What frequency were you hearing these call signs? I'm guessing you were hearing them on the GHFS shortwave frequencies. They are most likely tactical call signs that change daily, so a given aircraft or base station changes names every 24 hours or so.
Despite the name changes, they are most likely the E-4B NAOC and E-6 TACAMO aircraft flying their airborne command and control duties...
The E-4's and E-6's can often be heard on 311 MHz & 321 MHz as well as the HF nets. But it would be unusual for the call signs to never change. How long have you been hearing these calls?
What are the context of the comms? Are they EAM's. You will hear EAM's on 311.0.
311.0 also is a standard Command Post frequency. If the comms sound like standard command post stuff its probably the ground callsign of the command post.
Here's a list I found of many command post callsigns that had been logged on 311.0
i am aware of this.
i have been listening to mil air for many years. i hear these calls on 311.0 never heard anything on 321.0 i also hear them on 11.175.
they are EAMs and sometimes it is relayed. the voices change but not the callsigns. on uhf it is an aircraft.
i know the calls for the land stations in my area.