This dissertation examines how Third Marine Amphibious Force (III MAF) headquarters fought the war in Vietnam's I Corps from 1965 to 1971. Previous studies have largely overlooked the role of the senior Marine command in Vietnam. A focus on the MAF's actions lends coherence to the historiography's patchy coverage of the conflict's most dangerous region. This research uses primary source records from eight archives to analyze each of III MAF's major command and staff functions: command and control, intelligence, operations, logistics, and plans. The project reveals four reasons for III MAF's inability to win the war in I Corps. First, a competent and determined enemy of North Vietnamese Army and Viet Cong regulars, guerrillas, and cadre conducted a complex form of hybrid warfare that the MAF never mastered. Second, Marine doctrine, organization, training, and experience undermined aspects of the headquarters' effectiveness as a corps-level command. Third, the MAF failed to accomplish its essential tasks of preventing the North Vietnamese Army from operating inside I Corps, destroying the insurgency's shadow government, and preparing ARVN's I Corps to protect the region independently. Finally, III MAF succeeded tactically but failed operationally - it won many battles but never crafted a campaign that accomplished its primary missions. By evaluating the headquarters' experience and assessing each of its warfighting functions, the text substantiates each claim and indicates how these factors contributed to III MAF's ultimate failure. This study concludes that III MAF was unprepared for the scope and scale of the conflict it encountered in I Corps, that it failed in its three most important tasks, and that the Marine Corps learned little from its longest and bloodiest experience of corps-level command. Among the many reasons for the MAF's difficulties, one factor loomed large: Marines placed little emphasis on corps-level command. In Vietnam, the MAF acted more as an administrative than a warfighting command. An institutional culture that stressed operations at the regimental level and below led inevitably to merely mediocre corps-level command. This story unpacks those conclusions and shows why the house the Marines helped construct did not stand.
