US Navy vs Navy

US Navy and Navy both are nouns.

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

As nouns, US Navy and Navy are synonyms defined as:

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

Other synonyms of US Navy include United States Navy, USN.

US Navy (noun)	Navy (noun)
the navy of the United States of America; the agency that maintains and trains and equips combat-ready naval forces	the navy of the United States of America; the agency that maintains and trains and equips combat-ready naval forces