During the summer of 1964, a war of nerves was taking place between the United States, North and South Vietnam. United States ground forces were present in South Vietnam, officially in an advisory role to the Army of the Republic of Vietnam (ARVN) at the invitation of the South Vietnamese government. United States forces could not attack communist forces unless provoked by aggressive action of the communist Viet Cong, or in some cases, by North Vietnamese Army (NVA) ground units in the South.