U.S. Marines with Headquarters and Service Battalion,

U.S. Marines with Headquarters and Service Battalion, and Weapons Field and Training Battalion, Marine Corps Recruit Depot Parris Island, line up along the wall as CS tear gas is released into the air during an individual protective equipment confidence exercise, also known as the gas chamber, aboard Marine Corps Recruit Depot Parris Island, S.C., Mar. 21, 2012. The required annual training helps Marines gain confidence in their ability to use the M50 joint service general-purpose gas mask.