In the early part of 1966, the U.S. Air Force was looking for ways to improve navigation in Southeast Asia (SEA), particularly over North Vietnam. This led to the installation of a number of TACAN stations in Laos that for political reasons had to be done under the guise of civilian support operations (read “non-military”). Both the U.S. and North Vietnam paid lip service to the fiction that Laos was a neutral country, and no foreign military were stationed there, when in reality we had a couple of hundred people spread over several sites, and the North Vietnamese had thousands on the Ho Chi Minh trail in eastern Laos. Through political maneuvering and with the support of the Central Intelligence Agency (CIA), a number of sites along the Laotian-North Vietnamese border were established.

Landing Site 85 (LS-85, also referred to in some sources as Lima Site 85) was one of the northern most TACAN sites established being north of the Plain of Jars and only about 125 nautical miles west-southwest of Hanoi. LS-85 was located on the top of Phou Pha Thi, a 5,800 foot karst mountain with near vertical cliff faces on three sides. The site was selected because of its near inaccessibility and because it had been used for years as a staging area for CIA supported Hmong guerilla fighters and American special operations and rescue helicopters. Most of the site’s supplies were delivered to a helipad on the top of the mountain, though some were hand-carried up a steep path from an STOL airstrip built by the CIA close to the Hmong encampment as the base. The existence and location of Site 85 was declassified in 1983.

The site was manned by USAF volunteers “sheep-dipped” as civilian Lockheed Aircraft employees Site protection was provided by the Hmong guerillas and Thai contract soldiers under the direction of CIA paramilitary officers. Air America, a CIA proprietary, provided logistic and aerial support for the facility, technicians and security forces.

In late 1966, the USAF decided to upgrade the site to provide bomb aiming capabilities in addition to the navigation facilities. This capability would be provided by a variant of the Radar Bombing Control System (MSQ-77). The MSQ-77 is a sophisticated piece of electronic equipment capable of directing air strikes without the pilot actually seeing his target. The advantages being that the aircraft can fly at an altitude reachable only by Surface-to-Air Missiles (SAM) and bombing can be accomplished in all types of weather day or night. The USAF ordered the creation of a mobile (wheel-less) variant designated TQS-81 that could be airlifted and placed at the site. This work was completed in early 1967 and began to provide precision, all-weather bombing capabilities to air operations in SEA. The highly classified site operated under the code name HEAVY GREEN.

It wasn’t long before the North Vietnamese figured out that our air forces had some sort of tactical advantage. Initial supposition, because of the accuracy being obtained, was some . . .