"We saw Vietnam as an element of the Cold War, and not what they saw it as – a civil war. We were wrong."
This lesson has huge relevance in our own time, though arguably political rather than logistical miscalculations are the biggest problem.
Did a lack of preparation in Iraq make the sectarian violence that helped to spawn Daesh inevitable? Or would global warming and drought have produced the chaos next door in Syria anyway?
Was the decision to support the uprising in Libya the wrong choice, or was it only made so by comparative underfunding of the reconstruction? These are complex questions, but the best answers must be sought if military operations in the Middle East are to be improved.
Proportionality should be a guideline in war
McNamara cautions that effective military operations are no good without moral guidelines to keep their destructiveness in check.
He admits that LeMay’s improvements in bombing operations crippled Japan, but feels guilty about the sheer scale of these missions, saying the total or near destruction of 67 Japanese cities by firebombs, and then two cities by nuclear bombs, was completely out of scale with the military objectives the US was trying to achieve.
While conflict in the present day is far less devastating than during World War Two, the principle is more relevant now than ever.
"Collateral damage" can mean large numbers of civilian casualties - as many Afghan civilians were killed during the NATO invasion of 2001 as American civilians died during the September 11th attacks.
With porous borders and homegrown terrorism, military campaigns risk becoming victims of their own success if they inspire deadly retribution.
'Belief' and 'seeing' are often both wrong
McNamara admits that the attack on US warship USS Turner Joy that precipitated the escalation of the country's involvement in Vietnam was, in fact, a complete mirage.
It was merely confusion, he says, in response to heightened tensions following an earlier naval confrontation between the US and North Vietnam two days before.
The parallel to phantom 'weapons of mass destruction' is obvious.
Be prepared to re-examine your reasoning
The Vietnam War was fought almost solely by the US against the North Vietnamese.
McNamara states that US military power should never be used unilaterally, and that if allies with similar values and interests cannot be convinced of the merits of a military operation, then America should be prepared to rethink.
Barack Obama showed restraint in the face of huge public pressure on his allies to not escalate matters in Syria.
Had similar pressure come from British and other foreign leaders in the run-up to the Iraq war, perhaps the Bush Administration (or, failing that, the US congress) might not have pressed forward with their plan to topple Saddam Hussein - and today’s Middle East might be less turbulent.