The Battle of Lima Site 85, also called Battle of Phou Pha Thi, was fought as part of a military campaign waged during the Vietnam War and Laotian Civil War by the North Vietnamese People's Army of Vietnam (PAVN) and the Pathet Lao, against airmen of the United States Air Force (USAF)'s 1st Combat Evaluation Group, elements of the Royal Lao Army, Royal Thai Border Patrol Police, and the Central Intelligence Agency-led Hmong Clandestine Army. The battle was fought on Phou Pha Thi mountain in Houaphanh Province, Laos, on 10 March 1968, and derives its name from the mountaintop where it was fought or from the designation of a 700 feet (210 m) landing strip in the valley below, and was the largest single ground combat loss of United States Air Force members during the Vietnam War.