Vietnam was almost half jungle/forested which could make the rockets ineffective. Throw in the military's proud history of making units and equipment do things far outside their ability and training, like having MP's and maintenance units run convoy escort in soft sided Humvees, you have to ask yourself what you would do when you were ordered on a bombing run across the DMZ going 450 mph into a hornets nest of SAMs. They shot down F4 Phantoms like they were standing still and their top speed was almost 3X the Warthog. It would be great, maybe, to piss pound the Ho Chi Minh trail, but there is always gonna be that one dipshit admiral or general that would send them across the border on a bombing run.