U.S. Air Force Master Sgt. Matt Leonard, an electro-environmental technician assigned to the 104th Maintenance Group, Barnes Air National Guard Base, Mass., inspects liquid oxygen tanks in a hardened aircraft shelter at Keflavik International Airport, Iceland, April 2, 2016. The tanks must be tested and fitted to the portable tank before transferring the liquid oxygen that will be used to replenish pilots’ oxygen supplies within the aircraft. (U.S. Air Force photo by Master Sgt. Kevin Nichols)