March 11, 2018 is the 50^th anniver­sary of one of the most noto­ri­ous episodes of the Secret War in Laos: the fall of the myth­i­cal Phu Pha Thi moun­tain, also known as Lima Site 85 or The Rock. Locat­ed in the Houaphanh province of north­east­ern Laos, Phu Pha Thi moun­tain reach­es heights of 1,786 meters, appear­ing as a giant mono­lith extend­ing from the heart of the Nam Et massif.

Ori­ent­ed on a north-south­east­ern axis and eight kilo­me­ters long, the moun­tain is a lime­stone fortress bor­dered by high cliffs to the north and east, dense forests with tigers and pan­thers to the west, and the Nam Et Nation­al Park to the south. In ancient times, Phu Pha Thi was a holy place for the eth­nic Khmus, Hmongs, and Dao peo­ples, who believed the moun­tain was inhab­it­ed by spir­its known as Phis. With its strange shape and reli­gious con­nec­tions, Phu Pha Thi resem­bles the infa­mous Cathar fortress of Montse­gur in south­west­ern France.

Dur­ing the Secret War in Laos, the Cen­tral Intel­li­gence Agency used Phu Pha Thi as a top-secret base, trans­form­ing it into an impreg­nable fortress over­look­ing the Sam Neua region, which was con­trolled by the Pathet Lao and the North Viet­namese Army (NVA). In August 1966, the US Air Force built a Tac­ti­cal Air Nav­i­ga­tion (TACAN) sta­tion on the moun­tain to sup­port the esca­lat­ing air war in the north­ern regions of Viet­nam and Laos. Because inter­na­tion­al agree­ments restrict­ed the US from open­ly con­duct­ing mil­i­tary oper­a­tions in Laos, the secret war was pri­mar­i­ly dri­ven by the CIA.

In 1967, a Com­bat Skyspot ground-direct­ed bomb­ing sys­tem (AN/T­SQ-81) was added. Dubbed Oper­a­tion Com­man­do Club, the sys­tem pro­vid­ed radar infor­ma­tion and assis­tance to USAF bomb­ing runs in north­ern Laos, North Viet­nam, and the Hanoi area, as well as to Oper­a­tions Rolling Thun­der and Bar­rel Roll (bomb­ing of the Ho chi Minh Trail).

Phu Pha Thi was defend­ed by 800 Hmongs from the Hmong Secret Army and by 300 Thai mer­ce­nar­ies. Nonethe­less, in Jan­u­ary 1968 the North Viet­namese – angered by the pres­ence of a US base in Com­mu­nist-con­trolled ter­ri­to­ry – launched an ini­tial aer­i­al attack on the moun­tain with two Antonov An‑2 air­crafts. When the aer­i­al attack failed, the NVA sent ground troops to sur­round the sacred moun­tain. The bat­tle for Phu Pha Thi raged until March 10, when a unit of North Viet­namese spe­cial forces and Red Hmongs man­aged to scale the cliffs. The US base fell on March 11, 1968 and was destroyed by aer­i­al sor­ties over a peri­od of two months.

On the Amer­i­can side, Lima Site 85 was clas­si­fied until 1983. The gov­ern­ment of Laos for­bade access to the high­ly sen­si­tive site until 2018, when it is sched­uled to be reopened. Secret Indochi­na pro­duc­tion depart­ment has stud­ied the area for more than two decades, orga­niz­ing a pre-sur­vey in 2013 and a sur­vey of the top and west­ern slope of the leg­endary moun­tain in 2018. The sum­mit and base are now acces­si­ble by 1,000 stairs from an ancient south­ern out­post, and there is poten­tial to orga­nize hik­ing on the west­ern and east­ern sides of the moun­tain along the Nam Et river.