time. An argument broke out between Vann and Ba. Finally, Vann radioed Ziegler at the command post at Tan Hiep and told him to ask the commander of the ARVN 7th Infantry Division to order Ba to move toward Ap Bac immediately. Shortly afterward, Ziegler returned with Dam's permission, and Ba was ordered to move his M113 carriers toward the white smoke rising from the burning hamlet. The American advisers were quietly confident that Ba's M113s could turn the tide of battle; on previous occasions, VC fighters often fled from the battlefield as soon as M113 armored personnel carriers turned up. However, in contrast to previous engagements, VC commander Hoang had ordered the soldiers of the 261st and 514th Battalions to throw everything they had at the South Vietnamese, as retreat through the muddy rice fields would result in certain death. The South Vietnamese M113s had no problem crossing the generally shallow streams and rivers typical of the Mekong Delta, but the heavy 10-ton M113s became bogged down in the deeper Cong Ba Ky Canal, forcing the crews and the infantry company on board to cut down brush and trees and fill the canal until it was shallow enough for the M113s to cross. The rescue operation was further delayed when Ba tried to obtain proper authorization to advance because he was under orders not to take commands directly from the American advisers. Vann, flying above the armored formation, demanded that Ba advance immediately. Ba replied that he would not take instructions from Americans. When Vann threatened to have Ba shot, he reluctantly continued to advance, although very slowly, toward the entrenched VC. Meanwhile, a fourth CH-21 returned to Ap Bac to rescue the downed helicopter crews. It was also heavily damaged by ground fire and forced to land on the muddy rice field. The VC had set a new record: the battle was the first time they had either destroyed or downed five helicopters within a few hours. At 13:30, Ba's M113 formation finally closed in on the downed helicopters on the west side of Ap Bac. The M113s approached the landing zone in a single file instead of in formation. They were immediately fired upon by VC inside the hamlet, who could concentrate their fire on one target at a time. The South Vietnamese M113 gun crews were exposed from the waist up, so they were easy targets