A false alert about an "active shooter" at the US military's biggest hospital sent panicked patients and staff scrambling for shelter Tuesday.
Police and local authorities rushed to the Walter Reed National Military Medical Center near Washington around 2.00 pm (1900 GMT) after someone activated a trial alert but failed to make clear that it was only a drill.
"The active shooter event... was the result of the improper use of a mass notification system by a tenant command aboard the installation," the Navy said in a statement.
"While preparing for an upcoming drill, the notification system was inadvertently enacted without containing the words 'EXERCISE' or 'DRILL.'"
The hospital itself was placed on lockdown and people told to "shelter in place."
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