A U.S. Air Force pilot's-eye view through an aircraft optical gunsight at dusk. The illuminated '100 MILS' reticle, with its ranging rings and diagonal stadiametric lines, was used to estimate distance to a target or another aircraft during Vietnam War-era close air support and night operations. Photographs like this one, taken directly through the gunsight glass, offer a rare glimpse of the tools pilots relied on for precision weapons delivery and formation flying after sundown. Project: 218964