U.S. Marines, of III Marine Expeditionary Force, participate in chemical, biological, radiological and nuclear (CBRN) training where Marines conduct a series of tests while wearing their protective gear in the gas chamber at Camp Courtney, Okinawa, Japan Dec. 22, 2011. During CBRN annual training, Marines are tested through various scenarios to mitigate hazards, wear the individual protective equipment and mask, and enter the gas chamber to ensure operational readiness.