The United States air campaign across rural South Vietnam, in conjunction with the actions of Allied ground forces toward the peasantry, spurred Vietcong recruitment during the period from early 1965 to late 1967.
At the beginning of 1965, the Communists had 103,000 men and women serving in their southern force structure. By March 1965, the same month the Marines landed at Danang, the number of Vietcong regulars and part-time guerrillas had increased to 137,000. The March estimate represented a thirty-three percent increase in total Vietcong strength in just a matter of months. Coincidently, that rapid and large increase in Vietcong strength occurred at the same time the U.S. intensified its air operations across rural South Vietnam.
In mid-1965, U.S. intelligence again revised upward its figures on enemy strength, estimating that the Vietcong possessed 153,000 regulars and guerrillas. Enemy troop levels jumped still higher later in the year (a period that coincided with a further intensification of U.S. air and ground combat operations across South Vietnam).
In the second half of 1965, U.S. intelligence concluded that the Vietcong recruited 9,000 new soldiers every month. By the end of 1965, the Vietcong fielded an army of 230,000 full-time troops and part-time guerrillas. The incredible rise in Vietcong military power in 1965 points to an irrefutable fact: U.S. air and ground operations during the first year of the U.S. military build-up in South Vietnam failed to weaken the Vietcong. Instead, the U.S.’s escalatory actions did the exact opposite, they boosted Vietcong recruitment.
In 1966 and 1967, the Vietcong continued to enhance their military power, even as U.S. troop levels in the South ballooned to nearly 500,000 men, and the number of U.S. bombing sorties in the South surpassed 10,000 per month.
At the end of 1966, the enemy force level in South Vietnam reached 288,000, an increase of nearly 60,000 from the previous year. That increase had been accomplished in spite of U.S. military operations that killed an estimated 100,000 enemy fighters. There was a slowdown in Vietcong recruitment in 1966, not because of a greater degree of popular support for the Saigon regime but because of the flight of upwards of 1.5 million rural refugees from Vietcong areas, which deprived the guerrillas of manpower.
In 1967, Vietcong recruitment again reached a monthly peak of 9,000 per month. A Department of Defense study noted that, “…the number of new South Vietnamese guerrillas the Vietcong were recruiting had gone up quite noticeably in 1967.” The Rand Corporation concluded that adult males from refugee families, and from homes where relatives had been killed or wounded by Allied military forces, contributed significantly to the expansion of Vietcong ranks.
By September 1967, the size of the Vietcong apparatus in the South reached truly impressive proportions. That month, the Central Intelligence Agency estimated total Communist strength (political and military) in the South at almost 500,000.
The dramatic rise in Vietcong strength between 1965 and late 1967 signaled Allied failure in the South Vietnamese countryside. Neither the U.S.’s military operations nor the GVN’s pacification program were taking hold in rural South Vietnam. Don Luce, whose nine years in South Vietnam gave him a deep understanding of rural life and culture, noted in the fall of 1967 that a palpable anti-Americanism and anti-GVN attitude pervaded the entire country, “I would say that there has been a very definite swing…from support and respect for Americans to one of resentment against what Americans are doing. I would say that there has been a very definite change and growing feelings against Americans in Vietnam.” Luce believed rural South Vietnam was less secure in late 1967 than it had been in 1965, especially along the coastal plain and in the Central Highlands where, “anti-Americanism has grown tenfold.”
Luce made a prediction that turned out to be remarkably prescient. Referring to the anger building across rural South Vietnam because of the destruction and dislocation wrought by American and ARVN military tactics, he said, “…if it continues…the resentment will continue to get more and more bitter…the pressures to hold this down will become stronger and stronger on the people, and…finally the whole thing will explode.” Three months later, the country did explode – with the Tet Offensive.
Back in July 1965, before the commitment of half a million U.S. troops to the war, the State Department’s George Ball sent President Johnson a memo warning him of the dangers of sending a large U.S. expeditionary force to South Vietnam. Ball wrote, “No one has demonstrated that a white ground force of whatever size can win a guerrilla war – which is at the same time a civil war between Asians – in jungle terrain in the midst of a population that refuses cooperation to the white forces (and the South Vietnamese)…Once we deploy substantial numbers of troops in combat it will become a war between the U.S. and a large part of the population of South Vietnam…Once large numbers of U.S. troops are committed to direct combat, they will begin to take heavy casualties in a war they are ill-equipped to fight in a non-cooperative if not downright hostile countryside.”
By the end of 1967, Ball’s prophecy had been borne out. A sizeable number of South Vietnam’s rural residents, as shown in the steady increases in the Vietcong’s total strength between early 1965 and late 1967, had risen up against the United States military presence. The war had become a struggle, as Ball had feared, “between the U.S. and a large part of the population of South Vietnam.” In early 1968, that hostile rural population, which included dispossessed refugees, assisted the Vietcong in attaining its greatest military success of the war.
 New York Times, “U.S. Death Toll for War is 1,350 for 1965,” January 2, 1966; The Senator Gravel Edition, The Pentagon Papers, The Defense Department History of United States Decisionmaking on Vietnam, Volume III, (Boston: Beacon Press, 1971), 406, 441; New York Times, “William Bundy Challenged on Vietcong Recruiting,” Neil Sheehan, October 17, 1967; New York Times, “Vietcong Defections Rise,” January 4, 1967; U.S. Congress, Senate, Committee on the Judiciary, Subcommittee to Investigate Problems Connected with Refugees and Escapees, “Hearings Before the Subcommittee to Investigate Problems Connected with Refugees and Escapees of the Committee on the Judiciary, United States Senate,” May 10, 18; August 16; September 21; October 9, 10, 11, 13, and 16, 1967, U.S. Senate, 90th Congress, 1st Session, (Washington, D.C.: GPO, 1968), 208.
 U.S. Congress, Senate, Committee on the Judiciary, Subcommittee to Investigate Problems Connected with Refugees and Escapees, “Hearings Before the Subcommittee to Investigate Problems Connected with Refugees and Escapees of the Committee on the Judiciary, United States Senate,” May 10, 18; August 16; September 21; October 9, 10, 11, 13, and 16, 1967, U.S. Senate, 90th Congress, 1st Session, (Washington, D.C.: GPO, 1968), 71.
 Ibid., 74.
 Ibid., 76.
 The Senator Gravel Edition, The Pentagon Papers, The Defense Department History of United States Decisionmaking on Vietnam, Volume IV, “Document 260, Memorandum for the President from George Ball, A Compromise Solution in South Vietnam, July 1, 1965,” (Boston: Beacon Press, 1971), 615-616.