On 8 March 1965, 3,500 U.S. Marines were landed near Da Nang, South Vietnam. This marked the beginning of the American ground war. U.S. public opinion overwhelmingly supported the deployment. The Marines' initial assignment was the defense of Da Nang Air Base. The first deployment of 3,500 in March 1965 was increased to nearly 200,000 by December. The U.S. military had long been schooled in offensive warfare. Regardless of political policies, U.S. commanders were institutionally and psychologically unsuited to a defensive mission.

General William Westmoreland informed Admiral U. S. Grant Sharp Jr., commander of U.S. Pacific forces, that the situation was critical. He said, "I am convinced that U.S. troops with their energy, mobility, and firepower can successfully take the fight to the NLF (Viet Cong)". With this recommendation, Westmoreland was advocating an aggressive departure from America's defensive posture and the sidelining of the South Vietnamese. By ignoring ARVN units, the U.S. commitment became open-ended. Westmoreland outlined a three-point plan to win the war:

• Phase 1. Commitment of U.S. (and other free world) forces necessary to halt the losing trend by the end of 1965.
• Phase 2. U.S. and allied forces mount major offensive actions to seize the initiative to destroy guerrilla and organized enemy forces. This phase would end when the enemy had been worn down, thrown on the defensive, and driven back from major populated areas.
• Phase 3. If the enemy persisted, a period of twelve to eighteen months following Phase 2 would be required for the final destruction of enemy forces remaining in remote base areas.