I think there were two huge systemic/structural problems with Vietnam (aside from whether or not we should have even been there). First, McNamara had the wrong mental model of what war is. He thought like a GM chairman, where you want to outproduce and out-deliver a competitor, ie, that it's a numbers game. That was never ever going to work. Second, and this is even more serious, top brass at DoD never called the civilians on the fact that they had their heads stuck up their asses. Instead, oddly enough, they acted like little division chiefs in a large organization: don't make waves, get face time with the boss, make sure the TPS cover sheets are attached, and so forth. This meant that not only were we wrong, we had no system in place to learn from it. There were several new ideas that look quite effective created in the lower ranks. They were all shot down before word got out too far, though. It didn't make the rest of the system look good.