The popularity of the red dot sight cannot be overstated. Red dots are the most popular AR-15 tactical optics for fast shooting at closer ranges, they’re one of the most commonly used optic solutions on the modern sporting rifle, and are becoming more and more popular on handguns as well.
Red dot technology and utility have come a long way since their ancestral origins in the 20th century. The Collimator sight was a precursor to the red dot. These types of sights allowed the shooter to keep both eyes open, superimposing a dot-shaped point of aim over the target when using binocular vision.
Collimator sights were used as far back as WWI, when artillery factions used them to launch their projectiles onto enemy positions.
A different type of sight, called an Occluded Eye Gunsight (OEG), which used Tritium or fiber optics to illuminate a dot in a closed-end black tube, was most famously used in the Son Tay raid in Vietnam. These OEGs were different from Collimator sights, in that they did not allow the shooter to observe the target beyond the illuminated aiming point by looking through the tube, rather a dot inside a black circle was superimposed over the target image when using binocular vision.
An American task force attached the Singlepoint OEG to their GAU-5A carbines’ carry handles with electrical tape as they attempted to free American POWs from a Vietnamese internment camp under cover of night.