The Americans and the refugees they flew out were generally allowed to leave without intervention from either the North or South Vietnamese. Pilots of helicopters heading to Tan Son Nhat were aware that PAVN anti-aircraft guns were tracking them, but they refrained from firing. The Hanoi leadership, reckoning that completion of the evacuation would lessen the risk of American intervention, had instructed Dũng not to target the airlift itself. Meanwhile, members of the police in Saigon had been promised evacuation in exchange for protecting the American evacuation buses and control of the crowds in the city during the evacuation.