Air Force Chief of Staff Gen. Mark A. Welsh III signs an agreement at the conclusion of the Conference of American Air Chiefs June 25, 2015, in Mexico City. The conference is an annual event sponsored by the System of Cooperation Among American Air Chiefs, which is headquartered at Davis-Monthan Air Force Base, Ariz., and includes representatives from 20 Western Hemisphere air forces. (U.S. Air Force photo/Capt. Bryan Bouchard)