of the switches controlled solenoids which in turn enabled the movement of the rotors. The combination of cam rings and the controlling of a rotor by several switches created a most complex and irregular stepping. The exact wiring between switches and solenoids is still classified. The KL-7 was largely replaced by electronic systems such as the KW-26 ROMULUS and the KW-37 JASON in the 1970s, but KL-7s were kept in service as backups and for special uses. In 1967, when the U.S. Navy sailor John Anthony Walker walked into the embassy of the Soviet Union in Washington, DC seeking employment as a spy, he carried with him a copy of a key list for the KL-47. KL-7s were compromised at other times as well. A unit captured by North Vietnam is on display at NSA's National Cryptologic Museum. The KL-7 was withdrawn from service in June 1983, and Canada's last KL-7-encrypted message was sent on June 30, 1983, "after 27 years of service." The successor to the KL-7 was the KL-51, an off-line, paper tape encryption system that used digital electronics instead of rotors. See also NSA encryption systems Typex Enigma Notes Britannica (2005). Proc (2005) differs, saying that, "after the Walker family spy ring was exposed in the mid-1980s (1985)...immediately, all KL-7's were withdrawn from service" References Sources Jerry Proc's page on the KL-7, retrieved 2012-08-28. NSA Crypto Almanac 50th Anniversary - The development of the AFSAM-7, retrieved February 27, 2011. Technical details and history of the TSEC/KL-7, from Dirk Rijmenants' Cipher Machines & Cryptology, retrieved February 27, 2011. Patent for Rotor Re-entry by Albert W Small, filed 1944 from Free Patents On-line, retrieved February 27, 2011. "Cryptology", Encyclopædia Britannica. Retrieved 22 June 2005 from Encyclopædia Britannica Online. Card attached to KL-51 on display at the National Cryptologic Museum, 2005. External links TSEC/KL-7 with detailed information and many images on the Crypto Museum website Accurate TSEC/KL-7 Simulator (Windows), on Dirk Rijmenants' Cipher Machines & Cryptology Accurate TSEC/KL-7 Simulator (Java, platform-independent), released by MIT, on Crypto Museum website Rotor machines National Security Agency encryption devices Computer-related introductions in 1949 Products introduced in 1949