[ASOC]

AN/FRC-117 - Survivable Low Frequency Communications System (SLFCS)

https://en.wikipedia.org/wiki/Survivable_Low_Frequency_Communications_System

Phase out started in 1974... all the ground stations long gone.

[Mariner]

SLFCS was an Air Force system, and had nothing to do with submarines.

However, the USN has a robust, redundant and survivable VLF broadcast system as an extension of the MEECN.