U.S. Marines with 2nd Battalion, 1st Marine Regiment set up a defense as part of a Chemical Biological Radiological Nuclear Defense scenario during a combat readiness exercise aboard Camp Pendleton, Calif., June 18, 2015. U.S. Marines with 2/1 rehearse combat scenarios and improve infantry tactics in preparation for their future deployment with the 13th Marine Expeditionary Unit. (U.S. Marine Corps photo by Cpl. David Gonzalez, 13th Marine Expeditionary Combat Camera/Released)