The AN/FRC-117 Survivable Low Frequency Communications System (SLFCS) was a communications system designed to be able to operate, albeit at low data transfer rates, during and after a nuclear attack.[1] The system used both very low frequency (VLF), and low frequency (LF) radio bands.
SLFCS was used for United States nuclear forces' command and control communications for Emergency Action Message dissemination and force direction. Single channel, receive only capability was provided at ICBM launch control centers. The single channel operated between 14 kHz and 60 kHz to receive commands from remotely located Combat Operations Center – Transmit/Receive (T/R) sites; this low frequency range is only slightly affected by nuclear blasts. For example, the Silver Creek site typically transmitted at 34.5 kHz. The transmitter could be tuned to any designated frequency in the above mentioned range. Receivers could receive down to 14.0 kHz.
SLFCS' primary advantage was that it would experience minimal radio signal degradation as a result of nuclear detonations. It would be an alternate means of communication during and after detonations, providing a survivable command and control communications network for the Strategic Air Command (SAC), the Joint Chiefs of Staff (JCS), and North American Aerospace Defense Command (NORAD). SLFCS would also relay signals from the Navy's LF/VLF systems.
The GREEN PINE communication system took messages broadcast over SLFCS and 'upconverted' them to UHF messages for bombers headed north. There were a handful of GREEN PINE stations in the northern portions of Alaska and Canada.[2][3]
The first program (487L) took six years from the time of the initial requirement to full operation. The second part (616A), which was basically a modification of an already operational system, took 10 years.
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United States Air Force system numbers
| |
|---|---|
| 100–199 |
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| 200–299 |
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| 300–399 |
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| 400–499 |
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| 500–599 |
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| 600–699 |
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| 700–799 |
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| 800–899 |
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| 900–999 |
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1 Unknown or not assigned | |
