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.
Mission
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
ICBMlaunch 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.
Chronology
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
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]
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
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.