Officer Candidates School Marine Corps Staff Sgt. Keun Chung, a sergeant instructor at the Marine Corps Officer Candidates School, instructs officer candidates during an OCS preparation event at the Yakima Training Center in Yakima, Wash., April 8, 2016. Defense Secretary Ash Carter today announced proposed changes to the promotion rules for military officers in all services. Marine Corps photo by Sgt. Reece Lodder SHARE IMAGE: Download Image: Full Size (1.69 MB) Photo By: Sgt. Reece Lodder VIRIN: 160408-M-MM918-003.JPG Photo Gallery