 1932, and was continued until May 1940.) Repeatedly using the same stereotypical expressions in messages, an early example of what Bletchley Park would later term cribs. Rejewski wrote that "... we relied on the fact that the greater number of messages began with the letters ANX—German for "to", followed by X as a spacer". The use of easily guessed keys such as AAA or BBB, or sequences that reflected the layout of the Enigma keyboard, such as "three [typing] keys that stand next to each other [o]r diagonally [from each other]..." At Bletchley Park such occurrences were called cillies. Cillies in the operation of the four-rotor Abwehr Enigma included four-letter names and German obscenities. Sometimes, with multi-part messages, the operator would not enter a key for a subsequent part of a message, merely leaving the rotors as they were at the end