Patrol craft are brown water. When we had corvettes it was just another name for a destroyer. I was referring to blue water vessels.
I would hardly include patrol craft (including ridged inflatables) in the same catagory as this destroyer.
It depends, as I said earlier, on whether you categorise warships on size (US Navy) or function (RN). If you are into size it goes Patrol craft-corvette-frigate-destroyer. The fact that the US navy no longer has any corvettes is because they dont see any need for such a small surface combatant. Foreign navies, particularly those that type on function, still do. There are plenty of 1000 ton plus ocean going patrol craft about. The French still use corvettes, allegedly to police their vast colonial empire (??)