The problem in Vietnam was McNamara and the doctrine of proportional retaliation. So he quite literally flew planes in that were ordered to hang still just to get shot down, they weren’t allowed to respond, because, hey they were shooting at them with WW2 era flak cannons, a rocket wouldn’t be proportional. Dozens of planes were lost and they weren’t allowed to retaliate.
Same was the debacle over the AR15/M16 - it wouldn’t be fair to have burst fire, because the enemy didn’t have them, so soldiers were sent into the battlefield with semi-auto guns that were less capable than the same gun produced for civilians. Likewise it was decided that they should have slightly altered rounds to limit the production lines, because “gun control” was high on the Democrat agenda.
It literally took acts of Congress to force the JFK and LBJ administrations to properly equip the military. And then when LBJ signed the order to stop bombing the Vietnamese and retreat, they literally had thousands of people flee in shaggy boats and the US military refused to pick them up or assist them. Thousands drowned, about 90% of the boats did not reach their destination, between being fired upon by the communist regime and the poor situation these people were in.