My town library has a nice selection of books and is pretty as can be. In addition, New Hampshire interlibrary loan makes the Derry Public Library functionally gigantic.
I started research at DPL with Sebastian Junger's book, War. This is certainly what the local pediatrician should be seen carrying around! Lurid title aside this is a great piece of reporting in which Junger spends time with stressed troops operating out in the middle of nowhere. They fight insurgents who can pick the time and location of every battle and then disappear into the countryside. They struggle with ambushes, a hostile environment, an unfriendly alien local population, and what seems like an impossible mission objective. War was a very readable introduction to Vietnam, ironic because of course because the events and reporting took place in Afghanistan.
From Afghanistan I moved back a few decades to Michael Hess' Dispatches. This is Vietnam reporting that actually originated in Vietnam in the later 1960's. Junger writes crisp and factual accounts. In contrast Hess allows his experience and emotions to become part of his text. Dispatches in very readable and has a lot to say about the psychological price paid by the combatants. Hess has very clear biases (and so does Junger, just maybe not as overt) but they don't interfere with the value of the story being told. Why was Vietnam a different kind of war? Hess is a good person to turn to for an explanation.
Rounding out the round of public library work was Lt. General Hal Moore's We Were Soldiers Once, and Young. Then-Lt. Colonel Moore commanded an air cavalry unit in one of the first major American encounters of the war, the battle at Landing Zone X-Ray. The battle and subsequent encounters and ambushes were major learning experience for both the North Vietnamese and the Americans. It's not certain that the lessons learned were the Best ones, but the battle was highly influential on how the remainder of the war was conducted. Unlike Dispatches, We Were Soldiers... describes a pair of battles in great detail. The human component is absolutely present but the reader also gets a sense of how a battle might ebb and flow.
In hindsight the Derry Public Library really came through. I can't say these books were fun to read, but the history was valuable in general and certainly with regard to simulating the period in a game.