The second phase of the helilift began the next morning with the two unarmed U.S. Army UH-1Bs making several trips to Landing Zone ZULU to lift out the disassembled ARVN 105mm howitzers. The Marine and VNAF transport helicopters followed and continued to shuttle troops out of the landing zone for three hours without encountering enemy opposition. Then a departing flight of UH-34Ds drew fire from a nearby ridgeline. One of the escorting UH-1Bs immediately marked the suspected target for the VNAF T-28s and the attack aircraft bombed and strafed the position. The Communist activity ceased. After an overnight march, the covering force from Landing Zone HOTEL arrived at Landing Zone ZULU. Although they were not scheduled to be removed from the field until the next day, the schedule was adjusted and the 125 weary ARVN soldiers were flown to the secure assembly area on the afternoon of their arrival. This modification reduced the amount of work which would be required of the helicopters on the final day of the operation. The next phase of the helilift from ZULU on 17 August was characterized by increasing concern for security around the landing site. The general scheme for protecting the helicopters during this critical stage of the exercise was to establish two perimeters, one around the rim of high ground which surrounded the zone and another around the immediate landing site. The outer perimeter would be withdrawn first, leaving the inside ring of troops to deny the enemy direct access to the landing zone while the force from the outer perimeter boarded the helicopters. Once the Vietnamese soldiers were withdrawn from the rim of hills, the area within 300 meters of the close-in defenses would be automatically cleared for air strikes. Even with these precautions the helicopters would be extremely vulnerable to any enemy force that might rapidly occupy the high ground above Landing Zone ZULU following the withdrawal of the outer perimeter. Accordingly, once the troops from the outer defenses were staged for the helilift, the transport helicopters would be directed by the airborne ASOC to tighten the landing interval between aircraft from the usual five minutes to as short a time span as possible. By landing in such rapid succession, the dangerous final stage of the operation could be accomplished more quickly.