I'll only briefly chime in on McNamara, seeing how you've gotten plenty of good comments already.
Being a tyke in front of the television during the Vietnam War and keeping my ears
open, about all I can tell you about McNamara is that he was an accomplished executive
(with Ford Motor Co.?) and a brilliant guy who, like a lot of America, got their
wires twisted by the Vietnam War...perhaps because it was an unconventional war,
fought out to a large degree in the press/media.
And that was a factor that the US leaders didn't have to worry about in WWII.
IIRC, he's also made some interesting comment about how close we (and our counterparts)
came to nuclear war during The Cold War. I think this was during some conference
that included Castro (maybe in Havana?).
Some other poster mentioned how the Communists used Cambodia as a strategic sanctuary
in the Vietnam War...IIRC, the movie "We Were Soldiers" shows how that was part
of the Vietnam War from the very start.
And Laos. Also, Thailand had an insurgency which threatened American forces there, as well.