What is 1st Civ Div?
In the military, specifically the US Marines, there are different divisions that Marines are assigned to - otherwise known as a unit on a large scale - such as the first division, etc.
The 1st civ div is a term for when a Marine is discharged and "joins the first civ div" as in becoming a "civ"ilian again.
Seargent Jones' contract ended. He just rejoined the 1st civ div.