DoD photo by Staff Sgt. Andy M. Kin, US Air Force/ReleasedA U.S. Air Force base near Tucson, Arizona was locked down for about an hour on Monday following unconfirmed reports of "gunshot sounds" heard there, a base spokeswoman said. No further details of the incident at Davis-Monthan Air Force Base were immediately available, according to a spokeswoman for the base. The base announced the lockdown on social media shortly before 10 a.m.