Defoliation was judged in 1963 as improving visibility in jungles by 30–75% horizontally, and 40–80% vertically. Improvements in delivery systems by 1968 increased this to 50–70% horizontally, and 60–90% vertically. Ranch Hand pilots were the first to make an accurate 1:125,000 scale map of the Ho Chi Minh trail south of Tchepone, Laos by defoliating swaths perpendicular to the trail every half mile or so.