A good book to have is"Some Even Volunteered" by Alford S. Bradford
here is a very brief discription of one of the units.I know this is true, because I was part of the "First Wolfhounds" and took part in the missions Al Bradford tells about.
When in 1968 an American rifle battalion known as the "First Wolfhounds" landed near Dau Tieng, a rest area controlled by the North Vietnamese Army, they expected to interdict the NVA supply line there within three days. Instead, the soldiers found a prohibitive network of NVA troops, headquarters, hospitals, supplies, and local support for the NVA. It seemed impossible, even for the Wolfhounds, famed for their numbers and fighting strength. In the vivid prose of a mission survivor, Some Even Volunteered chronicles these brave soldiers' daily, deadly contact with the NVA, their attempts to win the villagers' trust, and how they struggled to accept and survive their circumstances. Eight months later, the Wolfhounds succeeded--destroying, in the process, an NVA unit of their own size.