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An active shooter alert at the naval facility that is home to Walter Reed National Military Medical Center near Washington, D.C., turned out to be a drill that someone forgot to tell anyone about, the Navy said Tuesday.

The Navy said someone at Naval Support Activity Bethesda, in the Maryland suburbs of the capital, was planning a future drill when a tenant command "inadvertently" activated the facility's alert system at about 2 p.m. ET without including the words "exercise" or "drill."

Patients at Walter Reed, along with staff and visitors at the naval facility, scrambled for safety as security officers and Montgomery County police converged in response, NBC News says.

Law Enforcement said that it was common for institutions like NSA Bethesda to let them know in advance about exercises but that they were completely in the dark about Tuesday's accidental "drill."