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Due to technical limitations, this article uses an unusual title. It should be called  TSEC/ prefix.

Most U.S. government-approved, in communications security (COMSEC) equipment has designations in the form TSEC/KG-99, in which TSEC/ (note slash) is purely an identification for a designation system, not an abbreviation. The designation system is under the control of the National Security Agency (NSA). It complements the AN- system used for general military electronics, which does reserve certain of the letters in the AN/ system are reserved for NSA use.

While the designation system codes are quite complex and still contain special cases, the basic structure is:

  • First letter: What is its function?
  • Second letter: What information or physical materials does it process?
  • Optional third letter: What kind of component is it?

The next numbers indicate a main model number within the series, followed by a bewildering and inconsistent set of version levels, alternate configurations, etc. Sometimes, what may seem an incremental improvement gets an entirely new model number, while a radical change may get a version change only. In other words, grasp the general principles of the system, but know that you will have to examine a specific system to understand its designation nuances.

  • TSEC/KG-13 is a cryptographic key generator (code name PONTUS)
  • TSEC/KY-57 was a cryptographic speech encryptor (code name VINSON)
  • TSEC/KW-7 was a cryptographic key encryptor for asynchronous character data (i.e., "Teletype") (code name ORESTES)

Designation system codes

Letter Function Type Assembly
A - - Advancing
B - - Base of cabinet
C COMSEC equipment - Combining
D - - Drawer or Panel
E - - Strip or Chassis
F - - Frame or Rack
G General purpose Key generation -
H Cryptographic ancillary - Keyboard
I - Data transmission Translator or Reader
J - - Speech Processing
K Cryptographic - -
L - Literal conversion Repeater
M Manufacturing - Memory or Storage
N Non-cryptographic Signal conversion -
O - Multipurpose Observation
P - Materials Production Power
Q - - -
R - - Receiver
S Special purpose Special purpose Synchronizing
T - Testing, checking, maintenance Transmitter
U - Television Printer
V - - Removable communications security component
W - Teletypewriter Logic Programmer or Programming
X - Facsimile Special purpose
Y - Speech (ciphony) -
Z - -