The prank unfolded Friday night at Fort Bragg in North Carolina, which is home to US Army airborne and special operations forces.
"The incident resulted in an emergency response," the base said in a statement, adding that ordnance disposal teams cleared the area and a gate was closed.
"Costumes of this sort are not allowed on Fort Bragg," the base said.
Fort Bragg later removed the statement from its website, stating that comments posted on it had been "either profane, sophomoric, or did not treat the subject seriously."