While KSCB was abandoned, the Marines continued to patrol the Khe Sanh plateau, including reoccupying the area with ARVN forces from 5–19 October 1968 with minimal opposition. On 31 December 1968, the 3rd Reconnaissance Battalion was landed west of Khe Sanh to commence Operation Dawson River West, on 2 January 1969 the 9th Marines and 2nd ARVN Regiment were also deployed on the plateau supported by the newly established Fire Support Bases Geiger and Smith; the 3-week operation found no significant PAVN forces or supplies in the Khe Sanh area. From 12 June to 6 July 1969, "Task Force Guadalcanal" comprising 1/9 Marines, 1st Battalion, 5th Infantry Regiment and 2nd and 3rd Battalions, 2nd ARVN Regiment occupied the Khe Sanh area in Operation Utah Mesa. The Marines occupied Hill 950 overlooking the Khe Sanh plateau from 1966 until September 1969 when control was handed to the Army who used the position as a SOG operations and support base until it was overrun by the PAVN in June 1971. The gradual withdrawal of US forces began during 1969 and the adoption of Vietnamization meant that, by 1969, "although limited tactical offensives abounded, US military participation in the war would soon be relegated to a defensive stance." According to military historian Ronald Spector, to reasonably record the fighting at Khe Sanh as an American victory is impossible. With the abandonment of the base, according to Thomas Ricks, "Khe Sanh became etched in the minds of many Americans as a symbol of the pointless sacrifice and muddled tactics that permeated a doomed U.S. war effort in Vietnam". Commencing in 1966, the US had attempted to establish a barrier system across the DMZ to prevent infiltration by North Vietnamese troops. Known as the McNamara Line, it was initially codenamed "Project Nine" before being renamed "Dye Marker" by MACV in September 1967. This occurred just as the PAVN began the first phase of their offensive, launching attacks against Marine-held positions across the DMZ. These attacks hindered the advancement of the McNamara Line, and as the fighting around Khe Sanh intensified, vital equipment including sensors and other hardware had to be diverted from elsewhere to meet the needs of the US garrison at Khe Sanh. Construction on the line was ultimately abandoned and resources were later diverted towards implementing a more mobile strategy. The precise nature of Hanoi's strategic goal at Khe Sanh is regarded as one of the most intriguing unanswered questions of the Vietnam War.