Task: Question Answering
Input (English): Passage: 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, 5th Infantry Regiment (United States) 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.". 
Question: How many years did the Army occupy Hill 950? 
Answer type: Number 
Output (English): 2.