October 1954, the U.S. involvement in South Vietnam grew: a Military Assistance Advisory Group (later becoming the U.S. Military Assistance Command, Vietnam) to organize, train, and equip the armed forces of South Vietnam was established; helicopter companies to support the Vietnamese Army were deployed; combat and logistical airlift support was provided to South Vietnamese forces; Special Forces detachments were introduced, followed by the 5th Special Forces Group; U.S. tactical aircraft were deployed to South Vietnam and used in close air support; B-52 bombers were employed; and the deployment to South Vietnam of U.S. Army and Marine ground forces along with supporting air and naval forces was accelerated commencing in mid-1965. By the end of 1966 U.S. military forces in South Vietnam numbered 385,000 men.

Necessitating this increasing commitment of U.S. forces and resources to South Vietnam between 1954 and 1966 was the concomitant growth in the size and quality of Viet Cong and North Vietnamese forces in the south. The Communist Viet Minh had left many cadres in the south in 1954 which were grouped into a political-paramilitary organization under orders of Hanoi. This organization, known as the Viet Cong, was infused with large numbers of "regroupees" who had gone north between 1954-1955, received intensive political and military training, and returned to the south as cadres and leaders for the Viet Cong units and infrastructure. Pursuing initially a policy of subversion, espionage, and terror, this organization would turn to intensified guerrilla warfare, culminating in the employment of large military units. By 1960 some battalion-size units had been formed, and in later years Viet Cong military activity was conducted more and more by larger forces. By 1964 regular North Vietnamese Army units were starting to be deployed into South Vietnam to begin what Hanoi anticipated would be the final and decisive phase of the war. In that same year the enemy began to convert from weapons of various calibers and origins to a standard family of small arms. By the end of 1966 the total combat strength of the enemy was over 280,000 plus an additional 80,000 political cadre.

Tying together the various elements of the insurgency in South Vietnam was the Lao Dong (Worker's) Party regional committee for South Vietnam-the Central Office of South Vietnam (COSVN). All the various elements of the Communist organization in the south, military and civil, were and are responsive to directions from this office. Providing the administrative apparatus- the so-called Viet Cong shadow government- was the National Libera-