Survivable Low Frequency Communications System

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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 high frequency 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.

SLFCS' primary advantage was it would suffer minimal 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.



GREEN PINE Stations[edit]

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]

Receive Only[edit]


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.


  • 1961
    • 29 Sep – Headquarters USAF issues Specific Operating Requirement 193, for the Survivable Low Frequency Communications System; system is envisioned to link Alternate Joint Command Center with command centers of SAC, NORAD, SAC numbered air forces with LF radio networks; a total of 18 transmit/receive (T/R) sites and 375 LF-receive only (R/O) in all SAC launch facilities, mobile Minuteman trains, SAC air base control rooms, and SAC UHF positive control stations in the northern tier
  • 1962
    • 12 Mar – Amendment to SOR 193 changes number of transmit T/R sites to 19 (three each at AJCC, SAC, NORAD, two each at 2d Air Force, 15th Air Force and 8th Air Force, one each at Larson AFB, Southern Alaska, Sondrestrom AB, and the United Kingdom; Full Operating Capability was extended from July 1964 to May 1965.
    • 27 Apr – A revised program directive delineated the network; T/R equipment would be installed at HQ SAC, the SAC numbered air force headquarters, and in the ABNCP, Alternate Joint Command Center (AJCC) and NORAD command center. 14 Green Pine stations, missile launch control centers, all SAC bomber wing command posts would have R/O terminals, as would the NORAD regional control centers. Initial Operating Capability (IOC) was placed at 1 Oct 1966.
  • 1968
    • 29 Jul 1968 – Silver Creek site accepted by SAC[4]
    • 19 Aug 1968 – Silver Creek site turned on for continuous operation[4]
    • 5 Sep 1968 – Silver Creek begins operational testing[4]
  • 1971
    • 16 Jun – SLFCS IOC obtained by SAC units
  • 1974
    • 26 Jul – HQ USAF approves Program 616A (Improved SLFCS); system would improve SLFCS by providing anti-jam protection, improved modems, increased range and make it compatible with the Navy LF/VLF system
  • 1978
    • SAC conducts Initial Operational Test and Evaluation (IOT&E) at Ellsworth AFB, South Dakota for Program 616A; test is successful
  • 1986
  • 1996
  • 2005
  • 2010 MMP – Minuteman Minimum Essential Emergency Communications Network Program now in the upgrade portion. Work In Progress. Advanced EHF will be available once upgrade is complete.

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