army unit vs vanguard

army unit and vanguard both are nouns.

Word	Noun	Adjective	Verb	Adverb
army unit	Yes	No	No	No
vanguard	Yes	No	No	No

As nouns, vanguard is a hyponym of army unit; that is, vanguard is a word with a more specific, narrower meaning than army unit:

army unit (noun)	vanguard (noun)
a military unit that is part of an army	the position of greatest importance or advancement; the leading position in any movement or field
	the leading units moving at the head of an army
	any creative group active in the innovation and application of new concepts and techniques in a given field (especially in the arts)