USA vs in

USA and in both are nouns.

Word	Noun	Adjective	Verb	Adverb
USA	Yes	No	No	No
in	Yes	Yes	No	Yes

USA (noun)	in (noun)
the army of the United States of America; the agency that organizes and trains soldiers for land warfare	a unit of length equal to one twelfth of a foot
North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776

USA (adverb)	in (adverb)
	to or toward the inside of