Why did general westmoreland and secretary of defense Mcnamara want to americanize the war?

This question refers to the War in Vietnam. By 1965, the United States was reluctant about the idea of fully committing to the war in Vietnam. However, the involvement of the United States in the war continued to grow, as that same year, the number of American combatants grew from 50,000 to 100,000. This process of increased involvement was known as the "Americanization" of the war.

Those who disliked the idea of increased involvement generally did so because they believed that the payoff would be too small compared to the risk and cost of getting involved. However, Commanding General Westmoreland and Secretary of Defense McNamara disagreed.

They believed that the most important mission of the United States was to halt the spread of communism. Therefore, they thought that, under no circumstances should the Viet Cong be allowed to win. To this purpose, McNamara published his "Program of Expanded Military and Political Moves with Respect to Vietnam." This suggested that a victory of the Viet Cong would be impossible as long as the United States became fully involved in the war.