How many died from friendly fire during the Vietnam war?

Gunpowder did much to increase the effects of 'Blue on Blue' friendly fire in conflict. Before that the reason that Knights wore their coat of arms on their armour was to distinguish them to all, to prevent attack from their own side. The ability to kill at a distance has made friendly fire much much more common & has affected all combat situations ever since. Limited visibity in a tropical, jungle, situation makes identification of a target very very difficult and I'm sure this affected casualty rates in Vietnam. Whether this is more or less than other conflicts however I really couldn't speculate on.