army base vs base of operations

army base and base of operations both are nouns.

Word	Noun	Adjective	Verb	Adverb
army base	Yes	No	No	No
base of operations	Yes	No	No	No

As nouns, base of operations is a hypernym of army base; that is, base of operations is a word with a broader meaning than army base:

army base: a large base of operations for an army
base of operations: installation from which a military force initiates operations

Other hypernyms of army base include base.

army base (noun)	base of operations (noun)
a large base of operations for an army	installation from which a military force initiates operations