Wearing Nuclear, Biological & Chemical (NBC) protective gear, PV2 Ruben Gutierrez (second from left), PVT Patrick O'Neal and PFC Damien Wainright (third and fourth from left), all assigned to Headquarters and Headquarters Battery, 32nd Battalion, 31st Brigade, are briefed by SSGT Nathaniel Williams on their reaction to a simulated aerial chemical attack against their 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