The 12th Marine Regiment (map designate: MAR 12 |||) was an infantry formation of the UNSC Marine Corps during the Human-Covenant war. This regiment was garrisoned in the Viery territory of the Human colony of Reach. It participated during the invasion to counter Covenant Army landing forces, primarily in the central theater.
At the time of the assault on Viery by the Covenant invasion forces, the 12th Marines had four battalions.
- 1st Battalion 12th Marines — (MAR || 1/12) Northern and Eastern Viery
- 3rd Battalion 12th Marines — (MAR || 3/12) Central Viery
- 4th Battalion 12th Marines — (MAR || 4/12) Central Viery
- 5th Battalion 12th Marines — (MAR || 5/12) Central Viery