From Lee Russell- Tour of Duty military advisor 1987-1989:
Percell is the only member of the unit I can see as having enlisted in the Army. That would normally obligate him to three years service, rather than two. So he would still have more time to serve when he gets back from Vietnam. However, the Army also had an enlistment option of two years FOR COMBAT ARMS ONLY, and a choice of overseas assignments. I can see Percell telling the recruiter he wanted: Infantry-Vietnam.