 The real struggle for the U.S. and ARVN forces in Cambodia was the effort at keeping their units supplied . Once again , the need for security before the operations and the <unk> with which units were transferred to the border regions precluded detailed planning and preparation . This situation was exacerbated by the poor road network in the border regions and the possibility of ambush for nighttime road convoys demanded that deliveries only take place during daylight . Aerial resupply , therefore , became the chief method of logistical <unk> for the forward units . Military engineers and aviators were kept in constant motion throughout the incursion zone . 
