I have a real union civil war infantry hat but I am wondering what kind of infantry hat it is?

My grandfather traded for it when he was a kid in the 30's or 40's.Its a blue union civil war hat, I think its either infantry or maybe even cavalry, the hat looks like a standard issue union hat its blue with a black visor and gold brass buttons on the sides there are no markings on the hat except for on the buttons and they say NG NJ on them.