specially formed and vetted members of the 805th Signal Service Company of the US Army Signal Corps. The system was cumbersome, but it worked very effectively. When the Allies invaded Germany, an investigative team discovered that the Germans had recorded significant amounts of traffic from the system, but had erroneously concluded that it was a complex telegraphic encoding system. Significance SIGSALY has been credited with a number of "firsts"; this list is taken from (Bennett, 1983): The first realization of enciphered telephony The first quantized speech transmission The first transmission of speech by pulse-code modulation (PCM) The first use of companded PCM The first examples of multilevel frequency-shift keying (FSK) The first useful realization of speech bandwidth compression The first use of FSK-FDM (Frequency Shift Keying-Frequency Division Multiplex) as a viable transmission method over a fading medium The first use of a multilevel "eye pattern" to adjust the sampling intervals (a new, and important, instrumentation technique) See also Spread spectrum STU-III — a more recent voice encryption system. Speech coding References Notes William R. Bennett, Fellow, IEEE, "Secret Telephony as a Historical Example of Spread-Spectrum Communications," IEEE Transactions on Communications, Vol. COM-31, No. 1, January 1983, 99. Weadon, P., "Sigsaly Story", National Security Agency Central Security Service, January 2009 Further reading Top Secret Communications of WWII, by Donald Mehl, U.S. Army Signal Corps. The full story of SIGSALY and SIGTOT. Book available from the U.S. Army Signal Corps Association, a non profit organization. M. D. Fagen (editor), National Service in War and Peace (1925–1975), Volume II of A History of Engineering and Science in the Bell System (Bell Telephone Laboratories, 1978) pp. 296–317 External links "The SIGSALY story" "The start of the digital revolution" "1941 'Secret telephony' US patent 3967067 on the system." Ralph Miller is credited with a number of the related patents documented in Volume II of A History of Engineering and Science in the Bell System. Encryption devices Telecommunications in World War II Transatlantic telecommunications