A fine place to start is the complete (thanks, US Army) collection of Vietnam Studies books, in electrical freebie form, at:
I especially like Ewell and Hunt’s “Sharpening the Combat Edge”, and it has a certain amount of statistical crunchiness.
There’s also an electrical freebie version of the classic “Seven Firefights in Vietnam”:
The abolute best thing in the world is I reckon John Kramer’s piece “Cohesion and Disintegration” in Strategy & Tactics no. 26, accompanying his splendid game “Grunt”; the article I think explains the Clausewitzian friction, or, if you prefer, embuggerance, of communicating across the mystifying variety of radio nets by which command is exercised in the modern era.
For background and atmosphere I’ll list my old favourites “Chickenhawk”, “Low Level Hell”, “Journal of a Plague Year”, “Once a Warrior King”, “Flower of the Dragon” and — as a backgrounder on the country rather than the war — “A Dragon Apparent”.
All the best,