Green Course A Marine Corps officer candidate participates in the combat course at the Officer Candidates School, Marine Corps Base Quantico, Va., June 18, 2018. Candidates must go through three months of intensive training. Marine Corps photo by Staff Sgt. Melissa Marnell SHARE: Download: Full Size (6.08 MB) Credit: Staff Sgt. Melissa Marnell VIRIN: 180618-M-DY697-0003C.JPG Photo Gallery