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.: