The receiver set his Enigma rotors to read HIT through the windows and then typed the next six letters in the message, KOSRLB. These were the indicators. The letters that lit up (LERLER) told him where to reset his rotors. Changing his rotor settings to read LER through the windows, the receiver now decrypted the rest of the message.

Because the clerk made up his own six-letter settings, the Polish cryptanalysts could occasionally guess the settings. The military did not allow an obvious setting such as ABC. However, cipher clerks sometimes chose settings like QWE (the first three letters on the keyboard) or names. In the example above, if the first three letters were HIT, the cryptanalysts could guess that KOS and RLB were the ciphers to LER, spelling out HITLER. BER was usually followed by the ciphers of LIN. One particular German code clerk continually used his girlfriend's name, Cillie, for his messages, and so these easy-to-guess indicators became known as 'Cillies.'(2)

The Poles could try these Cillie combinations relatively quickly. However, communication security policy discouraged this type of indicator, and most rotor settings were relatively random. To determine these random settings, the Poles relied on pure analysis and comparison. Henryk Zygalski developed a way to compare the message indicators. It involved stacks of perforated pages cut in exact positions. In our example, KOSRLB, the K and the R are ciphers for L. There are only certain combinations that allowed for that circumstance to occur. Holes in the perforated pages that lined up allowing K and R to correspond were considered as possible rotor settings. Cutting the pages took time, but once completed, they made the comparisons quickly. This system worked very well until the Germans changed their indicator system and sets of new pages had to be cut.

As the German military grew, so did the number of messages sent using the Enigma. It began to overwhelm the small staff of