hey Dennis , the first button is the U.S. Army Great Seal button that was first adopted and used in 1902 and is still being used today. the second button is your oldest , its a one piece and looks to be around the very early 1800's to about 1830 . this type usually will have either a makers mark or a quality mark on the back. the last is an anchor motif with the two hole stamped brass type probably much newer because of the lack of patina.
Dan