strategic Plain of Jars was under government control. This course of events led Ambassador Sullivan to declare: "We believe that damage to the enemy represents the best results per sortie by tactical air in Southeast Asia." By the end of the campaign in October, the operation had netted 25 tanks, 113 vehicles, six million rounds of ammunition, 6,400 weapons, and of fuel. That summer, sorties throughout the Barrel Roll area had risen from an average of 300 missions per month to an average 200 sorties per day. On the defensive (1970–1972) Beginning of the end The nature of the conflict in the northeast changed radically in mid-September 1969, when the communists were reinforced by the remaining two regiments of the 312th Division (the 165th and 209th), the refitted 316th Division, the 866th PAVN Infantry Regiment], the 16th PAVN Artillery Regiment, a tank company, six sapper and engineer battalions and ten Pathet Lao battalions. On 11 February 1970, these units launched Campaign 139, and by the 20th the Plain of Jars had been taken. Royal Lao forces withdrew to Muang Soui and five days later they abandoned Xieng Khouang. On 18 March Xam Thong fell and Vang Pao's stronghold at Long Tieng was threatened. As a stopgap, Washington approved Operation Goodlook, the first usage of Boeing B-52 Stratofortress bombers in northern Laos. During the first mission on 18 February 36 bombers delivered 1,078 tons of bombs. On 25 April the battered communist forces fell back, but the 316th PAVN Division and the 866th PAVN Infantry Regiment remained behind to assist the Pathet Lao. A CIA study concluded during the year that "About the most positive thing that can be said about Laos is that it still exists as a non-communist state." Souvannah Phouma was then 69 years old, visibly losing his vigour, and he had no apparent successor. The see-saw, seasonal conflict dragged on, but at the end of each cycle, the balance was somewhat more favorable to PAVN and the Pathet Lao. Due to the withdrawal of U.S. forces under the policy of Vietnamization, from 1 November 1968 until 23 February 1973, Barrel Roll competed for a share of diminishing U.S. tactical air assets. In December 1968, approximately 700 American strike aircraft had been available in-theater. By the spring of 1972, that number had fallen to 313. On 18 July, the Nakhon Phanom-based 22nd Special Operations Squadron was disbanded. Its