The Marines, in conjunction with the Army of the Republic of Vietnam (ARVN), set about to wrest control of the populace in I Corps from the Viet Cong and help reassert the authority of the central government. The Allies launched an aggressive campaign designed to root out the enemy's source of strength--the local guerrilla. Allied battalion- and regimental-sized units screened this effort by seeking out and engaging Viet Cong main forces and North Vietnamese Army (NVA) elements. Smaller Marine and ARVN units went after the isolated guerrilla bands which preyed on the Vietnamese peasants. Thousands of fire team-, squad-, and platoon-sized actions took a heavy toll of the enemy and the Viet Cong were gradually pushed out of the populated areas. Whenever a village or hamlet was secured, civic action teams moved in to fill the vacuum and began the long, tedious process of erasing the effects of prolonged Communist domination. Progress was slow. Within a year, however, the area under Government security had grown to more than 1,600 square miles and encompassed nearly half a million people. As government influence extended deeper into the countryside, the security, health, economic well-being, and educational prospects of the peasants were constantly improved. There was an ever increasing number of enemy defectors and intelligence reports from, heretofore, unsympathetic villagers. By mid-1966, Allied military operations and pacification programs were slowly but seriously eroding the enemy's elaborate infrastructure and his hold over the people.(2) It soon became apparent to the leaders in the North that, unless they took some bold action, ten years of preparation and their master plan for conquest of South Vietnam would go down the drain. From the Communists' standpoint, the crucial matter was not the volume of casualties they sustained, but the survival of the guerrilla infrastructure in South Vietnam. In spite of their disregard for human life, the North Vietnamese did not wish to counter the American military steamroller in the populated coastal plain of I Corps. There, the relatively open terrain favored the overwhelming power of the Marines' supporting arms. The enemy troops would have extended supply lines, their movement could be more easily detected, and they would be further away from sanctuaries in Laos and North Vietnam. In addition, when the propaganda-conscious NVA suffered a defeat, it would be witnessed by the local populace and thus shatter the myth of Communist invincibility.