Gunnery Sgt. Zachary Burgart (left), project officer for amphibious reconnaissance equipment, and Master Sgt. Brad Colbert (right), project officer for small craft, MK25 closed-circuit underwater breathing apparatus in Spotsylvania, Virginia July 21, 2015. The system is a closed-circuit underwater breathing apparatus that allows its users to remain concealed in covert operations. - Gunnery Sgt. Zachary Burgart (left), project officer for amphibious reconnaissance equipment, and Master Sgt. Brad Colbert (right), project officer for small craft, MK25 closed-circuit underwater breathing apparatus in Spotsylvania, Virginia July 21, 2015. The system is a closed-circuit underwater breathing apparatus that allows its users to remain concealed in covert operations.