U.S. Soldiers, assigned to 39th Signal Battalion, 2nd Signal Brigade, 5th Signal Command, perform push-ups while wearing their M40 Masks as they train on Chemical Biological Radiological Nuclear (CBRN) procedures for Commander's Prime Time Training, in the Training Support Center CBRN Chamber, on Chièvres Air Base, Chièvres, Belgium, March 18, 2015. (U.S. Army photo by Visual Information Specialist Pierre-Etienne Courtejoie/Released)