Since the cryptanalysts had no way of knowing which rotors the Germans had selected for use that day, each combination of rotors had to be checked. The order the rotors should be placed on the machine was known as a wheel order. Supervisors received blocks, or groups, of wheel orders and assigned one to each Bombe operator. The wheel order told the Bombe operators which rotors, I-VIII, to put on the machine and in which order they should be placed top to bottom. After a completed Bombe run, the wheel orders changed. But to keep things efficient, efforts were made to keep the number of rotor changes on a Bombe to a minimum. It took a Bombe operator only ten minutes to set the Bombe according to the menu. Once complete, a supervisor checked it, and then the operator turned the machine on. It ran for twenty minutes, looking for the electrical pathways that allowed each of the conditions listed on the menu to be true. Any pathways that fit the menu caused the Bombe to stop and print out the rotor settings, wheel order, and stecker connections at that point. When the Bombe completed its run, the Bombe operator handed the results to the supervisor and began setting the machine with the next wheel order. Twenty-four hours a day, every day, operators used the Bombes to search for Enigma settings, playing a major role in winning the Battle of the Atlantic and World War II.

Notes

1. Much of the information used in this appendix came from CDR Gilman McDonald, USNR (R), who was a senior watch officer of Bombe operations at Nebraska Avenue.

2. Conversation between former Wave Judy Parsons and the author,1999.

3. Ibid.