US Navy vs bureau

US Navy and bureau both are nouns.

Word	Noun	Adjective	Verb	Adverb
US Navy	Yes	No	No	No
bureau	Yes	No	No	No

As nouns, bureau is a hypernym of US Navy; that is, bureau is a word with a broader meaning than US Navy:

US Navy: the navy of the United States of America; the agency that maintains and trains and equips combat-ready naval forces
bureau: an administrative unit of government

Other hypernyms of US Navy include agency, authority, federal agency, government agency, office.

US Navy (noun)	bureau (noun)
the navy of the United States of America; the agency that maintains and trains and equips combat-ready naval forces	furniture with drawers for keeping clothes
	an administrative unit of government