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, who was 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.