adulterations of commercial codes like the ABC code and the ACME code. These were solved in a snap. The key for one circuit was found to be 3141592, the first seven digits of the mathematical constant pi. Elizebeth called this circuit “the pie circuit.” Sometimes the Germans sent the key at the start of the message and in groups of three or four letters instead of five, indicating that there was something special about these letters and giving away that they were a key. When an unfamiliar system was encountered, and
