Internet/satellites/undersea-cables ... ALL very
vulnerable these days.
Old and slow as it is ... the Mil SHOULD actively
maintain the old-school comm links. This means
short-wave and/or LF ... preferably using old
TUBE tech which is much more EMP resistant.
NOT a gigantic investment here. This shit is
pretty CHEAP and EASY.
It also means comm-techs who are Morse-fluent
and some of those old One-Time-Pads you crack
open to decode/authenticate comms. Skip 'DEI',
always have The Best around.
"Modern" comm methods - TOO easy to destroy
or jam or corrupt. Gotta maintain the lower-
level methods too.
Old radio receivers ... cheap and easy.
Transmitters - one to 10000 watts - also easy.
Tube-tech ... few MAKE tubes these days but
it's old tech and not THAT hard. Some entities
still hand-make 'em. It it much more resistant
to EMP than any transistor-based stuff.
"Telegraph" over hard lines ... keep at least
a few of that option too. Really. The phone
companies STILL have LOTS of hard-lines. They
mostly don't USE them anymore - but the wires
are THERE. Last-ditch backups. KEEP some forever.
Fiber-Op lines CAN serve similar purposes.
And yea, it COULD get bad enough to NEED all that.
After some boring decades the conquerors are again
in motion.