The KY-28 Speech Security System worked just as it was supposed to do.  It provided a seamless interface for audio signals produced by the radio to be encrypted and decrypted for communications security.  But with that being said, it was a failed project. 
 Designed early in the Vietnam War for use in fighter aircraft, ships, ground installations, troops in the field, and vehicles, more than $110 million was spent to develop and field KY-28s, and over 2,200 were manufactured and installed.  It interfaced with the KY-38 man pack used by ground forces and KY-8 vehicular unit.  It used a physical key (the KYK-38 key) which was used to set the key code.  It then could communicate with any other unit keyed to the same code.  It had a self-protection feature that if it registered a large impact the key would reset so that if the aircraft crashed, no one could recover the key code.
The problem with the KY-28 was that the troops and pilots refused to use them because the lag between transmission and receipt of the message was considered a dangerous distraction during combat. The result was that US air-to-air and air-to-ground communications remained unencrypted and vulnerable to enemy exploitation throughout the war.
There only external difference to the F-4B when the KY-28 was installed is that Door 629 was added to the right forward fuselage. 

KY-28 Control Panel location
in Fwd F-4B cockpit
(click on picture to enlarge)
1 - KY-28 Control Panel in FWD Cockpit

1 - Door 629 for KY-28 Speech Security System
(click on picture to enlarge)

Revision History:
  •  17 MAR 2014 - Original Post
  • Artwork by Kim Simmelink
  • NAVAIR 01-245FDB-2-1.2
  • An Analysis of the Systemic Security Weaknesses of the U.S. Navy Fleet Broadcast System, by Laura Heath, MAJOR, USA

1 comment:

  1. In the F-4J the KY-28 was installed between the feet of the RIO. The planes came from the factory with a mounting bracket and one or two cables with multi-pin round plugs exposed. One of the first things we did on receipt of the planes was to design an aluminum cover that mated with the mounting brackets, had them chromated and painted, and installed them. This was done mostly to protect the cables until we were issued KY-28s to use (about 6 months later). We were deployed to the Med, so the operational difficulties were not as critical (nor the box as useful) as in 'Nam.
    It was possible for the pilot to configure the switches in such a way that radio communication was completely lost. The CO of VF-41 managed this one day. I think he didn't want to fly, but no one but he knows. It could have been fixed by the line AT, but he chose to down the plane.


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