is, after each encipherment, the "fast" rotor would advance one step. Once every revolution of the fast rotor, the "medium" rotor would step once. Similarly, ever revolution of the medium rotor, the "slow" rotor would step, and so on for the other two rotors. However, which rotor was assigned as the "fast", "medium", "slow" etc. rotors was controlled by a set of five multi-switches. This gave a total of different rotor stepping patterns. The machine was equipped with a total of 10 rotors, each of which could be inserted "direct" or in reversed order, yielding possible rotor orderings and alignments. Introduction of the machine The design for this machine, which was designated the Converter M-228, or SIGCUM, was given to the Teletype Corporation, who were also producing SIGABA. Rowlett recommended that the adoption of the machine be postponed until after a study of its cryptographic security, but SIGCUM was urgently needed by the Army, and the machine was put into production. Rowlett then proposed that the machine used in the Pentagon code room be monitored by connecting a page-printing "spy machine". The output could be then studied to establish whether the machine was resistant to attack. Rowlett's suggestion was implemented at the same time the first M-228 machines were installed at the Pentagon in January 1943, used for the Washington-Algiers link. The machines worked as planned, and, initially, Rowlett's study of its security, joined by cryptanalyst Robert Ferner, uncovered no signs of cryptographic weakness. However, after a few days, a SIGCUM operator made a serious operating error, retransmitting the same message twice using the same machine settings, producing a depth. From this, Rowlett was able to deduce the underlying plaintext and keystream used by the machine. By 2 a.m., an analysis of the keystream allowed him to deduce the wiring of the fast and medium rotors, and of the output wiring. SIGCUM was immediately withdrawn from service, and work on a replacement system, SIGTOT — a one-time tape machine designed by Leo Rosen — was given top priority. Redesign Meanwhile, M-228 was redesigned to improve its security. Only five inputs, rather than thirteen, were energized. The five output contacts, instead of being used as the five output bits directly, were instead connected by three leads, each connected to different output point. That meant that an output bit could be energized by any of three different outputs from the rotor maze,