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Speech encryption device - this page is a stub

TSEC/KY-38 was a half-duplex manpack voice encryption device, developed by the United States National Security Agency (NSA) around 1964. The device is part of the NESTOR family of speech encryption devices and was heavily used during the Vietnam War. It is compatible with the KY-8 vehicular unit and the KY-28 aircraft unit. The KY-38 was succeeded in 1975 by the KY-57 [3].


The image on the right features a US soldier operating a PRC-77 manpack radio during the Vietnam War, in October 1969. Below the radio set is the KY-38 voice encryption unit, which is about the same size as the radio itself. The total weight of the kit must have been enormous.
US soldier in Vietnam operating a PRC-77 radio with KY-38 voice encryptor. 16 October 1969 [2].

The KY-38 was introduced in 1964, together with the other members of the NESTOR family, the KY-8 and the KY-38. They were first used in the Vietnam War from 1965 onwards and were only available in small numbers. In total, approx. 30,000 NESTOR devices were produced, before they were replaced by VINSON family members like the KY-57 from 1975 onwards. The last NESTOR units were decomissioned in the early 1980s.

PRC-77 radio
The AN/PRC-77 radio was in fact a PRC-25 that had been given a solid state RF power amplifier, and was modified for the connection of digital voice encryption equipment, by adding a so-called X-MODE to the circuitry. When in X-Mode, the filters in the audio path of transmitter and receiver are bypassed in order to obtain the full bandwidth.

 More about the PRC-77

Compatible devices
  • Vehicular Unit
  • KY-28
    Aircraft Unit
  • KY-38
    Manpack Unit
  1. Brooke Clarke, AN/KY-38 Secure Voice System
    Retrieved November 2016.

  2. SP4 Timothy F. Fease, Image of soldier with AN/PRC-77 and TSEC/KY-38
    16 October 1969. 53 Sig Bn. 3791-30/AGA69. 1

  3. Wikipedia, NESTOR (encryption)
    Retrieved November 2016.
  1. Declassified by USAPA, 30 January 1970.

Further information
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Crypto Museum. Created: Saturday 01 October 2016. Last changed: Sunday, 11 March 2018 - 08:29 CET.
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