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 to receive their gas masks during an individual protective equipment confidence exercise, also known as the gas chamber, aboard Marine Corps Recruit Depot Parris Island, S.C., March 21, 2012. The M50 joint service general-purpose gas mask is the United States armed forces gas mask, which began service in December 2009, replacing the M40 Field Protective Mask.