USN vs Defense Department

USN and Defense Department both are nouns.

Word	Noun	Adjective	Verb	Adverb
USN	Yes	No	No	No
Defense Department	Yes	No	No	No

USN (noun)	Defense Department (noun)
the navy of the United States of America; the agency that maintains and trains and equips combat-ready naval forces	the federal department responsible for safeguarding national security of the United States; created in 1947