There were reports of an active shooter situation at Walter Reed Medical Center in Bethesda, Maryland. But it turned out to be a drill.

WUSA is reporting that a Pentagon spokesperson said that it was an exercise on the campus.

Navy officials said it was an "ad hoc drill by tenant command."

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The base was given the all-clear by 3:20 p.m. EST.

Despite the assurance by military officials that it was a drill, a congressman who was on the base was sheltering in place and may not have known that. Maryland Congressman Dutch Ruppersberger was in a conference room with about 40 others taking shelter.

Shortly before the drill was confirmed by multiple media outlets, his representatives tweeted that he didn’t believe it was a drill.

Others posted video of the law enforcement response during the event.