Republic of Korea Marines quickly put on gas masks June 3 at Doksukri Training Area, Republic of Korea, during Korean Military Exchange Program 15-9. U.S. and ROK Marines took nuclear, biological and chemical individual safety measures while practicing what water purification specialists do in midst of an attack. The ROK Marines are with Engineer Battalion, 1st ROK Marine Division. (U.S. Marine Corps photo by Cpl. Joey S. Holeman, Jr./ Released)