An initial report about a suspicious gunman at Davis-Monthan US Air Force Base in 2011 led to a series of communication breakdowns during a chaotic security incident.

The After Action Report released by the 355th Fighter Wing said that, in Air Force jargon, an unauthorised suspect carrying a gun on a military base is referred to as an “active shooter,” even if no weapon has been fired.

So, when a civilian at the Tucson facility mistakenly reported seeing a man with an assault rifle, military responders began talking about an “active shooter,” and civilian emergency dispatchers off the base spread word that a man with a gun had opened fire. Finally after nearly nine hours, Davis-Monthan officials declared the emergency over and announced there was no gunman. They declined to explain the false alarm.