U.S. Army Pfc. Quintin L. Beck, assigned to Charlie

U.S. Army Pfc. Quintin L. Beck, assigned to Charlie Company, 307th Expeditionary Signal Battalion, checks that his M40 field protective mask is functioning properly while conducting chemical, biological, radiological and nuclear sustainment training on Joint Base Elmendorf-Richardson, Alaska, July 16, 2015. The training culminated with masked Soldiers entering a sealed chamber filled with CS gas, also known as tear gas, then removing their protective gear to promote confidence in their equipment. (U.S. Air Force photo/Alejandro Pena)