by connecting in line between the radio receiver and a teleprinter. It, in turn, was replaced by the more compact and reliable third generation KW-46. Strategic forces NSA has the responsibility to protect the command and control systems for nuclear forces. The KG-3X series is used in the U.S. government's Minimum Essential Emergency Communications Network and the Fixed Submarine Broadcast System used for transmission of emergency action messages for nuclear and national command and control of U.S. strategic forces. The Navy is replacing the KG-38 used in nuclear submarines with KOV-17 circuit modules incorporated in new long-wave receivers, based on commercial VME packaging. In 2004, the U.S. Air Force awarded contracts for the initial system development and demonstration (SDD) phase of a program to update these legacy generation systems used on aircraft. Trunk encryption Modern communication systems multiplex many signals into wideband data streams that are transmitted over optical fiber, coaxial cable, microwave relay, and communication satellites. These wide-band circuits require very fast encryption systems. The WALBURN family (KG-81, KG-94/194, KG-94A/194A, KG-95) of equipment consists of high-speed bulk encryption devices used primarily for microwave trunks, high-speed land-line circuits, video teleconferencing, and T-1 satellite channels. Another example is the KG-189, which support SONET optical standards up to 2.5 Gbit/s. Digital Data encryptors such as KG-84 family which includes the TSEC/KG-84, TSEC/KG-84A and TSEC/KG-82, TSEC/KG-84A and TSEC/KG-84C, also the KIV-7. Voice encryption True voice encryption (as opposed to less secure scrambler technology) was pioneered during World War II with the 50-ton SIGSALY, used to protect the very highest level communications. It did not become practical for widespread use until reasonable compact speech encoders became possible in the mid-1960s. The first tactical secure voice equipment was the NESTOR family, used with limited success during the Vietnam war. Other NSA voice systems include: STU I and STU II – These systems were expensive and cumbersome and were generally limited to the highest levels of command STU-III – These telephone sets operated over ordinary telephone lines and featured the use of security tokens and public key cryptography, making them much more user friendly. They were very popular as a result. Used since the 1980s, this device is rapidly being phased out, and will no longer be supported in the near future. 1910 Terminal – Made by a multiple of manufacturers, this device is mostly used as a secure modem. Like the STU-III, new technology has