Between 1959 and 1975, the Democratic Republic of Vietnam (North Vietnam) used a series of trails running through Vietnam, Cambodia and Laos to transport weapons, supplies and reinforcements to the North Vietnamese Army and other sympathizers within South Vietnam. Originally a network of dirt roads, the Ho Chi Minh trail “continually expanded and improved until it had become a vast network which included, by 1974, all-weather surfaced roads, footpaths, and a network of gasoline pipelines,” according to the National Security Agency’s Center for Cryptologic History. The trail became a significant focal point for American military forces.

In 1965, the U.S. began a series of air raids to interdict the massive amounts of supplies rolling down the trail from North Vietnam. In order to determine the success or failure of their aerial effort, the U.S. used Air Force and Navy reconnaissance aircraft to routinely fly over the primary entry points into Vietnam from southern Laos at Tchepone and the Mu Gia and Ban Karai Passes.

The road networks running north and south were photographed at least once a week. The reconnaissance aircraft focused twice as often on the transit points into Vietnam and Cambodia from Laos. These flights sought to confirm the pilots’ visual estimate of the damage inflicted by U.S. night raids on North Vietnamese trucks running in near-dark conditions through Laos, down the trail to logistics staging areas and to truck parks serving as rest stops for continuing journeys. This reconnaissance effort sought to define both mission effectiveness and targets for the next day’s raids.