Read my post again, I never said the FCC mandated the FBI or any government agency, I said the FBI started using encryption before the FCC mandated it.
Follow me here, DES was developed by the CIA and was classified at first and only the government eg. FBI used it on air. Later it was declassified and in use on the internet then in its infancy, the software was available but illegal to export, I had a copy BTW. Later still the ban on export was lifted and it became the most widely used encryption for on line banking, trade, etc.
This is not to be confused with the now ever popular encryption available for use with P-25 digital voice which came into use under the FCC mandate. DES3 is a three layer scheme, encrypted, encrypted again and encrypted a third time. While not impossible to break it takes so long (on the order of 10,000 years) it may be considered er... secure.
Of course interop is in the clear, how else could anyone communicate across divisions or agencies? There is no standard or common code for good reason, security.
Brookhaven is analog and so is Oyster Creek Nuclear, routine site operations chatter is SOOOooo boring I don't bother listening.