Laos. By 24 December, six armed reconnaissance missions were being conducted per day, but the hoped for reaction from Hanoi did not materialize. The aircraft utilized to support the covert war were an odd assortment of vintage propeller-driven attack aircraft, high performance jet fighter-bombers, and World War II-era cargo airplanes. This hodgepodge of an air force with its peculiar mix of aircraft and aircrews flew for eight years in the crowded skies over Laos. The majority of the close air support missions flown in the northeast were conducted by Douglas A-1 Skyraiders and AT-28 Trojans. These propeller-driven Korean War-era aircraft came into their own in Southeast Asia, where their heavy ordnance loads, long loiter times, and high maneuverability at low altitudes made them more effective than the "fast movers" of the more modern jet Air Force. Before neutralization, one of the first American activities in support of the Hmong had been the establishment of Lima Sites, rough air strips across the country; during the early 1960s their number had grown to 200. The strategic Plain of Jars, was contested between the Hmong forces, PAVN, and the Pathet Lao, was a plateau north and northeast of Vientiane wide, covered with grass and small hills spread over an area of approximately . It quickly became evident that the cyclical pattern of the monsoon weather would dictate the timing and pace of military operations in the northeast. From November through May (the dry season), North Vietnamese and Pathet Lao forces advanced out of Sam Neua Province along Route 6 and out of the Barthelemy Pass through Ban Ban toward the Plain of Jars. The lack of roads and the primitive state of those that did exist forced the communists to stretch their lines of communication taut, inviting counterattack. This Vang Pao's forces did from June through October (the wet season), utilizing air power, air mobility, and guerrilla tactics to push the communists back to their starting places. Continuous U.S. air support for Barrel Roll operations was provided by the aircraft of the 602nd and 606th Special Operations Squadrons, elements of the 56th Air Commando Wing (as of 8 April 1967 the 56th Special Operations Wing), based at Nakhon Phanom Royal Thai Air Force Base, Thailand. On 25 October 1967, they were joined by the 22nd Special Operations Squadron. Pre-planned airstrikes in the Barrel Roll area were rare. Until 1968, most U.S. jet fighter-bomber