PVT Patrick O'Neal, Headquarters and Headquarters Battery, 32nd Battalion, 31st Brigade, wearing Nuclear, Biological & Chemical (NBC) protective gear, removes his mask once the "all clear" signal is given following a chemical attack against the camp. The chemical attacks are executed, using Russian helicopters, by members of Optec Threat Support Activity based at Biggs Army Airfield, Texas as part of the world's largest joint service, multi-national tactical air operations exercise