HQ vs command post

HQ and command post both are nouns.

Word	Noun	Adjective	Verb	Adverb
HQ	Yes	No	No	No
command post	Yes	No	No	No

As nouns, command post is a hyponym of HQ; that is, command post is a word with a more specific, narrower meaning than HQ:

HQ: the military installation from which a commander performs the functions of command
command post: military headquarters from which a military commander controls and organizes the forces

Other hyponyms of HQ include general headquarters, GHQ, guardhouse.

HQ (noun)	command post (noun)
the military installation from which a commander performs the functions of command	military headquarters from which a military commander controls and organizes the forces