The Hammer’s Slammers series of Military SF stories and novels focus on a mercenary armored regiment in the 30th century. I based the fiction on my experience in 1970 with the 11th Armored Cavalry Regiment in Viet-Nam and Cambodia.
For information about the stories and novels, see Hammer’s Slammers Fiction
The series has been adapted to various forms of gaming. See Hammer’s Slammers Games