The North Vietnamese Army units deployed just north of the demilitarized zone in 1966 posed a serious and continuing threat to the security of Quang Tri and Thua Thien, the two northernmost provinces of South Vietnam. This is an account of the North Vietnamese attempts to seize control of these two provinces and of the response of the Free World Military Assistance Forces. The period covered by this narrative is from the spring of 1966 to the spring of 1968 and is the story, primarily, of U.S. Army units.