61, the site of a mobile facility. All of these attacks were part of a coordinated effort to reduce the ability of the Americans to strike the communist logistical system during the Tet Offensive. In coordination with Tet, PAVN and the Pathet Lao launched a series of coordinated offensives in northern and southern Laos during 1968. The dry season offensive in northern Laos began with the communists again seizing the Nam Bac region of Military Region 1. This they adroitly managed, killing 200 Royal Army troops and capturing 2,400 more by 13 January. The offensive ground forward, slowly seizing more territory in the north. In the panhandle, the Laotian garrison at Ban Houi Sane, along Route 9 and west of the U.S. Marines' Khe Sanh Combat Base, was overrun by the PAVN 24th Regiment, 314th Division supported by Soviet-built PT-76 tanks. Further south, PAVN Group 565 advanced in Khammouane Province, seizing the rice harvest and placing themselves in position to overrun the cities of Saravane and Attopeu with little forewarning. The offensive then wound down and PAVN forces in southern Laos reorganized. On 12 January, one of the most unusual aerial battles of the Vietnam War took place. Two Soviet-built An-2 Colt biplanes of the North Vietnamese Vietnam People's Air Force attacked Lima Site 85 atop a craggy peak known as Phou Pha Thi. An Air America Bell 205 helicopter, which had taken off to avoid air-dropped 120mm mortar rounds, then began chasing one of the Colts which had already been struck by ground fire. The aircraft crashed while making evasive maneuvers. The Bell then went after the other Colt, and the helicopter's crew chief fired an AK-47 through a sliding window, shooting the biplane down. The PAVN were not through with Phou Pha Thi. The combined TACAN/TSQ-81 site was, by January, controlling 55 percent of Rolling Thunder strikes in northern North Vietnam and 20 percent of the strikes in the Barrel Roll area. On 11 March, Lima Site 85 was struck by an attack spearheaded by the sappers of the PAVN 41st Dac Cong Battalion and supported by the 923rd Infantry Battalion and the site was quickly overrun. Five of the USAF technicians manning the site managed to escape, but 11 more were missing in action. To replace Lima Site 85, Vang Pao moved against Moung Son and Na Khang, where a new site was erected in July. During