I just read the amazing history of the Pilatus Porter, and how it was so effective in support of the PBYs or "Brown Water Navy" in Vietnam.
It was a stink because MacNamara killed the non competitive acquisition of the planes because one of his buddies intended to submit a plane for procurement and if the Porters were already in use and very effective his plane wouldn't sell.
We'll never know how many "river rats" lives could have been saved if they had been backed up on patrol by armed Porters.